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/Analysis/ConstantFolding.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/Support/PatternMatch.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 Type *FIOpndTy = FI->getOperand(0)->getType();
131 if (TI->getOperand(0)->getType() != FIOpndTy)
133 // The select condition may be a vector. We may only change the operand
134 // type if the vector width remains the same (and matches the condition).
135 Type *CondTy = SI.getCondition()->getType();
136 if (CondTy->isVectorTy() && (!FIOpndTy->isVectorTy() ||
137 CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()))
140 return 0; // unknown unary op.
143 // Fold this by inserting a select from the input values.
144 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
145 FI->getOperand(0), SI.getName()+".v");
146 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
150 // Only handle binary operators here.
151 if (!isa<BinaryOperator>(TI))
154 // Figure out if the operations have any operands in common.
155 Value *MatchOp, *OtherOpT, *OtherOpF;
157 if (TI->getOperand(0) == FI->getOperand(0)) {
158 MatchOp = TI->getOperand(0);
159 OtherOpT = TI->getOperand(1);
160 OtherOpF = FI->getOperand(1);
161 MatchIsOpZero = true;
162 } else if (TI->getOperand(1) == FI->getOperand(1)) {
163 MatchOp = TI->getOperand(1);
164 OtherOpT = TI->getOperand(0);
165 OtherOpF = FI->getOperand(0);
166 MatchIsOpZero = false;
167 } else if (!TI->isCommutative()) {
169 } else if (TI->getOperand(0) == FI->getOperand(1)) {
170 MatchOp = TI->getOperand(0);
171 OtherOpT = TI->getOperand(1);
172 OtherOpF = FI->getOperand(0);
173 MatchIsOpZero = true;
174 } else if (TI->getOperand(1) == FI->getOperand(0)) {
175 MatchOp = TI->getOperand(1);
176 OtherOpT = TI->getOperand(0);
177 OtherOpF = FI->getOperand(1);
178 MatchIsOpZero = true;
183 // If we reach here, they do have operations in common.
184 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
185 OtherOpF, SI.getName()+".v");
187 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
189 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
191 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
193 llvm_unreachable("Shouldn't get here");
196 static bool isSelect01(Constant *C1, Constant *C2) {
197 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
200 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
203 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
205 return C1I->isOne() || C1I->isAllOnesValue() ||
206 C2I->isOne() || C2I->isAllOnesValue();
209 /// FoldSelectIntoOp - Try fold the select into one of the operands to
210 /// facilitate further optimization.
211 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
213 // See the comment above GetSelectFoldableOperands for a description of the
214 // transformation we are doing here.
215 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
216 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
217 !isa<Constant>(FalseVal)) {
218 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
219 unsigned OpToFold = 0;
220 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
222 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
227 Constant *C = GetSelectFoldableConstant(TVI);
228 Value *OOp = TVI->getOperand(2-OpToFold);
229 // Avoid creating select between 2 constants unless it's selecting
230 // between 0, 1 and -1.
231 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
232 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
233 NewSel->takeName(TVI);
234 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
235 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
237 if (isa<PossiblyExactOperator>(BO))
238 BO->setIsExact(TVI_BO->isExact());
239 if (isa<OverflowingBinaryOperator>(BO)) {
240 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
241 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
250 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
251 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
252 !isa<Constant>(TrueVal)) {
253 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
254 unsigned OpToFold = 0;
255 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
257 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
262 Constant *C = GetSelectFoldableConstant(FVI);
263 Value *OOp = FVI->getOperand(2-OpToFold);
264 // Avoid creating select between 2 constants unless it's selecting
265 // between 0, 1 and -1.
266 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
267 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
268 NewSel->takeName(FVI);
269 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
270 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
272 if (isa<PossiblyExactOperator>(BO))
273 BO->setIsExact(FVI_BO->isExact());
274 if (isa<OverflowingBinaryOperator>(BO)) {
275 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
276 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
288 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
289 /// replaced with RepOp.
290 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
291 const DataLayout *TD,
292 const TargetLibraryInfo *TLI) {
293 // Trivial replacement.
297 Instruction *I = dyn_cast<Instruction>(V);
301 // If this is a binary operator, try to simplify it with the replaced op.
302 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
303 if (B->getOperand(0) == Op)
304 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
305 if (B->getOperand(1) == Op)
306 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
309 // Same for CmpInsts.
310 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
311 if (C->getOperand(0) == Op)
312 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
314 if (C->getOperand(1) == Op)
315 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
319 // TODO: We could hand off more cases to instsimplify here.
321 // If all operands are constant after substituting Op for RepOp then we can
322 // constant fold the instruction.
323 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
324 // Build a list of all constant operands.
325 SmallVector<Constant*, 8> ConstOps;
326 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
327 if (I->getOperand(i) == Op)
328 ConstOps.push_back(CRepOp);
329 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
330 ConstOps.push_back(COp);
335 // All operands were constants, fold it.
