1 //===- InstructionCombining.cpp - Combine multiple instructions -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // InstructionCombining - Combine instructions to form fewer, simple
11 // instructions. This pass does not modify the CFG. This pass is where
12 // algebraic simplification happens.
14 // This pass combines things like:
20 // This is a simple worklist driven algorithm.
22 // This pass guarantees that the following canonicalizations are performed on
24 // 1. If a binary operator has a constant operand, it is moved to the RHS
25 // 2. Bitwise operators with constant operands are always grouped so that
26 // shifts are performed first, then or's, then and's, then xor's.
27 // 3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible
28 // 4. All cmp instructions on boolean values are replaced with logical ops
29 // 5. add X, X is represented as (X*2) => (X << 1)
30 // 6. Multiplies with a power-of-two constant argument are transformed into
34 //===----------------------------------------------------------------------===//
36 #define DEBUG_TYPE "instcombine"
37 #include "llvm/Transforms/Scalar.h"
38 #include "InstCombine.h"
39 #include "llvm-c/Initialization.h"
40 #include "llvm/ADT/SmallPtrSet.h"
41 #include "llvm/ADT/Statistic.h"
42 #include "llvm/ADT/StringSwitch.h"
43 #include "llvm/Analysis/ConstantFolding.h"
44 #include "llvm/Analysis/InstructionSimplify.h"
45 #include "llvm/Analysis/MemoryBuiltins.h"
46 #include "llvm/IR/DataLayout.h"
47 #include "llvm/IR/IntrinsicInst.h"
48 #include "llvm/Support/CFG.h"
49 #include "llvm/Support/CommandLine.h"
50 #include "llvm/Support/Debug.h"
51 #include "llvm/Support/GetElementPtrTypeIterator.h"
52 #include "llvm/Support/PatternMatch.h"
53 #include "llvm/Support/ValueHandle.h"
54 #include "llvm/Target/TargetLibraryInfo.h"
55 #include "llvm/Transforms/Utils/Local.h"
59 using namespace llvm::PatternMatch;
61 STATISTIC(NumCombined , "Number of insts combined");
62 STATISTIC(NumConstProp, "Number of constant folds");
63 STATISTIC(NumDeadInst , "Number of dead inst eliminated");
64 STATISTIC(NumSunkInst , "Number of instructions sunk");
65 STATISTIC(NumExpand, "Number of expansions");
66 STATISTIC(NumFactor , "Number of factorizations");
67 STATISTIC(NumReassoc , "Number of reassociations");
69 static cl::opt<bool> UnsafeFPShrink("enable-double-float-shrink", cl::Hidden,
71 cl::desc("Enable unsafe double to float "
72 "shrinking for math lib calls"));
74 // Initialization Routines
75 void llvm::initializeInstCombine(PassRegistry &Registry) {
76 initializeInstCombinerPass(Registry);
79 void LLVMInitializeInstCombine(LLVMPassRegistryRef R) {
80 initializeInstCombine(*unwrap(R));
83 char InstCombiner::ID = 0;
84 INITIALIZE_PASS_BEGIN(InstCombiner, "instcombine",
85 "Combine redundant instructions", false, false)
86 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
87 INITIALIZE_PASS_END(InstCombiner, "instcombine",
88 "Combine redundant instructions", false, false)
90 void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
92 AU.addRequired<TargetLibraryInfo>();
96 Value *InstCombiner::EmitGEPOffset(User *GEP) {
97 return llvm::EmitGEPOffset(Builder, *getDataLayout(), GEP);
100 /// ShouldChangeType - Return true if it is desirable to convert a computation
101 /// from 'From' to 'To'. We don't want to convert from a legal to an illegal
102 /// type for example, or from a smaller to a larger illegal type.
103 bool InstCombiner::ShouldChangeType(Type *From, Type *To) const {
104 assert(From->isIntegerTy() && To->isIntegerTy());
106 // If we don't have TD, we don't know if the source/dest are legal.
107 if (!TD) return false;
109 unsigned FromWidth = From->getPrimitiveSizeInBits();
110 unsigned ToWidth = To->getPrimitiveSizeInBits();
111 bool FromLegal = TD->isLegalInteger(FromWidth);
112 bool ToLegal = TD->isLegalInteger(ToWidth);
114 // If this is a legal integer from type, and the result would be an illegal
115 // type, don't do the transformation.
116 if (FromLegal && !ToLegal)
119 // Otherwise, if both are illegal, do not increase the size of the result. We
120 // do allow things like i160 -> i64, but not i64 -> i160.
121 if (!FromLegal && !ToLegal && ToWidth > FromWidth)
127 // Return true, if No Signed Wrap should be maintained for I.
128 // The No Signed Wrap flag can be kept if the operation "B (I.getOpcode) C",
129 // where both B and C should be ConstantInts, results in a constant that does
130 // not overflow. This function only handles the Add and Sub opcodes. For
131 // all other opcodes, the function conservatively returns false.
132 static bool MaintainNoSignedWrap(BinaryOperator &I, Value *B, Value *C) {
133 OverflowingBinaryOperator *OBO = dyn_cast<OverflowingBinaryOperator>(&I);
134 if (!OBO || !OBO->hasNoSignedWrap()) {
138 // We reason about Add and Sub Only.
139 Instruction::BinaryOps Opcode = I.getOpcode();
140 if (Opcode != Instruction::Add &&
141 Opcode != Instruction::Sub) {
145 ConstantInt *CB = dyn_cast<ConstantInt>(B);
146 ConstantInt *CC = dyn_cast<ConstantInt>(C);
152 const APInt &BVal = CB->getValue();
153 const APInt &CVal = CC->getValue();
154 bool Overflow = false;
156 if (Opcode == Instruction::Add) {
157 BVal.sadd_ov(CVal, Overflow);
159 BVal.ssub_ov(CVal, Overflow);
165 /// Conservatively clears subclassOptionalData after a reassociation or
166 /// commutation. We preserve fast-math flags when applicable as they can be
168 static void ClearSubclassDataAfterReassociation(BinaryOperator &I) {
169 FPMathOperator *FPMO = dyn_cast<FPMathOperator>(&I);
171 I.clearSubclassOptionalData();
175 FastMathFlags FMF = I.getFastMathFlags();
176 I.clearSubclassOptionalData();
177 I.setFastMathFlags(FMF);
180 /// SimplifyAssociativeOrCommutative - This performs a few simplifications for
181 /// operators which are associative or commutative:
183 // Commutative operators:
185 // 1. Order operands such that they are listed from right (least complex) to
186 // left (most complex). This puts constants before unary operators before
189 // Associative operators:
191 // 2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
192 // 3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
194 // Associative and commutative operators:
196 // 4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
197 // 5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
198 // 6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
199 // if C1 and C2 are constants.
201 bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
202 Instruction::BinaryOps Opcode = I.getOpcode();
203 bool Changed = false;
206 // Order operands such that they are listed from right (least complex) to
207 // left (most complex). This puts constants before unary operators before
209 if (I.isCommutative() && getComplexity(I.getOperand(0)) <
210 getComplexity(I.getOperand(1)))
211 Changed = !I.swapOperands();
213 BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
214 BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
216 if (I.isAssociative()) {
217 // Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
218 if (Op0 && Op0->getOpcode() == Opcode) {
219 Value *A = Op0->getOperand(0);
220 Value *B = Op0->getOperand(1);
221 Value *C = I.getOperand(1);
223 // Does "B op C" simplify?
224 if (Value *V = SimplifyBinOp(Opcode, B, C, TD)) {
225 // It simplifies to V. Form "A op V".
228 // Conservatively clear the optional flags, since they may not be
229 // preserved by the reassociation.
230 if (MaintainNoSignedWrap(I, B, C) &&
231 (!Op0 || (isa<BinaryOperator>(Op0) && Op0->hasNoSignedWrap()))) {
232 // Note: this is only valid because SimplifyBinOp doesn't look at
233 // the operands to Op0.
234 I.clearSubclassOptionalData();
235 I.setHasNoSignedWrap(true);
237 ClearSubclassDataAfterReassociation(I);
246 // Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
247 if (Op1 && Op1->getOpcode() == Opcode) {
248 Value *A = I.getOperand(0);
249 Value *B = Op1->getOperand(0);
250 Value *C = Op1->getOperand(1);
252 // Does "A op B" simplify?
253 if (Value *V = SimplifyBinOp(Opcode, A, B, TD)) {
254 // It simplifies to V. Form "V op C".
257 // Conservatively clear the optional flags, since they may not be
258 // preserved by the reassociation.
259 ClearSubclassDataAfterReassociation(I);
267 if (I.isAssociative() && I.isCommutative()) {
268 // Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
269 if (Op0 && Op0->getOpcode() == Opcode) {
270 Value *A = Op0->getOperand(0);
271 Value *B = Op0->getOperand(1);
272 Value *C = I.getOperand(1);
274 // Does "C op A" simplify?
275 if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
276 // It simplifies to V. Form "V op B".
279 // Conservatively clear the optional flags, since they may not be
280 // preserved by the reassociation.
281 ClearSubclassDataAfterReassociation(I);
288 // Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
289 if (Op1 && Op1->getOpcode() == Opcode) {
290 Value *A = I.getOperand(0);
291 Value *B = Op1->getOperand(0);
292 Value *C = Op1->getOperand(1);
294 // Does "C op A" simplify?
295 if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
296 // It simplifies to V. Form "B op V".
299 // Conservatively clear the optional flags, since they may not be
300 // preserved by the reassociation.
301 ClearSubclassDataAfterReassociation(I);
308 // Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
309 // if C1 and C2 are constants.
311 Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
312 isa<Constant>(Op0->getOperand(1)) &&
313 isa<Constant>(Op1->getOperand(1)) &&
314 Op0->hasOneUse() && Op1->hasOneUse()) {
315 Value *A = Op0->getOperand(0);
316 Constant *C1 = cast<Constant>(Op0->getOperand(1));
317 Value *B = Op1->getOperand(0);
318 Constant *C2 = cast<Constant>(Op1->getOperand(1));
320 Constant *Folded = ConstantExpr::get(Opcode, C1, C2);
321 BinaryOperator *New = BinaryOperator::Create(Opcode, A, B);
322 InsertNewInstWith(New, I);
324 I.setOperand(0, New);
325 I.setOperand(1, Folded);
326 // Conservatively clear the optional flags, since they may not be
327 // preserved by the reassociation.
328 ClearSubclassDataAfterReassociation(I);
335 // No further simplifications.
340 /// LeftDistributesOverRight - Whether "X LOp (Y ROp Z)" is always equal to
341 /// "(X LOp Y) ROp (X LOp Z)".
342 static bool LeftDistributesOverRight(Instruction::BinaryOps LOp,
343 Instruction::BinaryOps ROp) {
348 case Instruction::And:
349 // And distributes over Or and Xor.
353 case Instruction::Or:
354 case Instruction::Xor:
358 case Instruction::Mul:
359 // Multiplication distributes over addition and subtraction.
363 case Instruction::Add:
364 case Instruction::Sub:
368 case Instruction::Or:
369 // Or distributes over And.
373 case Instruction::And:
379 /// RightDistributesOverLeft - Whether "(X LOp Y) ROp Z" is always equal to
380 /// "(X ROp Z) LOp (Y ROp Z)".
