1 //===- InstCombineSelect.cpp ----------------------------------------------===//
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 // This file implements the visitSelect function.
12 //===----------------------------------------------------------------------===//
14 #include "InstCombine.h"
15 #include "llvm/Support/PatternMatch.h"
16 #include "llvm/Analysis/ConstantFolding.h"
17 #include "llvm/Analysis/InstructionSimplify.h"
19 using namespace PatternMatch;
21 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
22 /// returning the kind and providing the out parameter results if we
23 /// successfully match.
24 static SelectPatternFlavor
25 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
26 SelectInst *SI = dyn_cast<SelectInst>(V);
27 if (SI == 0) return SPF_UNKNOWN;
29 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
30 if (ICI == 0) return SPF_UNKNOWN;
32 LHS = ICI->getOperand(0);
33 RHS = ICI->getOperand(1);
35 // (icmp X, Y) ? X : Y
36 if (SI->getTrueValue() == ICI->getOperand(0) &&
37 SI->getFalseValue() == ICI->getOperand(1)) {
38 switch (ICI->getPredicate()) {
39 default: return SPF_UNKNOWN; // Equality.
40 case ICmpInst::ICMP_UGT:
41 case ICmpInst::ICMP_UGE: return SPF_UMAX;
42 case ICmpInst::ICMP_SGT:
43 case ICmpInst::ICMP_SGE: return SPF_SMAX;
44 case ICmpInst::ICMP_ULT:
45 case ICmpInst::ICMP_ULE: return SPF_UMIN;
46 case ICmpInst::ICMP_SLT:
47 case ICmpInst::ICMP_SLE: return SPF_SMIN;
51 // (icmp X, Y) ? Y : X
52 if (SI->getTrueValue() == ICI->getOperand(1) &&
53 SI->getFalseValue() == ICI->getOperand(0)) {
54 switch (ICI->getPredicate()) {
55 default: return SPF_UNKNOWN; // Equality.
56 case ICmpInst::ICMP_UGT:
57 case ICmpInst::ICMP_UGE: return SPF_UMIN;
58 case ICmpInst::ICMP_SGT:
59 case ICmpInst::ICMP_SGE: return SPF_SMIN;
60 case ICmpInst::ICMP_ULT:
61 case ICmpInst::ICMP_ULE: return SPF_UMAX;
62 case ICmpInst::ICMP_SLT:
63 case ICmpInst::ICMP_SLE: return SPF_SMAX;
67 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
73 /// GetSelectFoldableOperands - We want to turn code that looks like this:
75 /// %D = select %cond, %C, %A
77 /// %C = select %cond, %B, 0
80 /// Assuming that the specified instruction is an operand to the select, return
81 /// a bitmask indicating which operands of this instruction are foldable if they
82 /// equal the other incoming value of the select.
84 static unsigned GetSelectFoldableOperands(Instruction *I) {
85 switch (I->getOpcode()) {
86 case Instruction::Add:
87 case Instruction::Mul:
88 case Instruction::And:
90 case Instruction::Xor:
91 return 3; // Can fold through either operand.
92 case Instruction::Sub: // Can only fold on the amount subtracted.
93 case Instruction::Shl: // Can only fold on the shift amount.
94 case Instruction::LShr:
95 case Instruction::AShr:
98 return 0; // Cannot fold
102 /// GetSelectFoldableConstant - For the same transformation as the previous
103 /// function, return the identity constant that goes into the select.
104 static Constant *GetSelectFoldableConstant(Instruction *I) {
105 switch (I->getOpcode()) {
106 default: llvm_unreachable("This cannot happen!");
107 case Instruction::Add:
108 case Instruction::Sub:
109 case Instruction::Or:
110 case Instruction::Xor:
111 case Instruction::Shl:
112 case Instruction::LShr:
113 case Instruction::AShr:
114 return Constant::getNullValue(I->getType());
115 case Instruction::And:
116 return Constant::getAllOnesValue(I->getType());
117 case Instruction::Mul:
118 return ConstantInt::get(I->getType(), 1);
122 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
123 /// have the same opcode and only one use each. Try to simplify this.