336 if (ConstOps.size() == I->getNumOperands()) {
337 if (CmpInst *C = dyn_cast<CmpInst>(I))
338 return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
339 ConstOps[1], TD, TLI);
341 if (LoadInst *LI = dyn_cast<LoadInst>(I))
342 if (!LI->isVolatile())
343 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
345 return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
353 /// visitSelectInstWithICmp - Visit a SelectInst that has an
354 /// ICmpInst as its first operand.
356 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
358 bool Changed = false;
359 ICmpInst::Predicate Pred = ICI->getPredicate();
360 Value *CmpLHS = ICI->getOperand(0);
361 Value *CmpRHS = ICI->getOperand(1);
362 Value *TrueVal = SI.getTrueValue();
363 Value *FalseVal = SI.getFalseValue();
365 // Check cases where the comparison is with a constant that
366 // can be adjusted to fit the min/max idiom. We may move or edit ICI
367 // here, so make sure the select is the only user.
368 if (ICI->hasOneUse())
369 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
370 // X < MIN ? T : F --> F
371 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
372 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
373 return ReplaceInstUsesWith(SI, FalseVal);
374 // X > MAX ? T : F --> F
375 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
376 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
377 return ReplaceInstUsesWith(SI, FalseVal);
380 case ICmpInst::ICMP_ULT:
381 case ICmpInst::ICMP_SLT:
382 case ICmpInst::ICMP_UGT:
383 case ICmpInst::ICMP_SGT: {
384 // These transformations only work for selects over integers.
385 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
389 Constant *AdjustedRHS;
390 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
391 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
392 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
393 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
395 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
396 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
397 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
398 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
399 ; // Nothing to do here. Values match without any sign/zero extension.
401 // Types do not match. Instead of calculating this with mixed types
402 // promote all to the larger type. This enables scalar evolution to
403 // analyze this expression.
404 else if (CmpRHS->getType()->getScalarSizeInBits()
405 < SelectTy->getBitWidth()) {
406 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
408 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
409 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
410 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
411 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
412 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
413 sextRHS == FalseVal) {
415 AdjustedRHS = sextRHS;
416 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
417 sextRHS == TrueVal) {
419 AdjustedRHS = sextRHS;
420 } else if (ICI->isUnsigned()) {
421 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
422 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
423 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
424 // zext + signed compare cannot be changed:
425 // 0xff <s 0x00, but 0x00ff >s 0x0000
426 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
427 zextRHS == FalseVal) {
429 AdjustedRHS = zextRHS;
430 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
431 zextRHS == TrueVal) {
433 AdjustedRHS = zextRHS;
441 Pred = ICmpInst::getSwappedPredicate(Pred);
442 CmpRHS = AdjustedRHS;
443 std::swap(FalseVal, TrueVal);
444 ICI->setPredicate(Pred);
445 ICI->setOperand(0, CmpLHS);
446 ICI->setOperand(1, CmpRHS);
447 SI.setOperand(1, TrueVal);
448 SI.setOperand(2, FalseVal);
450 // Move ICI instruction right before the select instruction. Otherwise
451 // the sext/zext value may be defined after the ICI instruction uses it.
452 ICI->moveBefore(&SI);
460 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
461 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
462 // FIXME: Type and constness constraints could be lifted, but we have to
463 // watch code size carefully. We should consider xor instead of
464 // sub/add when we decide to do that.
465 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
466 if (TrueVal->getType() == Ty) {
467 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
468 ConstantInt *C1 = NULL, *C2 = NULL;
469 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
470 C1 = dyn_cast<ConstantInt>(TrueVal);
471 C2 = dyn_cast<ConstantInt>(FalseVal);
472 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
473 C1 = dyn_cast<ConstantInt>(FalseVal);
474 C2 = dyn_cast<ConstantInt>(TrueVal);
477 // This shift results in either -1 or 0.
478 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
480 // Check if we can express the operation with a single or.
481 if (C2->isAllOnesValue())
482 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
484 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
485 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
491 // If we have an equality comparison then we know the value in one of the
492 // arms of the select. See if substituting this value into the arm and
493 // simplifying the result yields the same value as the other arm.
494 if (Pred == ICmpInst::ICMP_EQ) {
495 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
496 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
497 return ReplaceInstUsesWith(SI, FalseVal);
498 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
499 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
500 return ReplaceInstUsesWith(SI, FalseVal);
501 } else if (Pred == ICmpInst::ICMP_NE) {
502 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
503 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
504 return ReplaceInstUsesWith(SI, TrueVal);
505 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
506 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
507 return ReplaceInstUsesWith(SI, TrueVal);
510 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
512 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
513 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
514 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
515 SI.setOperand(1, CmpRHS);
517 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
518 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
519 SI.setOperand(2, CmpRHS);
524 return Changed ? &SI : 0;
528 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
529 /// PHI node (but the two may be in different blocks). See if the true/false
530 /// values (V) are live in all of the predecessor blocks of the PHI. For
531 /// example, cases like this cannot be mapped:
533 /// X = phi [ C1, BB1], [C2, BB2]
535 /// Z = select X, Y, 0
537 /// because Y is not live in BB1/BB2.