381 static bool RightDistributesOverLeft(Instruction::BinaryOps LOp,
382 Instruction::BinaryOps ROp) {
383 if (Instruction::isCommutative(ROp))
384 return LeftDistributesOverRight(ROp, LOp);
385 // TODO: It would be nice to handle division, aka "(X + Y)/Z = X/Z + Y/Z",
386 // but this requires knowing that the addition does not overflow and other
391 /// SimplifyUsingDistributiveLaws - This tries to simplify binary operations
392 /// which some other binary operation distributes over either by factorizing
393 /// out common terms (eg "(A*B)+(A*C)" -> "A*(B+C)") or expanding out if this
394 /// results in simplifications (eg: "A & (B | C) -> (A&B) | (A&C)" if this is
395 /// a win). Returns the simplified value, or null if it didn't simplify.
396 Value *InstCombiner::SimplifyUsingDistributiveLaws(BinaryOperator &I) {
397 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
398 BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS);
399 BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS);
400 Instruction::BinaryOps TopLevelOpcode = I.getOpcode(); // op
403 if (Op0 && Op1 && Op0->getOpcode() == Op1->getOpcode()) {
404 // The instruction has the form "(A op' B) op (C op' D)". Try to factorize
406 Value *A = Op0->getOperand(0), *B = Op0->getOperand(1);
407 Value *C = Op1->getOperand(0), *D = Op1->getOperand(1);
408 Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op'
410 // Does "X op' Y" always equal "Y op' X"?
411 bool InnerCommutative = Instruction::isCommutative(InnerOpcode);
413 // Does "X op' (Y op Z)" always equal "(X op' Y) op (X op' Z)"?
414 if (LeftDistributesOverRight(InnerOpcode, TopLevelOpcode))
415 // Does the instruction have the form "(A op' B) op (A op' D)" or, in the
416 // commutative case, "(A op' B) op (C op' A)"?
417 if (A == C || (InnerCommutative && A == D)) {
420 // Consider forming "A op' (B op D)".
421 // If "B op D" simplifies then it can be formed with no cost.
422 Value *V = SimplifyBinOp(TopLevelOpcode, B, D, TD);
423 // If "B op D" doesn't simplify then only go on if both of the existing
424 // operations "A op' B" and "C op' D" will be zapped as no longer used.
425 if (!V && Op0->hasOneUse() && Op1->hasOneUse())
426 V = Builder->CreateBinOp(TopLevelOpcode, B, D, Op1->getName());
429 V = Builder->CreateBinOp(InnerOpcode, A, V);
435 // Does "(X op Y) op' Z" always equal "(X op' Z) op (Y op' Z)"?
436 if (RightDistributesOverLeft(TopLevelOpcode, InnerOpcode))
437 // Does the instruction have the form "(A op' B) op (C op' B)" or, in the
438 // commutative case, "(A op' B) op (B op' D)"?
439 if (B == D || (InnerCommutative && B == C)) {
442 // Consider forming "(A op C) op' B".
443 // If "A op C" simplifies then it can be formed with no cost.
444 Value *V = SimplifyBinOp(TopLevelOpcode, A, C, TD);
445 // If "A op C" doesn't simplify then only go on if both of the existing
446 // operations "A op' B" and "C op' D" will be zapped as no longer used.
447 if (!V && Op0->hasOneUse() && Op1->hasOneUse())
448 V = Builder->CreateBinOp(TopLevelOpcode, A, C, Op0->getName());
451 V = Builder->CreateBinOp(InnerOpcode, V, B);
459 if (Op0 && RightDistributesOverLeft(Op0->getOpcode(), TopLevelOpcode)) {
460 // The instruction has the form "(A op' B) op C". See if expanding it out
461 // to "(A op C) op' (B op C)" results in simplifications.
462 Value *A = Op0->getOperand(0), *B = Op0->getOperand(1), *C = RHS;
463 Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op'
465 // Do "A op C" and "B op C" both simplify?
466 if (Value *L = SimplifyBinOp(TopLevelOpcode, A, C, TD))
467 if (Value *R = SimplifyBinOp(TopLevelOpcode, B, C, TD)) {
468 // They do! Return "L op' R".
470 // If "L op' R" equals "A op' B" then "L op' R" is just the LHS.
471 if ((L == A && R == B) ||
472 (Instruction::isCommutative(InnerOpcode) && L == B && R == A))
474 // Otherwise return "L op' R" if it simplifies.
475 if (Value *V = SimplifyBinOp(InnerOpcode, L, R, TD))
477 // Otherwise, create a new instruction.
478 C = Builder->CreateBinOp(InnerOpcode, L, R);
484 if (Op1 && LeftDistributesOverRight(TopLevelOpcode, Op1->getOpcode())) {
485 // The instruction has the form "A op (B op' C)". See if expanding it out
486 // to "(A op B) op' (A op C)" results in simplifications.
487 Value *A = LHS, *B = Op1->getOperand(0), *C = Op1->getOperand(1);
488 Instruction::BinaryOps InnerOpcode = Op1->getOpcode(); // op'
490 // Do "A op B" and "A op C" both simplify?
491 if (Value *L = SimplifyBinOp(TopLevelOpcode, A, B, TD))
492 if (Value *R = SimplifyBinOp(TopLevelOpcode, A, C, TD)) {
493 // They do! Return "L op' R".
495 // If "L op' R" equals "B op' C" then "L op' R" is just the RHS.
496 if ((L == B && R == C) ||
497 (Instruction::isCommutative(InnerOpcode) && L == C && R == B))
499 // Otherwise return "L op' R" if it simplifies.
500 if (Value *V = SimplifyBinOp(InnerOpcode, L, R, TD))
502 // Otherwise, create a new instruction.
503 A = Builder->CreateBinOp(InnerOpcode, L, R);
512 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
513 // if the LHS is a constant zero (which is the 'negate' form).
515 Value *InstCombiner::dyn_castNegVal(Value *V) const {
516 if (BinaryOperator::isNeg(V))
517 return BinaryOperator::getNegArgument(V);
519 // Constants can be considered to be negated values if they can be folded.
520 if (ConstantInt *C = dyn_cast<ConstantInt>(V))
521 return ConstantExpr::getNeg(C);
523 if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
524 if (C->getType()->getElementType()->isIntegerTy())
525 return ConstantExpr::getNeg(C);
530 // dyn_castFNegVal - Given a 'fsub' instruction, return the RHS of the
531 // instruction if the LHS is a constant negative zero (which is the 'negate'
534 Value *InstCombiner::dyn_castFNegVal(Value *V, bool IgnoreZeroSign) const {
535 if (BinaryOperator::isFNeg(V, IgnoreZeroSign))
536 return BinaryOperator::getFNegArgument(V);
538 // Constants can be considered to be negated values if they can be folded.
539 if (ConstantFP *C = dyn_cast<ConstantFP>(V))
540 return ConstantExpr::getFNeg(C);
542 if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
543 if (C->getType()->getElementType()->isFloatingPointTy())
544 return ConstantExpr::getFNeg(C);
549 static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO,
551 if (CastInst *CI = dyn_cast<CastInst>(&I)) {
552 return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType());
555 // Figure out if the constant is the left or the right argument.
556 bool ConstIsRHS = isa<Constant>(I.getOperand(1));
557 Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
559 if (Constant *SOC = dyn_cast<Constant>(SO)) {
561 return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand);
562 return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC);
565 Value *Op0 = SO, *Op1 = ConstOperand;
569 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
570 return IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1,
571 SO->getName()+".op");
572 if (ICmpInst *CI = dyn_cast<ICmpInst>(&I))
573 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
574 SO->getName()+".cmp");
575 if (FCmpInst *CI = dyn_cast<FCmpInst>(&I))
576 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
577 SO->getName()+".cmp");
578 llvm_unreachable("Unknown binary instruction type!");
581 // FoldOpIntoSelect - Given an instruction with a select as one operand and a
582 // constant as the other operand, try to fold the binary operator into the
583 // select arguments. This also works for Cast instructions, which obviously do
584 // not have a second operand.
585 Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
586 // Don't modify shared select instructions
587 if (!SI->hasOneUse()) return 0;
588 Value *TV = SI->getOperand(1);
589 Value *FV = SI->getOperand(2);
591 if (isa<Constant>(TV) || isa<Constant>(FV)) {
592 // Bool selects with constant operands can be folded to logical ops.
593 if (SI->getType()->isIntegerTy(1)) return 0;
595 // If it's a bitcast involving vectors, make sure it has the same number of
596 // elements on both sides.
597 if (BitCastInst *BC = dyn_cast<BitCastInst>(&Op)) {
598 VectorType *DestTy = dyn_cast<VectorType>(BC->getDestTy());
599 VectorType *SrcTy = dyn_cast<VectorType>(BC->getSrcTy());
601 // Verify that either both or neither are vectors.
602 if ((SrcTy == NULL) != (DestTy == NULL)) return 0;
603 // If vectors, verify that they have the same number of elements.
604 if (SrcTy && SrcTy->getNumElements() != DestTy->getNumElements())
608 Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
609 Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
611 return SelectInst::Create(SI->getCondition(),
612 SelectTrueVal, SelectFalseVal);
618 /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
619 /// has a PHI node as operand #0, see if we can fold the instruction into the
620 /// PHI (which is only possible if all operands to the PHI are constants).
622 Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
623 PHINode *PN = cast<PHINode>(I.getOperand(0));
624 unsigned NumPHIValues = PN->getNumIncomingValues();
625 if (NumPHIValues == 0)
628 // We normally only transform phis with a single use. However, if a PHI has
629 // multiple uses and they are all the same operation, we can fold *all* of the
630 // uses into the PHI.
631 if (!PN->hasOneUse()) {
632 // Walk the use list for the instruction, comparing them to I.
633 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end();
635 Instruction *User = cast<Instruction>(*UI);
636 if (User != &I && !I.isIdenticalTo(User))
639 // Otherwise, we can replace *all* users with the new PHI we form.
642 // Check to see if all of the operands of the PHI are simple constants
643 // (constantint/constantfp/undef). If there is one non-constant value,
644 // remember the BB it is in. If there is more than one or if *it* is a PHI,
645 // bail out. We don't do arbitrary constant expressions here because moving
646 // their computation can be expensive without a cost model.
647 BasicBlock *NonConstBB = 0;
648 for (unsigned i = 0; i != NumPHIValues; ++i) {
649 Value *InVal = PN->getIncomingValue(i);
650 if (isa<Constant>(InVal) && !isa<ConstantExpr>(InVal))
653 if (isa<PHINode>(InVal)) return 0; // Itself a phi.
654 if (NonConstBB) return 0; // More than one non-const value.
656 NonConstBB = PN->getIncomingBlock(i);
658 // If the InVal is an invoke at the end of the pred block, then we can't
659 // insert a computation after it without breaking the edge.
660 if (InvokeInst *II = dyn_cast<InvokeInst>(InVal))
661 if (II->getParent() == NonConstBB)
664 // If the incoming non-constant value is in I's block, we will remove one
665 // instruction, but insert another equivalent one, leading to infinite
667 if (NonConstBB == I.getParent())
671 // If there is exactly one non-constant value, we can insert a copy of the
672 // operation in that block. However, if this is a critical edge, we would be
673 // inserting the computation one some other paths (e.g. inside a loop). Only
674 // do this if the pred block is unconditionally branching into the phi block.