124 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
126 if (TI->getNumOperands() == 1) {
127 // If this is a non-volatile load or a cast from the same type,
130 if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
133 return 0; // unknown unary op.
136 // Fold this by inserting a select from the input values.
137 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
138 FI->getOperand(0), SI.getName()+".v");
139 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
143 // Only handle binary operators here.
144 if (!isa<BinaryOperator>(TI))
147 // Figure out if the operations have any operands in common.
148 Value *MatchOp, *OtherOpT, *OtherOpF;
150 if (TI->getOperand(0) == FI->getOperand(0)) {
151 MatchOp = TI->getOperand(0);
152 OtherOpT = TI->getOperand(1);
153 OtherOpF = FI->getOperand(1);
154 MatchIsOpZero = true;
155 } else if (TI->getOperand(1) == FI->getOperand(1)) {
156 MatchOp = TI->getOperand(1);
157 OtherOpT = TI->getOperand(0);
158 OtherOpF = FI->getOperand(0);
159 MatchIsOpZero = false;
160 } else if (!TI->isCommutative()) {
162 } else if (TI->getOperand(0) == FI->getOperand(1)) {
163 MatchOp = TI->getOperand(0);
164 OtherOpT = TI->getOperand(1);
165 OtherOpF = FI->getOperand(0);
166 MatchIsOpZero = true;
167 } else if (TI->getOperand(1) == FI->getOperand(0)) {
168 MatchOp = TI->getOperand(1);
169 OtherOpT = TI->getOperand(0);
170 OtherOpF = FI->getOperand(1);
171 MatchIsOpZero = true;
176 // If we reach here, they do have operations in common.
177 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
178 OtherOpF, SI.getName()+".v");
180 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
182 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
184 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
186 llvm_unreachable("Shouldn't get here");
190 static bool isSelect01(Constant *C1, Constant *C2) {
191 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
194 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
197 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
199 return C1I->isOne() || C1I->isAllOnesValue() ||
200 C2I->isOne() || C2I->isAllOnesValue();
203 /// FoldSelectIntoOp - Try fold the select into one of the operands to
204 /// facilitate further optimization.
205 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
207 // See the comment above GetSelectFoldableOperands for a description of the
208 // transformation we are doing here.
209 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
210 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
211 !isa<Constant>(FalseVal)) {
212 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
213 unsigned OpToFold = 0;
214 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
216 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
221 Constant *C = GetSelectFoldableConstant(TVI);
222 Value *OOp = TVI->getOperand(2-OpToFold);
223 // Avoid creating select between 2 constants unless it's selecting
224 // between 0, 1 and -1.
225 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
226 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
227 NewSel->takeName(TVI);
228 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
229 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
231 if (isa<PossiblyExactOperator>(BO))
232 BO->setIsExact(TVI_BO->isExact());
233 if (isa<OverflowingBinaryOperator>(BO)) {
234 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
235 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
244 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
245 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
246 !isa<Constant>(TrueVal)) {
247 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
248 unsigned OpToFold = 0;
249 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
251 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
256 Constant *C = GetSelectFoldableConstant(FVI);
257 Value *OOp = FVI->getOperand(2-OpToFold);
258 // Avoid creating select between 2 constants unless it's selecting
259 // between 0, 1 and -1.
260 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
261 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
262 NewSel->takeName(FVI);
263 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
264 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
266 if (isa<PossiblyExactOperator>(BO))
267 BO->setIsExact(FVI_BO->isExact());
268 if (isa<OverflowingBinaryOperator>(BO)) {
269 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
270 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
282 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
283 /// replaced with RepOp.
284 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
285 const TargetData *TD) {
286 // Trivial replacement.
290 Instruction *I = dyn_cast<Instruction>(V);
294 // If this is a binary operator, try to simplify it with the replaced op.
295 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
296 if (B->getOperand(0) == Op)
297 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD);
298 if (B->getOperand(1) == Op)
299 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD);
302 // Same for CmpInsts.