675 if (NonConstBB != 0) {
676 BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
677 if (!BI || !BI->isUnconditional()) return 0;
680 // Okay, we can do the transformation: create the new PHI node.
681 PHINode *NewPN = PHINode::Create(I.getType(), PN->getNumIncomingValues());
682 InsertNewInstBefore(NewPN, *PN);
685 // If we are going to have to insert a new computation, do so right before the
686 // predecessors terminator.
688 Builder->SetInsertPoint(NonConstBB->getTerminator());
690 // Next, add all of the operands to the PHI.
691 if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
692 // We only currently try to fold the condition of a select when it is a phi,
693 // not the true/false values.
694 Value *TrueV = SI->getTrueValue();
695 Value *FalseV = SI->getFalseValue();
696 BasicBlock *PhiTransBB = PN->getParent();
697 for (unsigned i = 0; i != NumPHIValues; ++i) {
698 BasicBlock *ThisBB = PN->getIncomingBlock(i);
699 Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
700 Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
702 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
703 InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
705 InV = Builder->CreateSelect(PN->getIncomingValue(i),
706 TrueVInPred, FalseVInPred, "phitmp");
707 NewPN->addIncoming(InV, ThisBB);
709 } else if (CmpInst *CI = dyn_cast<CmpInst>(&I)) {
710 Constant *C = cast<Constant>(I.getOperand(1));
711 for (unsigned i = 0; i != NumPHIValues; ++i) {
713 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
714 InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
715 else if (isa<ICmpInst>(CI))
716 InV = Builder->CreateICmp(CI->getPredicate(), PN->getIncomingValue(i),
719 InV = Builder->CreateFCmp(CI->getPredicate(), PN->getIncomingValue(i),
721 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
723 } else if (I.getNumOperands() == 2) {
724 Constant *C = cast<Constant>(I.getOperand(1));
725 for (unsigned i = 0; i != NumPHIValues; ++i) {
727 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
728 InV = ConstantExpr::get(I.getOpcode(), InC, C);
730 InV = Builder->CreateBinOp(cast<BinaryOperator>(I).getOpcode(),
731 PN->getIncomingValue(i), C, "phitmp");
732 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
735 CastInst *CI = cast<CastInst>(&I);
736 Type *RetTy = CI->getType();
737 for (unsigned i = 0; i != NumPHIValues; ++i) {
739 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
740 InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
742 InV = Builder->CreateCast(CI->getOpcode(),
743 PN->getIncomingValue(i), I.getType(), "phitmp");
744 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
748 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end();
750 Instruction *User = cast<Instruction>(*UI++);
751 if (User == &I) continue;
752 ReplaceInstUsesWith(*User, NewPN);
753 EraseInstFromFunction(*User);
755 return ReplaceInstUsesWith(I, NewPN);
758 /// FindElementAtOffset - Given a type and a constant offset, determine whether
759 /// or not there is a sequence of GEP indices into the type that will land us at
760 /// the specified offset. If so, fill them into NewIndices and return the
761 /// resultant element type, otherwise return null.
762 Type *InstCombiner::FindElementAtOffset(Type *Ty, int64_t Offset,
763 SmallVectorImpl<Value*> &NewIndices) {
765 if (!Ty->isSized()) return 0;
767 // Start with the index over the outer type. Note that the type size
768 // might be zero (even if the offset isn't zero) if the indexed type
769 // is something like [0 x {int, int}]
770 Type *IntPtrTy = TD->getIntPtrType(Ty->getContext());
771 int64_t FirstIdx = 0;
772 if (int64_t TySize = TD->getTypeAllocSize(Ty)) {
773 FirstIdx = Offset/TySize;
774 Offset -= FirstIdx*TySize;
776 // Handle hosts where % returns negative instead of values [0..TySize).
782 assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
785 NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
787 // Index into the types. If we fail, set OrigBase to null.
789 // Indexing into tail padding between struct/array elements.
790 if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty))
793 if (StructType *STy = dyn_cast<StructType>(Ty)) {
794 const StructLayout *SL = TD->getStructLayout(STy);
795 assert(Offset < (int64_t)SL->getSizeInBytes() &&
796 "Offset must stay within the indexed type");
798 unsigned Elt = SL->getElementContainingOffset(Offset);
799 NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
802 Offset -= SL->getElementOffset(Elt);
803 Ty = STy->getElementType(Elt);
804 } else if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
805 uint64_t EltSize = TD->getTypeAllocSize(AT->getElementType());
806 assert(EltSize && "Cannot index into a zero-sized array");
807 NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
809 Ty = AT->getElementType();
811 // Otherwise, we can't index into the middle of this atomic type, bail.
819 static bool shouldMergeGEPs(GEPOperator &GEP, GEPOperator &Src) {
820 // If this GEP has only 0 indices, it is the same pointer as
821 // Src. If Src is not a trivial GEP too, don't combine
823 if (GEP.hasAllZeroIndices() && !Src.hasAllZeroIndices() &&
829 /// Descale - Return a value X such that Val = X * Scale, or null if none. If
830 /// the multiplication is known not to overflow then NoSignedWrap is set.
831 Value *InstCombiner::Descale(Value *Val, APInt Scale, bool &NoSignedWrap) {
832 assert(isa<IntegerType>(Val->getType()) && "Can only descale integers!");
833 assert(cast<IntegerType>(Val->getType())->getBitWidth() ==
834 Scale.getBitWidth() && "Scale not compatible with value!");
836 // If Val is zero or Scale is one then Val = Val * Scale.
837 if (match(Val, m_Zero()) || Scale == 1) {
842 // If Scale is zero then it does not divide Val.
843 if (Scale.isMinValue())
846 // Look through chains of multiplications, searching for a constant that is
847 // divisible by Scale. For example, descaling X*(Y*(Z*4)) by a factor of 4
848 // will find the constant factor 4 and produce X*(Y*Z). Descaling X*(Y*8) by
849 // a factor of 4 will produce X*(Y*2). The principle of operation is to bore
852 // Val = M1 * X || Analysis starts here and works down
853 // M1 = M2 * Y || Doesn't descend into terms with more
854 // M2 = Z * 4 \/ than one use
856 // Then to modify a term at the bottom:
859 // M1 = Z * Y || Replaced M2 with Z
861 // Then to work back up correcting nsw flags.
863 // Op - the term we are currently analyzing. Starts at Val then drills down.
864 // Replaced with its descaled value before exiting from the drill down loop.
867 // Parent - initially null, but after drilling down notes where Op came from.
868 // In the example above, Parent is (Val, 0) when Op is M1, because M1 is the
869 // 0'th operand of Val.
870 std::pair<Instruction*, unsigned> Parent;
872 // RequireNoSignedWrap - Set if the transform requires a descaling at deeper
873 // levels that doesn't overflow.
874 bool RequireNoSignedWrap = false;
876 // logScale - log base 2 of the scale. Negative if not a power of 2.
877 int32_t logScale = Scale.exactLogBase2();
879 for (;; Op = Parent.first->getOperand(Parent.second)) { // Drill down
881 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op)) {
882 // If Op is a constant divisible by Scale then descale to the quotient.
883 APInt Quotient(Scale), Remainder(Scale); // Init ensures right bitwidth.
884 APInt::sdivrem(CI->getValue(), Scale, Quotient, Remainder);
885 if (!Remainder.isMinValue())
886 // Not divisible by Scale.
888 // Replace with the quotient in the parent.
889 Op = ConstantInt::get(CI->getType(), Quotient);
894 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op)) {
896 if (BO->getOpcode() == Instruction::Mul) {
898 NoSignedWrap = BO->hasNoSignedWrap();
899 if (RequireNoSignedWrap && !NoSignedWrap)
902 // There are three cases for multiplication: multiplication by exactly
903 // the scale, multiplication by a constant different to the scale, and
904 // multiplication by something else.
905 Value *LHS = BO->getOperand(0);
906 Value *RHS = BO->getOperand(1);
908 if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
909 // Multiplication by a constant.
910 if (CI->getValue() == Scale) {
911 // Multiplication by exactly the scale, replace the multiplication
912 // by its left-hand side in the parent.
917 // Otherwise drill down into the constant.
918 if (!Op->hasOneUse())
921 Parent = std::make_pair(BO, 1);
925 // Multiplication by something else. Drill down into the left-hand side
926 // since that's where the reassociate pass puts the good stuff.
927 if (!Op->hasOneUse())
930 Parent = std::make_pair(BO, 0);
934 if (logScale > 0 && BO->getOpcode() == Instruction::Shl &&
935 isa<ConstantInt>(BO->getOperand(1))) {
936 // Multiplication by a power of 2.
937 NoSignedWrap = BO->hasNoSignedWrap();
938 if (RequireNoSignedWrap && !NoSignedWrap)
941 Value *LHS = BO->getOperand(0);
942 int32_t Amt = cast<ConstantInt>(BO->getOperand(1))->
943 getLimitedValue(Scale.getBitWidth());
946 if (Amt == logScale) {
947 // Multiplication by exactly the scale, replace the multiplication
948 // by its left-hand side in the parent.
952 if (Amt < logScale || !Op->hasOneUse())
955 // Multiplication by more than the scale. Reduce the multiplying amount
956 // by the scale in the parent.
957 Parent = std::make_pair(BO, 1);
958 Op = ConstantInt::get(BO->getType(), Amt - logScale);
963 if (!Op->hasOneUse())
966 if (CastInst *Cast = dyn_cast<CastInst>(Op)) {
967 if (Cast->getOpcode() == Instruction::SExt) {
968 // Op is sign-extended from a smaller type, descale in the smaller type.
969 unsigned SmallSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
970 APInt SmallScale = Scale.trunc(SmallSize);
971 // Suppose Op = sext X, and we descale X as Y * SmallScale. We want to
972 // descale Op as (sext Y) * Scale. In order to have
973 // sext (Y * SmallScale) = (sext Y) * Scale
974 // some conditions need to hold however: SmallScale must sign-extend to
975 // Scale and the multiplication Y * SmallScale should not overflow.
976 if (SmallScale.sext(Scale.getBitWidth()) != Scale)
977 // SmallScale does not sign-extend to Scale.
979 assert(SmallScale.exactLogBase2() == logScale);
980 // Require that Y * SmallScale must not overflow.
981 RequireNoSignedWrap = true;
983 // Drill down through the cast.
984 Parent = std::make_pair(Cast, 0);
989 if (Cast->getOpcode() == Instruction::Trunc) {
990 // Op is truncated from a larger type, descale in the larger type.
991 // Suppose Op = trunc X, and we descale X as Y * sext Scale. Then
992 // trunc (Y * sext Scale) = (trunc Y) * Scale
993 // always holds. However (trunc Y) * Scale may overflow even if
994 // trunc (Y * sext Scale) does not, so nsw flags need to be cleared
995 // from this point up in the expression (see later).
996 if (RequireNoSignedWrap)
999 // Drill down through the cast.
1000 unsigned LargeSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
1001 Parent = std::make_pair(Cast, 0);
1002 Scale = Scale.sext(LargeSize);
1003 if (logScale + 1 == (int32_t)Cast->getType()->getPrimitiveSizeInBits())
1005 assert(Scale.exactLogBase2() == logScale);
1010 // Unsupported expression, bail out.
1014 // We know that we can successfully descale, so from here on we can safely
1015 // modify the IR. Op holds the descaled version of the deepest term in the
1016 // expression. NoSignedWrap is 'true' if multiplying Op by Scale is known
1020 // The expression only had one term.
1023 // Rewrite the parent using the descaled version of its operand.
1024 assert(Parent.first->hasOneUse() && "Drilled down when more than one use!");
1025 assert(Op != Parent.first->getOperand(Parent.second) &&
1026 "Descaling was a no-op?");
1027 Parent.first->setOperand(Parent.second, Op);
1028 Worklist.Add(Parent.first);
1030 // Now work back up the expression correcting nsw flags. The logic is based
1031 // on the following observation: if X * Y is known not to overflow as a signed
1032 // multiplication, and Y is replaced by a value Z with smaller absolute value,
1033 // then X * Z will not overflow as a signed multiplication either. As we work
1034 // our way up, having NoSignedWrap 'true' means that the descaled value at the
1035 // current level has strictly smaller absolute value than the original.
1036 Instruction *Ancestor = Parent.first;
1038 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Ancestor)) {
1039 // If the multiplication wasn't nsw then we can't say anything about the
1040 // value of the descaled multiplication, and we have to clear nsw flags
1041 // from this point on up.
1042 bool OpNoSignedWrap = BO->hasNoSignedWrap();
1043 NoSignedWrap &= OpNoSignedWrap;
1044 if (NoSignedWrap != OpNoSignedWrap) {
1045 BO->setHasNoSignedWrap(NoSignedWrap);
1046 Worklist.Add(Ancestor);
1048 } else if (Ancestor->getOpcode() == Instruction::Trunc) {
1049 // The fact that the descaled input to the trunc has smaller absolute
1050 // value than the original input doesn't tell us anything useful about
1051 // the absolute values of the truncations.
1052 NoSignedWrap = false;
1054 assert((Ancestor->getOpcode() != Instruction::SExt || NoSignedWrap) &&
1055 "Failed to keep proper track of nsw flags while drilling down?");
1057 if (Ancestor == Val)
1058 // Got to the top, all done!
1061 // Move up one level in the expression.
1062 assert(Ancestor->hasOneUse() && "Drilled down when more than one use!");
1063 Ancestor = Ancestor->use_back();
1067 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
1068 SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
1070 if (Value *V = SimplifyGEPInst(Ops, TD))
1071 return ReplaceInstUsesWith(GEP, V);
1073 Value *PtrOp = GEP.getOperand(0);
1075 // Eliminate unneeded casts for indices, and replace indices which displace
1076 // by multiples of a zero size type with zero.
1078 bool MadeChange = false;
1079 Type *IntPtrTy = TD->getIntPtrType(GEP.getPointerOperandType());
1081 gep_type_iterator GTI = gep_type_begin(GEP);
1082 for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end();
1083 I != E; ++I, ++GTI) {
1084 // Skip indices into struct types.
1085 SequentialType *SeqTy = dyn_cast<SequentialType>(*GTI);
1086 if (!SeqTy) continue;
1088 // If the element type has zero size then any index over it is equivalent
1089 // to an index of zero, so replace it with zero if it is not zero already.
1090 if (SeqTy->getElementType()->isSized() &&
1091 TD->getTypeAllocSize(SeqTy->getElementType()) == 0)
1092 if (!isa<Constant>(*I) || !cast<Constant>(*I)->isNullValue()) {
1093 *I = Constant::getNullValue(IntPtrTy);
1097 Type *IndexTy = (*I)->getType();
1098 if (IndexTy != IntPtrTy) {
1099 // If we are using a wider index than needed for this platform, shrink
1100 // it to what we need. If narrower, sign-extend it to what we need.
1101 // This explicit cast can make subsequent optimizations more obvious.
1102 *I = Builder->CreateIntCast(*I, IntPtrTy, true);
1106 if (MadeChange) return &GEP;
1109 // Combine Indices - If the source pointer to this getelementptr instruction
1110 // is a getelementptr instruction, combine the indices of the two
1111 // getelementptr instructions into a single instruction.
1113 if (GEPOperator *Src = dyn_cast<GEPOperator>(PtrOp)) {
1114 if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
1117 // Note that if our source is a gep chain itself then we wait for that
1118 // chain to be resolved before we perform this transformation. This
1119 // avoids us creating a TON of code in some cases.
1120 if (GEPOperator *SrcGEP =
1121 dyn_cast<GEPOperator>(Src->getOperand(0)))
1122 if (SrcGEP->getNumOperands() == 2 && shouldMergeGEPs(*Src, *SrcGEP))
1123 return 0; // Wait until our source is folded to completion.
1125 SmallVector<Value*, 8> Indices;
1127 // Find out whether the last index in the source GEP is a sequential idx.
1128 bool EndsWithSequential = false;
1129 for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
1131 EndsWithSequential = !(*I)->isStructTy();
1133 // Can we combine the two pointer arithmetics offsets?
1134 if (EndsWithSequential) {
1135 // Replace: gep (gep %P, long B), long A, ...
1136 // With: T = long A+B; gep %P, T, ...
1139 Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
1140 Value *GO1 = GEP.getOperand(1);
1141 if (SO1 == Constant::getNullValue(SO1->getType())) {
1143 } else if (GO1 == Constant::getNullValue(GO1->getType())) {
1146 // If they aren't the same type, then the input hasn't been processed
1147 // by the loop above yet (which canonicalizes sequential index types to
1148 // intptr_t). Just avoid transforming this until the input has been
1150 if (SO1->getType() != GO1->getType())
1152 Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
1155 // Update the GEP in place if possible.
1156 if (Src->getNumOperands() == 2) {
1157 GEP.setOperand(0, Src->getOperand(0));
1158 GEP.setOperand(1, Sum);
1161 Indices.append(Src->op_begin()+1, Src->op_end()-1);
1162 Indices.push_back(Sum);
1163 Indices.append(GEP.op_begin()+2, GEP.op_end());
1164 } else if (isa<Constant>(*GEP.idx_begin()) &&
1165 cast<Constant>(*GEP.idx_begin())->isNullValue() &&
1166 Src->getNumOperands() != 1) {
1167 // Otherwise we can do the fold if the first index of the GEP is a zero
1168 Indices.append(Src->op_begin()+1, Src->op_end());
1169 Indices.append(GEP.idx_begin()+1, GEP.idx_end());
1172 if (!Indices.empty())
1173 return (GEP.isInBounds() && Src->isInBounds()) ?
1174 GetElementPtrInst::CreateInBounds(Src->getOperand(0), Indices,
1176 GetElementPtrInst::Create(Src->getOperand(0), Indices, GEP.getName());
1179 // Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
1180 Value *StrippedPtr = PtrOp->stripPointerCasts();
1181 PointerType *StrippedPtrTy = dyn_cast<PointerType>(StrippedPtr->getType());
1183 // We do not handle pointer-vector geps here.
1187 if (StrippedPtr != PtrOp &&
1188 StrippedPtrTy->getAddressSpace() == GEP.getPointerAddressSpace()) {
1190 bool HasZeroPointerIndex = false;
1191 if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
1192 HasZeroPointerIndex = C->isZero();
1194 // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
1195 // into : GEP [10 x i8]* X, i32 0, ...
1197 // Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
1198 // into : GEP i8* X, ...
1200 // This occurs when the program declares an array extern like "int X[];"
1201 if (HasZeroPointerIndex) {
1202 PointerType *CPTy = cast<PointerType>(PtrOp->getType());
1203 if (ArrayType *CATy =
1204 dyn_cast<ArrayType>(CPTy->getElementType())) {
1205 // GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
1206 if (CATy->getElementType() == StrippedPtrTy->getElementType()) {
1207 // -> GEP i8* X, ...
1208 SmallVector<Value*, 8> Idx(GEP.idx_begin()+1, GEP.idx_end());
1209 GetElementPtrInst *Res =
1210 GetElementPtrInst::Create(StrippedPtr, Idx, GEP.getName());
1211 Res->setIsInBounds(GEP.isInBounds());
1215 if (ArrayType *XATy =
1216 dyn_cast<ArrayType>(StrippedPtrTy->getElementType())){
1217 // GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
1218 if (CATy->getElementType() == XATy->getElementType()) {
1219 // -> GEP [10 x i8]* X, i32 0, ...
1220 // At this point, we know that the cast source type is a pointer
1221 // to an array of the same type as the destination pointer
1222 // array. Because the array type is never stepped over (there
1223 // is a leading zero) we can fold the cast into this GEP.
1224 GEP.setOperand(0, StrippedPtr);
1229 } else if (GEP.getNumOperands() == 2) {
1230 // Transform things like:
1231 // %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
1232 // into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
1233 Type *SrcElTy = StrippedPtrTy->getElementType();
1234 Type *ResElTy = PtrOp->getType()->getPointerElementType();
1235 if (TD && SrcElTy->isArrayTy() &&
1236 TD->getTypeAllocSize(SrcElTy->getArrayElementType()) ==
1237 TD->getTypeAllocSize(ResElTy)) {
1238 Type *IdxType = TD->getIntPtrType(GEP.getContext());
1239 Value *Idx[2] = { Constant::getNullValue(IdxType), GEP.getOperand(1) };
1240 Value *NewGEP = GEP.isInBounds() ?
1241 Builder->CreateInBoundsGEP(StrippedPtr, Idx, GEP.getName()) :
1242 Builder->CreateGEP(StrippedPtr, Idx, GEP.getName());
1243 // V and GEP are both pointer types --> BitCast
1244 return new BitCastInst(NewGEP, GEP.getType());
1247 // Transform things like:
1248 // %V = mul i64 %N, 4
1249 // %t = getelementptr i8* bitcast (i32* %arr to i8*), i32 %V
1250 // into: %t1 = getelementptr i32* %arr, i32 %N; bitcast
1251 if (TD && ResElTy->isSized() && SrcElTy->isSized()) {
1252 // Check that changing the type amounts to dividing the index by a scale
1254 uint64_t ResSize = TD->getTypeAllocSize(ResElTy);
1255 uint64_t SrcSize = TD->getTypeAllocSize(SrcElTy);
1256 if (ResSize && SrcSize % ResSize == 0) {
1257 Value *Idx = GEP.getOperand(1);
1258 unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
1259 uint64_t Scale = SrcSize / ResSize;
1261 // Earlier transforms ensure that the index has type IntPtrType, which
1262 // considerably simplifies the logic by eliminating implicit casts.
1263 assert(Idx->getType() == TD->getIntPtrType(GEP.getContext()) &&
1264 "Index not cast to pointer width?");
1267 if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
1268 // Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
1269 // If the multiplication NewIdx * Scale may overflow then the new
1270 // GEP may not be "inbounds".