303 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
304 if (C->getOperand(0) == Op)
305 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD);
306 if (C->getOperand(1) == Op)
307 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD);
310 // TODO: We could hand off more cases to instsimplify here.
312 // If all operands are constant after substituting Op for RepOp then we can
313 // constant fold the instruction.
314 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
315 // Build a list of all constant operands.
316 SmallVector<Constant*, 8> ConstOps;
317 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
318 if (I->getOperand(i) == Op)
319 ConstOps.push_back(CRepOp);
320 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
321 ConstOps.push_back(COp);
326 // All operands were constants, fold it.
327 if (ConstOps.size() == I->getNumOperands())
328 return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
335 /// visitSelectInstWithICmp - Visit a SelectInst that has an
336 /// ICmpInst as its first operand.
338 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
340 bool Changed = false;
341 ICmpInst::Predicate Pred = ICI->getPredicate();
342 Value *CmpLHS = ICI->getOperand(0);
343 Value *CmpRHS = ICI->getOperand(1);
344 Value *TrueVal = SI.getTrueValue();
345 Value *FalseVal = SI.getFalseValue();
347 // Check cases where the comparison is with a constant that
348 // can be adjusted to fit the min/max idiom. We may move or edit ICI
349 // here, so make sure the select is the only user.
350 if (ICI->hasOneUse())
351 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
352 // X < MIN ? T : F --> F
353 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
354 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
355 return ReplaceInstUsesWith(SI, FalseVal);
356 // X > MAX ? T : F --> F
357 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
358 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
359 return ReplaceInstUsesWith(SI, FalseVal);
362 case ICmpInst::ICMP_ULT:
363 case ICmpInst::ICMP_SLT:
364 case ICmpInst::ICMP_UGT:
365 case ICmpInst::ICMP_SGT: {
366 // These transformations only work for selects over integers.
367 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
371 Constant *AdjustedRHS;
372 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
373 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
374 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
375 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
377 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
378 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
379 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
380 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
381 ; // Nothing to do here. Values match without any sign/zero extension.
383 // Types do not match. Instead of calculating this with mixed types
384 // promote all to the larger type. This enables scalar evolution to
385 // analyze this expression.
386 else if (CmpRHS->getType()->getScalarSizeInBits()
387 < SelectTy->getBitWidth()) {
388 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
390 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
391 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
392 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
393 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
394 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
395 sextRHS == FalseVal) {
397 AdjustedRHS = sextRHS;
398 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
399 sextRHS == TrueVal) {
401 AdjustedRHS = sextRHS;
402 } else if (ICI->isUnsigned()) {
403 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
404 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
405 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
406 // zext + signed compare cannot be changed:
407 // 0xff <s 0x00, but 0x00ff >s 0x0000
408 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
409 zextRHS == FalseVal) {
411 AdjustedRHS = zextRHS;
412 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
413 zextRHS == TrueVal) {
415 AdjustedRHS = zextRHS;
423 Pred = ICmpInst::getSwappedPredicate(Pred);
424 CmpRHS = AdjustedRHS;
425 std::swap(FalseVal, TrueVal);
426 ICI->setPredicate(Pred);
427 ICI->setOperand(0, CmpLHS);
428 ICI->setOperand(1, CmpRHS);
429 SI.setOperand(1, TrueVal);
430 SI.setOperand(2, FalseVal);
432 // Move ICI instruction right before the select instruction. Otherwise
433 // the sext/zext value may be defined after the ICI instruction uses it.
434 ICI->moveBefore(&SI);
442 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
443 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
444 // FIXME: Type and constness constraints could be lifted, but we have to
445 // watch code size carefully. We should consider xor instead of
446 // sub/add when we decide to do that.
447 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
448 if (TrueVal->getType() == Ty) {
449 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
450 ConstantInt *C1 = NULL, *C2 = NULL;
451 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
452 C1 = dyn_cast<ConstantInt>(TrueVal);
453 C2 = dyn_cast<ConstantInt>(FalseVal);
454 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
455 C1 = dyn_cast<ConstantInt>(FalseVal);
456 C2 = dyn_cast<ConstantInt>(TrueVal);
459 // This shift results in either -1 or 0.