1271 Value *NewGEP = GEP.isInBounds() && NSW ?
1272 Builder->CreateInBoundsGEP(StrippedPtr, NewIdx, GEP.getName()) :
1273 Builder->CreateGEP(StrippedPtr, NewIdx, GEP.getName());
1274 // The NewGEP must be pointer typed, so must the old one -> BitCast
1275 return new BitCastInst(NewGEP, GEP.getType());
1280 // Similarly, transform things like:
1281 // getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
1282 // (where tmp = 8*tmp2) into:
1283 // getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
1284 if (TD && ResElTy->isSized() && SrcElTy->isSized() &&
1285 SrcElTy->isArrayTy()) {
1286 // Check that changing to the array element type amounts to dividing the
1287 // index by a scale factor.
1288 uint64_t ResSize = TD->getTypeAllocSize(ResElTy);
1289 uint64_t ArrayEltSize
1290 = TD->getTypeAllocSize(SrcElTy->getArrayElementType());
1291 if (ResSize && ArrayEltSize % ResSize == 0) {
1292 Value *Idx = GEP.getOperand(1);
1293 unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
1294 uint64_t Scale = ArrayEltSize / ResSize;
1296 // Earlier transforms ensure that the index has type IntPtrType, which
1297 // considerably simplifies the logic by eliminating implicit casts.
1298 assert(Idx->getType() == TD->getIntPtrType(GEP.getContext()) &&
1299 "Index not cast to pointer width?");
1302 if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
1303 // Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
1304 // If the multiplication NewIdx * Scale may overflow then the new
1305 // GEP may not be "inbounds".
1307 Constant::getNullValue(TD->getIntPtrType(GEP.getContext())),
1311 Value *NewGEP = GEP.isInBounds() && NSW ?
1312 Builder->CreateInBoundsGEP(StrippedPtr, Off, GEP.getName()) :
1313 Builder->CreateGEP(StrippedPtr, Off, GEP.getName());
1314 // The NewGEP must be pointer typed, so must the old one -> BitCast
1315 return new BitCastInst(NewGEP, GEP.getType());
1325 /// See if we can simplify:
1326 /// X = bitcast A* to B*
1327 /// Y = gep X, <...constant indices...>
1328 /// into a gep of the original struct. This is important for SROA and alias
1329 /// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
1330 if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
1331 Value *Operand = BCI->getOperand(0);
1332 PointerType *OpType = cast<PointerType>(Operand->getType());
1333 unsigned OffsetBits = TD->getPointerSizeInBits();
1334 APInt Offset(OffsetBits, 0);
1335 if (!isa<BitCastInst>(Operand) &&
1336 GEP.accumulateConstantOffset(*TD, Offset) &&
1337 StrippedPtrTy->getAddressSpace() == GEP.getPointerAddressSpace()) {
1339 // If this GEP instruction doesn't move the pointer, just replace the GEP
1340 // with a bitcast of the real input to the dest type.
1342 // If the bitcast is of an allocation, and the allocation will be
1343 // converted to match the type of the cast, don't touch this.
1344 if (isa<AllocaInst>(Operand) || isAllocationFn(Operand, TLI)) {
1345 // See if the bitcast simplifies, if so, don't nuke this GEP yet.
1346 if (Instruction *I = visitBitCast(*BCI)) {
1349 BCI->getParent()->getInstList().insert(BCI, I);
1350 ReplaceInstUsesWith(*BCI, I);
1355 return new BitCastInst(Operand, GEP.getType());
1358 // Otherwise, if the offset is non-zero, we need to find out if there is a
1359 // field at Offset in 'A's type. If so, we can pull the cast through the
1361 SmallVector<Value*, 8> NewIndices;
1362 Type *InTy = OpType->getElementType();
1363 if (FindElementAtOffset(InTy, Offset.getSExtValue(), NewIndices)) {
1364 Value *NGEP = GEP.isInBounds() ?
1365 Builder->CreateInBoundsGEP(Operand, NewIndices) :
1366 Builder->CreateGEP(Operand, NewIndices);
1368 if (NGEP->getType() == GEP.getType())
1369 return ReplaceInstUsesWith(GEP, NGEP);
1370 NGEP->takeName(&GEP);
1371 return new BitCastInst(NGEP, GEP.getType());
1380 isAllocSiteRemovable(Instruction *AI, SmallVectorImpl<WeakVH> &Users,
1381 const TargetLibraryInfo *TLI) {
1382 SmallVector<Instruction*, 4> Worklist;
1383 Worklist.push_back(AI);
1386 Instruction *PI = Worklist.pop_back_val();
1387 for (Value::use_iterator UI = PI->use_begin(), UE = PI->use_end(); UI != UE;
1389 Instruction *I = cast<Instruction>(*UI);
1390 switch (I->getOpcode()) {
1392 // Give up the moment we see something we can't handle.
1395 case Instruction::BitCast:
1396 case Instruction::GetElementPtr:
1398 Worklist.push_back(I);
1401 case Instruction::ICmp: {
1402 ICmpInst *ICI = cast<ICmpInst>(I);
1403 // We can fold eq/ne comparisons with null to false/true, respectively.
1404 if (!ICI->isEquality() || !isa<ConstantPointerNull>(ICI->getOperand(1)))
1410 case Instruction::Call:
1411 // Ignore no-op and store intrinsics.
1412 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1413 switch (II->getIntrinsicID()) {
1417 case Intrinsic::memmove:
1418 case Intrinsic::memcpy:
1419 case Intrinsic::memset: {
1420 MemIntrinsic *MI = cast<MemIntrinsic>(II);
1421 if (MI->isVolatile() || MI->getRawDest() != PI)
1425 case Intrinsic::dbg_declare:
1426 case Intrinsic::dbg_value:
1427 case Intrinsic::invariant_start:
1428 case Intrinsic::invariant_end:
1429 case Intrinsic::lifetime_start:
1430 case Intrinsic::lifetime_end:
1431 case Intrinsic::objectsize:
1437 if (isFreeCall(I, TLI)) {
1443 case Instruction::Store: {
1444 StoreInst *SI = cast<StoreInst>(I);
1445 if (SI->isVolatile() || SI->getPointerOperand() != PI)
1451 llvm_unreachable("missing a return?");
1453 } while (!Worklist.empty());
1457 Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
1458 // If we have a malloc call which is only used in any amount of comparisons
1459 // to null and free calls, delete the calls and replace the comparisons with
1460 // true or false as appropriate.
1461 SmallVector<WeakVH, 64> Users;
1462 if (isAllocSiteRemovable(&MI, Users, TLI)) {
1463 for (unsigned i = 0, e = Users.size(); i != e; ++i) {
1464 Instruction *I = cast_or_null<Instruction>(&*Users[i]);
1467 if (ICmpInst *C = dyn_cast<ICmpInst>(I)) {
1468 ReplaceInstUsesWith(*C,
1469 ConstantInt::get(Type::getInt1Ty(C->getContext()),
1470 C->isFalseWhenEqual()));
1471 } else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I)) {
1472 ReplaceInstUsesWith(*I, UndefValue::get(I->getType()));
1473 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1474 if (II->getIntrinsicID() == Intrinsic::objectsize) {
1475 ConstantInt *CI = cast<ConstantInt>(II->getArgOperand(1));
1476 uint64_t DontKnow = CI->isZero() ? -1ULL : 0;
1477 ReplaceInstUsesWith(*I, ConstantInt::get(I->getType(), DontKnow));
1480 EraseInstFromFunction(*I);
1483 if (InvokeInst *II = dyn_cast<InvokeInst>(&MI)) {
1484 // Replace invoke with a NOP intrinsic to maintain the original CFG
1485 Module *M = II->getParent()->getParent()->getParent();
1486 Function *F = Intrinsic::getDeclaration(M, Intrinsic::donothing);
1487 InvokeInst::Create(F, II->getNormalDest(), II->getUnwindDest(),
1488 None, "", II->getParent());
1490 return EraseInstFromFunction(MI);
1495 /// \brief Move the call to free before a NULL test.
1497 /// Check if this free is accessed after its argument has been test
1498 /// against NULL (property 0).
1499 /// If yes, it is legal to move this call in its predecessor block.
1501 /// The move is performed only if the block containing the call to free
1502 /// will be removed, i.e.:
1503 /// 1. it has only one predecessor P, and P has two successors
1504 /// 2. it contains the call and an unconditional branch
1505 /// 3. its successor is the same as its predecessor's successor
1507 /// The profitability is out-of concern here and this function should
1508 /// be called only if the caller knows this transformation would be
1509 /// profitable (e.g., for code size).
1510 static Instruction *
1511 tryToMoveFreeBeforeNullTest(CallInst &FI) {
1512 Value *Op = FI.getArgOperand(0);
1513 BasicBlock *FreeInstrBB = FI.getParent();
1514 BasicBlock *PredBB = FreeInstrBB->getSinglePredecessor();
1516 // Validate part of constraint #1: Only one predecessor
1517 // FIXME: We can extend the number of predecessor, but in that case, we
1518 // would duplicate the call to free in each predecessor and it may
1519 // not be profitable even for code size.
1523 // Validate constraint #2: Does this block contains only the call to
1524 // free and an unconditional branch?
1525 // FIXME: We could check if we can speculate everything in the
1526 // predecessor block
1527 if (FreeInstrBB->size() != 2)
1530 if (!match(FreeInstrBB->getTerminator(), m_UnconditionalBr(SuccBB)))
1533 // Validate the rest of constraint #1 by matching on the pred branch.
1534 TerminatorInst *TI = PredBB->getTerminator();
1535 BasicBlock *TrueBB, *FalseBB;
1536 ICmpInst::Predicate Pred;
1537 if (!match(TI, m_Br(m_ICmp(Pred, m_Specific(Op), m_Zero()), TrueBB, FalseBB)))
1539 if (Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)
1542 // Validate constraint #3: Ensure the null case just falls through.
1543 if (SuccBB != (Pred == ICmpInst::ICMP_EQ ? TrueBB : FalseBB))
1545 assert(FreeInstrBB == (Pred == ICmpInst::ICMP_EQ ? FalseBB : TrueBB) &&
1546 "Broken CFG: missing edge from predecessor to successor");
1553 Instruction *InstCombiner::visitFree(CallInst &FI) {
1554 Value *Op = FI.getArgOperand(0);
1556 // free undef -> unreachable.
1557 if (isa<UndefValue>(Op)) {
1558 // Insert a new store to null because we cannot modify the CFG here.
1559 Builder->CreateStore(ConstantInt::getTrue(FI.getContext()),
1560 UndefValue::get(Type::getInt1PtrTy(FI.getContext())));
1561 return EraseInstFromFunction(FI);
1564 // If we have 'free null' delete the instruction. This can happen in stl code
1565 // when lots of inlining happens.
1566 if (isa<ConstantPointerNull>(Op))
1567 return EraseInstFromFunction(FI);
1569 // If we optimize for code size, try to move the call to free before the null
1570 // test so that simplify cfg can remove the empty block and dead code
1571 // elimination the branch. I.e., helps to turn something like:
1572 // if (foo) free(foo);
1576 if (Instruction *I = tryToMoveFreeBeforeNullTest(FI))
1584 Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
1585 // Change br (not X), label True, label False to: br X, label False, True
1587 BasicBlock *TrueDest;
1588 BasicBlock *FalseDest;
1589 if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) &&
1590 !isa<Constant>(X)) {
1591 // Swap Destinations and condition...
1593 BI.swapSuccessors();
1597 // Cannonicalize fcmp_one -> fcmp_oeq
1598 FCmpInst::Predicate FPred; Value *Y;
1599 if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)),
1600 TrueDest, FalseDest)) &&
1601 BI.getCondition()->hasOneUse())
1602 if (FPred == FCmpInst::FCMP_ONE || FPred == FCmpInst::FCMP_OLE ||
1603 FPred == FCmpInst::FCMP_OGE) {
1604 FCmpInst *Cond = cast<FCmpInst>(BI.getCondition());
1605 Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
1607 // Swap Destinations and condition.
1608 BI.swapSuccessors();
1613 // Cannonicalize icmp_ne -> icmp_eq
1614 ICmpInst::Predicate IPred;
1615 if (match(&BI, m_Br(m_ICmp(IPred, m_Value(X), m_Value(Y)),
1616 TrueDest, FalseDest)) &&
1617 BI.getCondition()->hasOneUse())
1618 if (IPred == ICmpInst::ICMP_NE || IPred == ICmpInst::ICMP_ULE ||
1619 IPred == ICmpInst::ICMP_SLE || IPred == ICmpInst::ICMP_UGE ||
1620 IPred == ICmpInst::ICMP_SGE) {
1621 ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
1622 Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
1623 // Swap Destinations and condition.
1624 BI.swapSuccessors();
1632 Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
1633 Value *Cond = SI.getCondition();
1634 if (Instruction *I = dyn_cast<Instruction>(Cond)) {
1635 if (I->getOpcode() == Instruction::Add)
1636 if (ConstantInt *AddRHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
1637 // change 'switch (X+4) case 1:' into 'switch (X) case -3'
1638 // Skip the first item since that's the default case.
1639 for (SwitchInst::CaseIt i = SI.case_begin(), e = SI.case_end();
1641 ConstantInt* CaseVal = i.getCaseValue();
1642 Constant* NewCaseVal = ConstantExpr::getSub(cast<Constant>(CaseVal),
1644 assert(isa<ConstantInt>(NewCaseVal) &&
1645 "Result of expression should be constant");
1646 i.setValue(cast<ConstantInt>(NewCaseVal));
1648 SI.setCondition(I->getOperand(0));
1656 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
1657 Value *Agg = EV.getAggregateOperand();
1659 if (!EV.hasIndices())
1660 return ReplaceInstUsesWith(EV, Agg);
1662 if (Constant *C = dyn_cast<Constant>(Agg)) {
1663 if (Constant *C2 = C->getAggregateElement(*EV.idx_begin())) {
1664 if (EV.getNumIndices() == 0)
1665 return ReplaceInstUsesWith(EV, C2);
1666 // Extract the remaining indices out of the constant indexed by the
1668 return ExtractValueInst::Create(C2, EV.getIndices().slice(1));
1670 return 0; // Can't handle other constants
1673 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
1674 // We're extracting from an insertvalue instruction, compare the indices
1675 const unsigned *exti, *exte, *insi, *inse;
1676 for (exti = EV.idx_begin(), insi = IV->idx_begin(),
1677 exte = EV.idx_end(), inse = IV->idx_end();
1678 exti != exte && insi != inse;
1681 // The insert and extract both reference distinctly different elements.
1682 // This means the extract is not influenced by the insert, and we can
1683 // replace the aggregate operand of the extract with the aggregate
1684 // operand of the insert. i.e., replace
1685 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
1686 // %E = extractvalue { i32, { i32 } } %I, 0
1688 // %E = extractvalue { i32, { i32 } } %A, 0
1689 return ExtractValueInst::Create(IV->getAggregateOperand(),
1692 if (exti == exte && insi == inse)
1693 // Both iterators are at the end: Index lists are identical. Replace
1694 // %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
1695 // %C = extractvalue { i32, { i32 } } %B, 1, 0
1697 return ReplaceInstUsesWith(EV, IV->getInsertedValueOperand());
1699 // The extract list is a prefix of the insert list. i.e. replace
1700 // %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
1701 // %E = extractvalue { i32, { i32 } } %I, 1
1703 // %X = extractvalue { i32, { i32 } } %A, 1
1704 // %E = insertvalue { i32 } %X, i32 42, 0
1705 // by switching the order of the insert and extract (though the
1706 // insertvalue should be left in, since it may have other uses).
1707 Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(),
1709 return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
1710 makeArrayRef(insi, inse));
1713 // The insert list is a prefix of the extract list
1714 // We can simply remove the common indices from the extract and make it
1715 // operate on the inserted value instead of the insertvalue result.
1717 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
1718 // %E = extractvalue { i32, { i32 } } %I, 1, 0
1720 // %E extractvalue { i32 } { i32 42 }, 0
1721 return ExtractValueInst::Create(IV->getInsertedValueOperand(),
1722 makeArrayRef(exti, exte));
1724 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
1725 // We're extracting from an intrinsic, see if we're the only user, which
1726 // allows us to simplify multiple result intrinsics to simpler things that
1727 // just get one value.
1728 if (II->hasOneUse()) {
1729 // Check if we're grabbing the overflow bit or the result of a 'with
1730 // overflow' intrinsic. If it's the latter we can remove the intrinsic
1731 // and replace it with a traditional binary instruction.
1732 switch (II->getIntrinsicID()) {
1733 case Intrinsic::uadd_with_overflow:
1734 case Intrinsic::sadd_with_overflow:
1735 if (*EV.idx_begin() == 0) { // Normal result.
1736 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1737 ReplaceInstUsesWith(*II, UndefValue::get(II->getType()));
1738 EraseInstFromFunction(*II);
1739 return BinaryOperator::CreateAdd(LHS, RHS);
1742 // If the normal result of the add is dead, and the RHS is a constant,
1743 // we can transform this into a range comparison.
1744 // overflow = uadd a, -4 --> overflow = icmp ugt a, 3
1745 if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow)
1746 if (ConstantInt *CI = dyn_cast<ConstantInt>(II->getArgOperand(1)))
1747 return new ICmpInst(ICmpInst::ICMP_UGT, II->getArgOperand(0),
1748 ConstantExpr::getNot(CI));
1750 case Intrinsic::usub_with_overflow:
1751 case Intrinsic::ssub_with_overflow:
1752 if (*EV.idx_begin() == 0) { // Normal result.
1753 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1754 ReplaceInstUsesWith(*II, UndefValue::get(II->getType()));
1755 EraseInstFromFunction(*II);
1756 return BinaryOperator::CreateSub(LHS, RHS);
1759 case Intrinsic::umul_with_overflow:
1760 case Intrinsic::smul_with_overflow:
1761 if (*EV.idx_begin() == 0) { // Normal result.
1762 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1763 ReplaceInstUsesWith(*II, UndefValue::get(II->getType()));
1764 EraseInstFromFunction(*II);
1765 return BinaryOperator::CreateMul(LHS, RHS);
1773 if (LoadInst *L = dyn_cast<LoadInst>(Agg))
1774 // If the (non-volatile) load only has one use, we can rewrite this to a
1775 // load from a GEP. This reduces the size of the load.
1776 // FIXME: If a load is used only by extractvalue instructions then this
1777 // could be done regardless of having multiple uses.
1778 if (L->isSimple() && L->hasOneUse()) {
1779 // extractvalue has integer indices, getelementptr has Value*s. Convert.
1780 SmallVector<Value*, 4> Indices;
1781 // Prefix an i32 0 since we need the first element.
1782 Indices.push_back(Builder->getInt32(0));
1783 for (ExtractValueInst::idx_iterator I = EV.idx_begin(), E = EV.idx_end();
1785 Indices.push_back(Builder->getInt32(*I));
1787 // We need to insert these at the location of the old load, not at that of
1788 // the extractvalue.
1789 Builder->SetInsertPoint(L->getParent(), L);
1790 Value *GEP = Builder->CreateInBoundsGEP(L->getPointerOperand(), Indices);
1791 // Returning the load directly will cause the main loop to insert it in
1792 // the wrong spot, so use ReplaceInstUsesWith().
1793 return ReplaceInstUsesWith(EV, Builder->CreateLoad(GEP));
1795 // We could simplify extracts from other values. Note that nested extracts may
1796 // already be simplified implicitly by the above: extract (extract (insert) )
1797 // will be translated into extract ( insert ( extract ) ) first and then just
1798 // the value inserted, if appropriate. Similarly for extracts from single-use
1799 // loads: extract (extract (load)) will be translated to extract (load (gep))
1800 // and if again single-use then via load (gep (gep)) to load (gep).
1801 // However, double extracts from e.g. function arguments or return values
1802 // aren't handled yet.
1806 enum Personality_Type {
1807 Unknown_Personality,
1808 GNU_Ada_Personality,
1809 GNU_CXX_Personality,
1810 GNU_ObjC_Personality
1813 /// RecognizePersonality - See if the given exception handling personality
1814 /// function is one that we understand. If so, return a description of it;
1815 /// otherwise return Unknown_Personality.
1816 static Personality_Type RecognizePersonality(Value *Pers) {
1817 Function *F = dyn_cast<Function>(Pers->stripPointerCasts());
1819 return Unknown_Personality;
1820 return StringSwitch<Personality_Type>(F->getName())
1821 .Case("__gnat_eh_personality", GNU_Ada_Personality)
1822 .Case("__gxx_personality_v0", GNU_CXX_Personality)
1823 .Case("__objc_personality_v0", GNU_ObjC_Personality)
1824 .Default(Unknown_Personality);
1827 /// isCatchAll - Return 'true' if the given typeinfo will match anything.
1828 static bool isCatchAll(Personality_Type Personality, Constant *TypeInfo) {
1829 switch (Personality) {
1830 case Unknown_Personality:
1832 case GNU_Ada_Personality:
1833 // While __gnat_all_others_value will match any Ada exception, it doesn't
1834 // match foreign exceptions (or didn't, before gcc-4.7).
1836 case GNU_CXX_Personality:
1837 case GNU_ObjC_Personality:
1838 return TypeInfo->isNullValue();
1840 llvm_unreachable("Unknown personality!");
1843 static bool shorter_filter(const Value *LHS, const Value *RHS) {
1845 cast<ArrayType>(LHS->getType())->getNumElements()
1847 cast<ArrayType>(RHS->getType())->getNumElements();
1850 Instruction *InstCombiner::visitLandingPadInst(LandingPadInst &LI) {
1851 // The logic here should be correct for any real-world personality function.
1852 // However if that turns out not to be true, the offending logic can always
1853 // be conditioned on the personality function, like the catch-all logic is.
1854 Personality_Type Personality = RecognizePersonality(LI.getPersonalityFn());
1856 // Simplify the list of clauses, eg by removing repeated catch clauses
1857 // (these are often created by inlining).
1858 bool MakeNewInstruction = false; // If true, recreate using the following:
1859 SmallVector<Value *, 16> NewClauses; // - Clauses for the new instruction;
1860 bool CleanupFlag = LI.isCleanup(); // - The new instruction is a cleanup.