460 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
462 // Check if we can express the operation with a single or.
463 if (C2->isAllOnesValue())
464 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
466 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
467 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
473 // If we have an equality comparison then we know the value in one of the
474 // arms of the select. See if substituting this value into the arm and
475 // simplifying the result yields the same value as the other arm.
476 if (Pred == ICmpInst::ICMP_EQ) {
477 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal ||
478 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal)
479 return ReplaceInstUsesWith(SI, FalseVal);
480 } else if (Pred == ICmpInst::ICMP_NE) {
481 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal ||
482 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal)
483 return ReplaceInstUsesWith(SI, TrueVal);
486 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
488 if (isa<Constant>(CmpRHS)) {
489 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
490 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
491 SI.setOperand(1, CmpRHS);
493 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
494 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
495 SI.setOperand(2, CmpRHS);
500 return Changed ? &SI : 0;
504 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
505 /// PHI node (but the two may be in different blocks). See if the true/false
506 /// values (V) are live in all of the predecessor blocks of the PHI. For
507 /// example, cases like this cannot be mapped:
509 /// X = phi [ C1, BB1], [C2, BB2]
511 /// Z = select X, Y, 0
513 /// because Y is not live in BB1/BB2.
515 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
516 const SelectInst &SI) {
517 // If the value is a non-instruction value like a constant or argument, it
518 // can always be mapped.
519 const Instruction *I = dyn_cast<Instruction>(V);
520 if (I == 0) return true;
522 // If V is a PHI node defined in the same block as the condition PHI, we can
523 // map the arguments.
524 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
526 if (const PHINode *VP = dyn_cast<PHINode>(I))
527 if (VP->getParent() == CondPHI->getParent())
530 // Otherwise, if the PHI and select are defined in the same block and if V is
531 // defined in a different block, then we can transform it.
532 if (SI.getParent() == CondPHI->getParent() &&
533 I->getParent() != CondPHI->getParent())
536 // Otherwise we have a 'hard' case and we can't tell without doing more
537 // detailed dominator based analysis, punt.
541 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
542 /// SPF2(SPF1(A, B), C)
543 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
544 SelectPatternFlavor SPF1,
547 SelectPatternFlavor SPF2, Value *C) {
548 if (C == A || C == B) {
549 // MAX(MAX(A, B), B) -> MAX(A, B)
550 // MIN(MIN(a, b), a) -> MIN(a, b)
552 return ReplaceInstUsesWith(Outer, Inner);
554 // MAX(MIN(a, b), a) -> a
555 // MIN(MAX(a, b), a) -> a
556 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
557 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
558 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
559 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
560 return ReplaceInstUsesWith(Outer, C);
563 // TODO: MIN(MIN(A, 23), 97)
568 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
569 /// both be) and we have an icmp instruction with zero, and we have an 'and'
570 /// with the non-constant value and a power of two we can turn the select
571 /// into a shift on the result of the 'and'.
572 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
573 ConstantInt *FalseVal,
574 InstCombiner::BuilderTy *Builder) {
575 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
576 if (!IC || !IC->isEquality())
579 if (!match(IC->getOperand(1), m_Zero()))
583 Value *LHS = IC->getOperand(0);
584 if (LHS->getType() != SI.getType() ||
585 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
588 // If both select arms are non-zero see if we have a select of the form
589 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
590 // for 'x ? 2^n : 0' and fix the thing up at the end.
591 ConstantInt *Offset = 0;
592 if (!TrueVal->isZero() && !FalseVal->isZero()) {
593 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
595 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
600 // Adjust TrueVal and FalseVal to the offset.