1862 SmallPtrSet<Value *, 16> AlreadyCaught; // Typeinfos known caught already.
1863 for (unsigned i = 0, e = LI.getNumClauses(); i != e; ++i) {
1864 bool isLastClause = i + 1 == e;
1865 if (LI.isCatch(i)) {
1867 Value *CatchClause = LI.getClause(i);
1868 Constant *TypeInfo = cast<Constant>(CatchClause->stripPointerCasts());
1870 // If we already saw this clause, there is no point in having a second
1872 if (AlreadyCaught.insert(TypeInfo)) {
1873 // This catch clause was not already seen.
1874 NewClauses.push_back(CatchClause);
1876 // Repeated catch clause - drop the redundant copy.
1877 MakeNewInstruction = true;
1880 // If this is a catch-all then there is no point in keeping any following
1881 // clauses or marking the landingpad as having a cleanup.
1882 if (isCatchAll(Personality, TypeInfo)) {
1884 MakeNewInstruction = true;
1885 CleanupFlag = false;
1889 // A filter clause. If any of the filter elements were already caught
1890 // then they can be dropped from the filter. It is tempting to try to
1891 // exploit the filter further by saying that any typeinfo that does not
1892 // occur in the filter can't be caught later (and thus can be dropped).
1893 // However this would be wrong, since typeinfos can match without being
1894 // equal (for example if one represents a C++ class, and the other some
1895 // class derived from it).
1896 assert(LI.isFilter(i) && "Unsupported landingpad clause!");
1897 Value *FilterClause = LI.getClause(i);
1898 ArrayType *FilterType = cast<ArrayType>(FilterClause->getType());
1899 unsigned NumTypeInfos = FilterType->getNumElements();
1901 // An empty filter catches everything, so there is no point in keeping any
1902 // following clauses or marking the landingpad as having a cleanup. By
1903 // dealing with this case here the following code is made a bit simpler.
1904 if (!NumTypeInfos) {
1905 NewClauses.push_back(FilterClause);
1907 MakeNewInstruction = true;
1908 CleanupFlag = false;
1912 bool MakeNewFilter = false; // If true, make a new filter.
1913 SmallVector<Constant *, 16> NewFilterElts; // New elements.
1914 if (isa<ConstantAggregateZero>(FilterClause)) {
1915 // Not an empty filter - it contains at least one null typeinfo.
1916 assert(NumTypeInfos > 0 && "Should have handled empty filter already!");
1917 Constant *TypeInfo =
1918 Constant::getNullValue(FilterType->getElementType());
1919 // If this typeinfo is a catch-all then the filter can never match.
1920 if (isCatchAll(Personality, TypeInfo)) {
1921 // Throw the filter away.
1922 MakeNewInstruction = true;
1926 // There is no point in having multiple copies of this typeinfo, so
1927 // discard all but the first copy if there is more than one.
1928 NewFilterElts.push_back(TypeInfo);
1929 if (NumTypeInfos > 1)
1930 MakeNewFilter = true;
1932 ConstantArray *Filter = cast<ConstantArray>(FilterClause);
1933 SmallPtrSet<Value *, 16> SeenInFilter; // For uniquing the elements.
1934 NewFilterElts.reserve(NumTypeInfos);
1936 // Remove any filter elements that were already caught or that already
1937 // occurred in the filter. While there, see if any of the elements are
1938 // catch-alls. If so, the filter can be discarded.
1939 bool SawCatchAll = false;
1940 for (unsigned j = 0; j != NumTypeInfos; ++j) {
1941 Value *Elt = Filter->getOperand(j);
1942 Constant *TypeInfo = cast<Constant>(Elt->stripPointerCasts());
1943 if (isCatchAll(Personality, TypeInfo)) {
1944 // This element is a catch-all. Bail out, noting this fact.
1948 if (AlreadyCaught.count(TypeInfo))
1949 // Already caught by an earlier clause, so having it in the filter
1952 // There is no point in having multiple copies of the same typeinfo in
1953 // a filter, so only add it if we didn't already.
1954 if (SeenInFilter.insert(TypeInfo))
1955 NewFilterElts.push_back(cast<Constant>(Elt));
1957 // A filter containing a catch-all cannot match anything by definition.
1959 // Throw the filter away.
1960 MakeNewInstruction = true;
1964 // If we dropped something from the filter, make a new one.
1965 if (NewFilterElts.size() < NumTypeInfos)
1966 MakeNewFilter = true;
1968 if (MakeNewFilter) {
1969 FilterType = ArrayType::get(FilterType->getElementType(),
1970 NewFilterElts.size());
1971 FilterClause = ConstantArray::get(FilterType, NewFilterElts);
1972 MakeNewInstruction = true;
1975 NewClauses.push_back(FilterClause);
1977 // If the new filter is empty then it will catch everything so there is
1978 // no point in keeping any following clauses or marking the landingpad
1979 // as having a cleanup. The case of the original filter being empty was
1980 // already handled above.
1981 if (MakeNewFilter && !NewFilterElts.size()) {
1982 assert(MakeNewInstruction && "New filter but not a new instruction!");
1983 CleanupFlag = false;
1989 // If several filters occur in a row then reorder them so that the shortest
1990 // filters come first (those with the smallest number of elements). This is
1991 // advantageous because shorter filters are more likely to match, speeding up
1992 // unwinding, but mostly because it increases the effectiveness of the other
1993 // filter optimizations below.
1994 for (unsigned i = 0, e = NewClauses.size(); i + 1 < e; ) {
1996 // Find the maximal 'j' s.t. the range [i, j) consists entirely of filters.
1997 for (j = i; j != e; ++j)
1998 if (!isa<ArrayType>(NewClauses[j]->getType()))
2001 // Check whether the filters are already sorted by length. We need to know
2002 // if sorting them is actually going to do anything so that we only make a
2003 // new landingpad instruction if it does.
2004 for (unsigned k = i; k + 1 < j; ++k)
2005 if (shorter_filter(NewClauses[k+1], NewClauses[k])) {
2006 // Not sorted, so sort the filters now. Doing an unstable sort would be
2007 // correct too but reordering filters pointlessly might confuse users.
2008 std::stable_sort(NewClauses.begin() + i, NewClauses.begin() + j,
2010 MakeNewInstruction = true;
2014 // Look for the next batch of filters.
2018 // If typeinfos matched if and only if equal, then the elements of a filter L
2019 // that occurs later than a filter F could be replaced by the intersection of
2020 // the elements of F and L. In reality two typeinfos can match without being
2021 // equal (for example if one represents a C++ class, and the other some class
2022 // derived from it) so it would be wrong to perform this transform in general.
2023 // However the transform is correct and useful if F is a subset of L. In that
2024 // case L can be replaced by F, and thus removed altogether since repeating a
2025 // filter is pointless. So here we look at all pairs of filters F and L where
2026 // L follows F in the list of clauses, and remove L if every element of F is
2027 // an element of L. This can occur when inlining C++ functions with exception
2029 for (unsigned i = 0; i + 1 < NewClauses.size(); ++i) {
2030 // Examine each filter in turn.
2031 Value *Filter = NewClauses[i];
2032 ArrayType *FTy = dyn_cast<ArrayType>(Filter->getType());
2034 // Not a filter - skip it.
2036 unsigned FElts = FTy->getNumElements();
2037 // Examine each filter following this one. Doing this backwards means that
2038 // we don't have to worry about filters disappearing under us when removed.
2039 for (unsigned j = NewClauses.size() - 1; j != i; --j) {
2040 Value *LFilter = NewClauses[j];
2041 ArrayType *LTy = dyn_cast<ArrayType>(LFilter->getType());
2043 // Not a filter - skip it.
2045 // If Filter is a subset of LFilter, i.e. every element of Filter is also
2046 // an element of LFilter, then discard LFilter.
2047 SmallVectorImpl<Value *>::iterator J = NewClauses.begin() + j;
2048 // If Filter is empty then it is a subset of LFilter.
2051 NewClauses.erase(J);
2052 MakeNewInstruction = true;
2053 // Move on to the next filter.
2056 unsigned LElts = LTy->getNumElements();
2057 // If Filter is longer than LFilter then it cannot be a subset of it.
2059 // Move on to the next filter.
2061 // At this point we know that LFilter has at least one element.
2062 if (isa<ConstantAggregateZero>(LFilter)) { // LFilter only contains zeros.
2063 // Filter is a subset of LFilter iff Filter contains only zeros (as we
2064 // already know that Filter is not longer than LFilter).
2065 if (isa<ConstantAggregateZero>(Filter)) {
2066 assert(FElts <= LElts && "Should have handled this case earlier!");
2068 NewClauses.erase(J);
2069 MakeNewInstruction = true;
2071 // Move on to the next filter.
2074 ConstantArray *LArray = cast<ConstantArray>(LFilter);
2075 if (isa<ConstantAggregateZero>(Filter)) { // Filter only contains zeros.
2076 // Since Filter is non-empty and contains only zeros, it is a subset of
2077 // LFilter iff LFilter contains a zero.
2078 assert(FElts > 0 && "Should have eliminated the empty filter earlier!");
2079 for (unsigned l = 0; l != LElts; ++l)
2080 if (LArray->getOperand(l)->isNullValue()) {
2081 // LFilter contains a zero - discard it.
2082 NewClauses.erase(J);
2083 MakeNewInstruction = true;
2086 // Move on to the next filter.
2089 // At this point we know that both filters are ConstantArrays. Loop over
2090 // operands to see whether every element of Filter is also an element of
2091 // LFilter. Since filters tend to be short this is probably faster than
2092 // using a method that scales nicely.
2093 ConstantArray *FArray = cast<ConstantArray>(Filter);
2094 bool AllFound = true;
2095 for (unsigned f = 0; f != FElts; ++f) {
2096 Value *FTypeInfo = FArray->getOperand(f)->stripPointerCasts();
2098 for (unsigned l = 0; l != LElts; ++l) {
2099 Value *LTypeInfo = LArray->getOperand(l)->stripPointerCasts();
2100 if (LTypeInfo == FTypeInfo) {
2110 NewClauses.erase(J);
2111 MakeNewInstruction = true;
2113 // Move on to the next filter.
2117 // If we changed any of the clauses, replace the old landingpad instruction
2119 if (MakeNewInstruction) {
2120 LandingPadInst *NLI = LandingPadInst::Create(LI.getType(),
2121 LI.getPersonalityFn(),
2123 for (unsigned i = 0, e = NewClauses.size(); i != e; ++i)
2124 NLI->addClause(NewClauses[i]);
2125 // A landing pad with no clauses must have the cleanup flag set. It is
2126 // theoretically possible, though highly unlikely, that we eliminated all
2127 // clauses. If so, force the cleanup flag to true.
2128 if (NewClauses.empty())
2130 NLI->setCleanup(CleanupFlag);
2134 // Even if none of the clauses changed, we may nonetheless have understood
2135 // that the cleanup flag is pointless. Clear it if so.
2136 if (LI.isCleanup() != CleanupFlag) {
2137 assert(!CleanupFlag && "Adding a cleanup, not removing one?!");
2138 LI.setCleanup(CleanupFlag);
2148 /// TryToSinkInstruction - Try to move the specified instruction from its
2149 /// current block into the beginning of DestBlock, which can only happen if it's
2150 /// safe to move the instruction past all of the instructions between it and the
2151 /// end of its block.
2152 static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
2153 assert(I->hasOneUse() && "Invariants didn't hold!");
2155 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
2156 if (isa<PHINode>(I) || isa<LandingPadInst>(I) || I->mayHaveSideEffects() ||
2157 isa<TerminatorInst>(I))
2160 // Do not sink alloca instructions out of the entry block.
2161 if (isa<AllocaInst>(I) && I->getParent() ==
2162 &DestBlock->getParent()->getEntryBlock())
2165 // We can only sink load instructions if there is nothing between the load and
2166 // the end of block that could change the value.
2167 if (I->mayReadFromMemory()) {
2168 for (BasicBlock::iterator Scan = I, E = I->getParent()->end();
2170 if (Scan->mayWriteToMemory())
2174 BasicBlock::iterator InsertPos = DestBlock->getFirstInsertionPt();
2175 I->moveBefore(InsertPos);
2181 /// AddReachableCodeToWorklist - Walk the function in depth-first order, adding
2182 /// all reachable code to the worklist.
2184 /// This has a couple of tricks to make the code faster and more powerful. In
2185 /// particular, we constant fold and DCE instructions as we go, to avoid adding
2186 /// them to the worklist (this significantly speeds up instcombine on code where
2187 /// many instructions are dead or constant). Additionally, if we find a branch
2188 /// whose condition is a known constant, we only visit the reachable successors.
2190 static bool AddReachableCodeToWorklist(BasicBlock *BB,
2191 SmallPtrSet<BasicBlock*, 64> &Visited,
2193 const DataLayout *TD,
2194 const TargetLibraryInfo *TLI) {
2195 bool MadeIRChange = false;
2196 SmallVector<BasicBlock*, 256> Worklist;
2197 Worklist.push_back(BB);
2199 SmallVector<Instruction*, 128> InstrsForInstCombineWorklist;
2200 DenseMap<ConstantExpr*, Constant*> FoldedConstants;
2203 BB = Worklist.pop_back_val();
2205 // We have now visited this block! If we've already been here, ignore it.
2206 if (!Visited.insert(BB)) continue;
2208 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) {
2209 Instruction *Inst = BBI++;
2211 // DCE instruction if trivially dead.
2212 if (isInstructionTriviallyDead(Inst, TLI)) {
2214 DEBUG(errs() << "IC: DCE: " << *Inst << '\n');
2215 Inst->eraseFromParent();
2219 // ConstantProp instruction if trivially constant.
2220 if (!Inst->use_empty() && isa<Constant>(Inst->getOperand(0)))
2221 if (Constant *C = ConstantFoldInstruction(Inst, TD, TLI)) {
2222 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: "
2224 Inst->replaceAllUsesWith(C);
2226 Inst->eraseFromParent();
2231 // See if we can constant fold its operands.
2232 for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end();
2234 ConstantExpr *CE = dyn_cast<ConstantExpr>(i);
2235 if (CE == 0) continue;
2237 Constant*& FoldRes = FoldedConstants[CE];
2239 FoldRes = ConstantFoldConstantExpression(CE, TD, TLI);
2243 if (FoldRes != CE) {
2245 MadeIRChange = true;
2250 InstrsForInstCombineWorklist.push_back(Inst);
2253 // Recursively visit successors. If this is a branch or switch on a
2254 // constant, only visit the reachable successor.
2255 TerminatorInst *TI = BB->getTerminator();
2256 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2257 if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
2258 bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
2259 BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
2260 Worklist.push_back(ReachableBB);
2263 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2264 if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
2265 // See if this is an explicit destination.
2266 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2268 if (i.getCaseValue() == Cond) {
2269 BasicBlock *ReachableBB = i.getCaseSuccessor();
2270 Worklist.push_back(ReachableBB);
2274 // Otherwise it is the default destination.
2275 Worklist.push_back(SI->getDefaultDest());
2280 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
2281 Worklist.push_back(TI->getSuccessor(i));
2282 } while (!Worklist.empty());
2284 // Once we've found all of the instructions to add to instcombine's worklist,
2285 // add them in reverse order. This way instcombine will visit from the top
2286 // of the function down. This jives well with the way that it adds all uses
2287 // of instructions to the worklist after doing a transformation, thus avoiding
2288 // some N^2 behavior in pathological cases.
2289 IC.Worklist.AddInitialGroup(&InstrsForInstCombineWorklist[0],
2290 InstrsForInstCombineWorklist.size());
2292 return MadeIRChange;
2295 bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {
2296 MadeIRChange = false;
2298 DEBUG(errs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on "
2299 << F.getName() << "\n");
2302 // Do a depth-first traversal of the function, populate the worklist with
2303 // the reachable instructions. Ignore blocks that are not reachable. Keep
2304 // track of which blocks we visit.
2305 SmallPtrSet<BasicBlock*, 64> Visited;
2306 MadeIRChange |= AddReachableCodeToWorklist(F.begin(), Visited, *this, TD,
2309 // Do a quick scan over the function. If we find any blocks that are
2310 // unreachable, remove any instructions inside of them. This prevents
2311 // the instcombine code from having to deal with some bad special cases.
2312 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
2313 if (Visited.count(BB)) continue;
2315 // Delete the instructions backwards, as it has a reduced likelihood of
2316 // having to update as many def-use and use-def chains.
2317 Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
2318 while (EndInst != BB->begin()) {
2319 // Delete the next to last instruction.
2320 BasicBlock::iterator I = EndInst;
2321 Instruction *Inst = --I;
2322 if (!Inst->use_empty())
2323 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
2324 if (isa<LandingPadInst>(Inst)) {
2328 if (!isa<DbgInfoIntrinsic>(Inst)) {
2330 MadeIRChange = true;
2332 Inst->eraseFromParent();
2337 while (!Worklist.isEmpty()) {
2338 Instruction *I = Worklist.RemoveOne();
2339 if (I == 0) continue; // skip null values.
2341 // Check to see if we can DCE the instruction.
2342 if (isInstructionTriviallyDead(I, TLI)) {
2343 DEBUG(errs() << "IC: DCE: " << *I << '\n');
2344 EraseInstFromFunction(*I);
2346 MadeIRChange = true;
2350 // Instruction isn't dead, see if we can constant propagate it.
2351 if (!I->use_empty() && isa<Constant>(I->getOperand(0)))
2352 if (Constant *C = ConstantFoldInstruction(I, TD, TLI)) {
2353 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *I << '\n');
2355 // Add operands to the worklist.
2356 ReplaceInstUsesWith(*I, C);
2358 EraseInstFromFunction(*I);
2359 MadeIRChange = true;
2363 // See if we can trivially sink this instruction to a successor basic block.
2364 if (I->hasOneUse()) {
2365 BasicBlock *BB = I->getParent();
2366 Instruction *UserInst = cast<Instruction>(I->use_back());
2367 BasicBlock *UserParent;
2369 // Get the block the use occurs in.
2370 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
2371 UserParent = PN->getIncomingBlock(I->use_begin().getUse());
2373 UserParent = UserInst->getParent();
2375 if (UserParent != BB) {
2376 bool UserIsSuccessor = false;
2377 // See if the user is one of our successors.
2378 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
2379 if (*SI == UserParent) {
2380 UserIsSuccessor = true;
2384 // If the user is one of our immediate successors, and if that successor
2385 // only has us as a predecessors (we'd have to split the critical edge
2386 // otherwise), we can keep going.
2387 if (UserIsSuccessor && UserParent->getSinglePredecessor())
2388 // Okay, the CFG is simple enough, try to sink this instruction.
2389 MadeIRChange |= TryToSinkInstruction(I, UserParent);
2393 // Now that we have an instruction, try combining it to simplify it.
2394 Builder->SetInsertPoint(I->getParent(), I);
2395 Builder->SetCurrentDebugLocation(I->getDebugLoc());
2400 DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
2401 DEBUG(errs() << "IC: Visiting: " << OrigI << '\n');
2403 if (Instruction *Result = visit(*I)) {
2405 // Should we replace the old instruction with a new one?
2407 DEBUG(errs() << "IC: Old = " << *I << '\n'
2408 << " New = " << *Result << '\n');
2410 if (!I->getDebugLoc().isUnknown())
2411 Result->setDebugLoc(I->getDebugLoc());
2412 // Everything uses the new instruction now.
2413 I->replaceAllUsesWith(Result);
2415 // Move the name to the new instruction first.
2416 Result->takeName(I);
2418 // Push the new instruction and any users onto the worklist.
2419 Worklist.Add(Result);
2420 Worklist.AddUsersToWorkList(*Result);
2422 // Insert the new instruction into the basic block...
2423 BasicBlock *InstParent = I->getParent();
2424 BasicBlock::iterator InsertPos = I;
2426 // If we replace a PHI with something that isn't a PHI, fix up the
2428 if (!isa<PHINode>(Result) && isa<PHINode>(InsertPos))
2429 InsertPos = InstParent->getFirstInsertionPt();
2431 InstParent->getInstList().insert(InsertPos, Result);
2433 EraseInstFromFunction(*I);
2436 DEBUG(errs() << "IC: Mod = " << OrigI << '\n'
2437 << " New = " << *I << '\n');
2440 // If the instruction was modified, it's possible that it is now dead.
2441 // if so, remove it.
2442 if (isInstructionTriviallyDead(I, TLI)) {
2443 EraseInstFromFunction(*I);
2446 Worklist.AddUsersToWorkList(*I);
2449 MadeIRChange = true;
2454 return MadeIRChange;
2458 class InstCombinerLibCallSimplifier : public LibCallSimplifier {
2461 InstCombinerLibCallSimplifier(const DataLayout *TD,
2462 const TargetLibraryInfo *TLI,
2464 : LibCallSimplifier(TD, TLI, UnsafeFPShrink) {
2468 /// replaceAllUsesWith - override so that instruction replacement
2469 /// can be defined in terms of the instruction combiner framework.
2470 virtual void replaceAllUsesWith(Instruction *I, Value *With) const {
2471 IC->ReplaceInstUsesWith(*I, With);
2476 bool InstCombiner::runOnFunction(Function &F) {
2477 TD = getAnalysisIfAvailable<DataLayout>();
2478 TLI = &getAnalysis<TargetLibraryInfo>();
2480 MinimizeSize = F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
2481 Attribute::MinSize);
2483 /// Builder - This is an IRBuilder that automatically inserts new
2484 /// instructions into the worklist when they are created.
2485 IRBuilder<true, TargetFolder, InstCombineIRInserter>
2486 TheBuilder(F.getContext(), TargetFolder(TD),
2487 InstCombineIRInserter(Worklist));
2488 Builder = &TheBuilder;
2490 InstCombinerLibCallSimplifier TheSimplifier(TD, TLI, this);
2491 Simplifier = &TheSimplifier;
2493 bool EverMadeChange = false;
2495 // Lower dbg.declare intrinsics otherwise their value may be clobbered
2497 EverMadeChange = LowerDbgDeclare(F);
2499 // Iterate while there is work to do.
2500 unsigned Iteration = 0;
2501 while (DoOneIteration(F, Iteration++))
2502 EverMadeChange = true;
2505 return EverMadeChange;
2508 FunctionPass *llvm::createInstructionCombiningPass() {
2509 return new InstCombiner();