601 TrueVal = ConstantInt::get(Builder->getContext(),
602 TrueVal->getValue() - Offset->getValue());
603 FalseVal = ConstantInt::get(Builder->getContext(),
604 FalseVal->getValue() - Offset->getValue());
607 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
608 if (!AndRHS->getValue().isPowerOf2() ||
609 (!TrueVal->getValue().isPowerOf2() &&
610 !FalseVal->getValue().isPowerOf2()))
613 // Determine which shift is needed to transform result of the 'and' into the
615 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
616 unsigned ValZeros = ValC->getValue().logBase2();
617 unsigned AndZeros = AndRHS->getValue().logBase2();
620 if (ValZeros > AndZeros)
621 V = Builder->CreateShl(V, ValZeros - AndZeros);
622 else if (ValZeros < AndZeros)
623 V = Builder->CreateLShr(V, AndZeros - ValZeros);
625 // Okay, now we know that everything is set up, we just don't know whether we
626 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
627 bool ShouldNotVal = !TrueVal->isZero();
628 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
630 V = Builder->CreateXor(V, ValC);
632 // Apply an offset if needed.
634 V = Builder->CreateAdd(V, Offset);
638 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
639 Value *CondVal = SI.getCondition();
640 Value *TrueVal = SI.getTrueValue();
641 Value *FalseVal = SI.getFalseValue();
643 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
644 return ReplaceInstUsesWith(SI, V);
646 if (SI.getType()->isIntegerTy(1)) {
647 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
648 if (C->getZExtValue()) {
649 // Change: A = select B, true, C --> A = or B, C
650 return BinaryOperator::CreateOr(CondVal, FalseVal);
652 // Change: A = select B, false, C --> A = and !B, C
653 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
654 return BinaryOperator::CreateAnd(NotCond, FalseVal);
655 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
656 if (C->getZExtValue() == false) {
657 // Change: A = select B, C, false --> A = and B, C
658 return BinaryOperator::CreateAnd(CondVal, TrueVal);
660 // Change: A = select B, C, true --> A = or !B, C
661 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
662 return BinaryOperator::CreateOr(NotCond, TrueVal);
665 // select a, b, a -> a&b
666 // select a, a, b -> a|b
667 if (CondVal == TrueVal)
668 return BinaryOperator::CreateOr(CondVal, FalseVal);
669 else if (CondVal == FalseVal)
670 return BinaryOperator::CreateAnd(CondVal, TrueVal);
673 // Selecting between two integer constants?
674 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
675 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
676 // select C, 1, 0 -> zext C to int
677 if (FalseValC->isZero() && TrueValC->getValue() == 1)
678 return new ZExtInst(CondVal, SI.getType());
680 // select C, -1, 0 -> sext C to int
681 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
682 return new SExtInst(CondVal, SI.getType());
684 // select C, 0, 1 -> zext !C to int
685 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
686 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
687 return new ZExtInst(NotCond, SI.getType());
690 // select C, 0, -1 -> sext !C to int
691 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
692 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
693 return new SExtInst(NotCond, SI.getType());
696 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
697 return ReplaceInstUsesWith(SI, V);
700 // See if we are selecting two values based on a comparison of the two values.
701 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
702 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
703 // Transform (X == Y) ? X : Y -> Y
704 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
705 // This is not safe in general for floating point:
706 // consider X== -0, Y== +0.
707 // It becomes safe if either operand is a nonzero constant.
708 ConstantFP *CFPt, *CFPf;
709 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
710 !CFPt->getValueAPF().isZero()) ||
711 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
712 !CFPf->getValueAPF().isZero()))
713 return ReplaceInstUsesWith(SI, FalseVal);
715 // Transform (X une Y) ? X : Y -> X
716 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
717 // This is not safe in general for floating point:
718 // consider X== -0, Y== +0.
719 // It becomes safe if either operand is a nonzero constant.
720 ConstantFP *CFPt, *CFPf;
721 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
722 !CFPt->getValueAPF().isZero()) ||
723 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
724 !CFPf->getValueAPF().isZero()))
725 return ReplaceInstUsesWith(SI, TrueVal);
727 // NOTE: if we wanted to, this is where to detect MIN/MAX
729 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
730 // Transform (X == Y) ? Y : X -> X
731 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
732 // This is not safe in general for floating point:
733 // consider X== -0, Y== +0.
734 // It becomes safe if either operand is a nonzero constant.
735 ConstantFP *CFPt, *CFPf;
736 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
737 !CFPt->getValueAPF().isZero()) ||
738 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
739 !CFPf->getValueAPF().isZero()))
740 return ReplaceInstUsesWith(SI, FalseVal);
742 // Transform (X une Y) ? Y : X -> Y
743 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
744 // This is not safe in general for floating point:
745 // consider X== -0, Y== +0.
746 // It becomes safe if either operand is a nonzero constant.
747 ConstantFP *CFPt, *CFPf;
748 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
749 !CFPt->getValueAPF().isZero()) ||
750 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
751 !CFPf->getValueAPF().isZero()))
752 return ReplaceInstUsesWith(SI, TrueVal);
754 // NOTE: if we wanted to, this is where to detect MIN/MAX
756 // NOTE: if we wanted to, this is where to detect ABS
759 // See if we are selecting two values based on a comparison of the two values.
760 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
761 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
764 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
765 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
766 if (TI->hasOneUse() && FI->hasOneUse()) {
767 Instruction *AddOp = 0, *SubOp = 0;
769 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
770 if (TI->getOpcode() == FI->getOpcode())
771 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
774 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
775 // even legal for FP.
776 if ((TI->getOpcode() == Instruction::Sub &&
777 FI->getOpcode() == Instruction::Add) ||
778 (TI->getOpcode() == Instruction::FSub &&
779 FI->getOpcode() == Instruction::FAdd)) {
780 AddOp = FI; SubOp = TI;
781 } else if ((FI->getOpcode() == Instruction::Sub &&
782 TI->getOpcode() == Instruction::Add) ||
783 (FI->getOpcode() == Instruction::FSub &&
784 TI->getOpcode() == Instruction::FAdd)) {
785 AddOp = TI; SubOp = FI;
789 Value *OtherAddOp = 0;
790 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
791 OtherAddOp = AddOp->getOperand(1);
792 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
793 OtherAddOp = AddOp->getOperand(0);
797 // So at this point we know we have (Y -> OtherAddOp):
798 // select C, (add X, Y), (sub X, Z)
799 Value *NegVal; // Compute -Z
800 if (SI.getType()->isFPOrFPVectorTy()) {
801 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
803 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
806 Value *NewTrueOp = OtherAddOp;
807 Value *NewFalseOp = NegVal;
809 std::swap(NewTrueOp, NewFalseOp);
811 Builder->CreateSelect(CondVal, NewTrueOp,
812 NewFalseOp, SI.getName() + ".p");
814 if (SI.getType()->isFPOrFPVectorTy())
815 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
817 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
822 // See if we can fold the select into one of our operands.
823 if (SI.getType()->isIntegerTy()) {
824 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
827 // MAX(MAX(a, b), a) -> MAX(a, b)
828 // MIN(MIN(a, b), a) -> MIN(a, b)
829 // MAX(MIN(a, b), a) -> a
830 // MIN(MAX(a, b), a) -> a
831 Value *LHS, *RHS, *LHS2, *RHS2;
832 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
833 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
834 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
837 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
838 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
845 // ABS(ABS(X)) -> ABS(X)
848 // See if we can fold the select into a phi node if the condition is a select.
849 if (isa<PHINode>(SI.getCondition()))
850 // The true/false values have to be live in the PHI predecessor's blocks.
851 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
852 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
853 if (Instruction *NV = FoldOpIntoPhi(SI))
856 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
857 if (TrueSI->getCondition() == CondVal) {
858 SI.setOperand(1, TrueSI->getTrueValue());
862 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
863 if (FalseSI->getCondition() == CondVal) {
864 SI.setOperand(2, FalseSI->getFalseValue());
869 if (BinaryOperator::isNot(CondVal)) {
870 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
871 SI.setOperand(1, FalseVal);
872 SI.setOperand(2, TrueVal);