539 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
540 const SelectInst &SI) {
541 // If the value is a non-instruction value like a constant or argument, it
542 // can always be mapped.
543 const Instruction *I = dyn_cast<Instruction>(V);
544 if (I == 0) return true;
546 // If V is a PHI node defined in the same block as the condition PHI, we can
547 // map the arguments.
548 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
550 if (const PHINode *VP = dyn_cast<PHINode>(I))
551 if (VP->getParent() == CondPHI->getParent())
554 // Otherwise, if the PHI and select are defined in the same block and if V is
555 // defined in a different block, then we can transform it.
556 if (SI.getParent() == CondPHI->getParent() &&
557 I->getParent() != CondPHI->getParent())
560 // Otherwise we have a 'hard' case and we can't tell without doing more
561 // detailed dominator based analysis, punt.
565 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
566 /// SPF2(SPF1(A, B), C)
567 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
568 SelectPatternFlavor SPF1,
571 SelectPatternFlavor SPF2, Value *C) {
572 if (C == A || C == B) {
573 // MAX(MAX(A, B), B) -> MAX(A, B)
574 // MIN(MIN(a, b), a) -> MIN(a, b)
576 return ReplaceInstUsesWith(Outer, Inner);
578 // MAX(MIN(a, b), a) -> a
579 // MIN(MAX(a, b), a) -> a
580 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
581 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
582 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
583 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
584 return ReplaceInstUsesWith(Outer, C);
587 // TODO: MIN(MIN(A, 23), 97)
592 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
593 /// both be) and we have an icmp instruction with zero, and we have an 'and'
594 /// with the non-constant value and a power of two we can turn the select
595 /// into a shift on the result of the 'and'.
596 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
597 ConstantInt *FalseVal,
598 InstCombiner::BuilderTy *Builder) {
599 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
600 if (!IC || !IC->isEquality())
603 if (!match(IC->getOperand(1), m_Zero()))
607 Value *LHS = IC->getOperand(0);
608 if (LHS->getType() != SI.getType() ||
609 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
612 // If both select arms are non-zero see if we have a select of the form
613 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
614 // for 'x ? 2^n : 0' and fix the thing up at the end.
615 ConstantInt *Offset = 0;
616 if (!TrueVal->isZero() && !FalseVal->isZero()) {
617 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
619 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
624 // Adjust TrueVal and FalseVal to the offset.
625 TrueVal = ConstantInt::get(Builder->getContext(),
626 TrueVal->getValue() - Offset->getValue());
627 FalseVal = ConstantInt::get(Builder->getContext(),
628 FalseVal->getValue() - Offset->getValue());
631 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
632 if (!AndRHS->getValue().isPowerOf2() ||
633 (!TrueVal->getValue().isPowerOf2() &&
634 !FalseVal->getValue().isPowerOf2()))
637 // Determine which shift is needed to transform result of the 'and' into the
639 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
640 unsigned ValZeros = ValC->getValue().logBase2();
641 unsigned AndZeros = AndRHS->getValue().logBase2();
644 if (ValZeros > AndZeros)
645 V = Builder->CreateShl(V, ValZeros - AndZeros);
646 else if (ValZeros < AndZeros)
647 V = Builder->CreateLShr(V, AndZeros - ValZeros);
649 // Okay, now we know that everything is set up, we just don't know whether we
650 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
651 bool ShouldNotVal = !TrueVal->isZero();
652 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
654 V = Builder->CreateXor(V, ValC);
656 // Apply an offset if needed.
658 V = Builder->CreateAdd(V, Offset);
662 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
663 Value *CondVal = SI.getCondition();
664 Value *TrueVal = SI.getTrueValue();
665 Value *FalseVal = SI.getFalseValue();
667 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
668 return ReplaceInstUsesWith(SI, V);
670 if (SI.getType()->isIntegerTy(1)) {
671 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
672 if (C->getZExtValue()) {
673 // Change: A = select B, true, C --> A = or B, C
674 return BinaryOperator::CreateOr(CondVal, FalseVal);
676 // Change: A = select B, false, C --> A = and !B, C
677 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
678 return BinaryOperator::CreateAnd(NotCond, FalseVal);
679 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
680 if (C->getZExtValue() == false) {
681 // Change: A = select B, C, false --> A = and B, C
682 return BinaryOperator::CreateAnd(CondVal, TrueVal);
684 // Change: A = select B, C, true --> A = or !B, C
685 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
686 return BinaryOperator::CreateOr(NotCond, TrueVal);
689 // select a, b, a -> a&b
690 // select a, a, b -> a|b
691 if (CondVal == TrueVal)
692 return BinaryOperator::CreateOr(CondVal, FalseVal);
693 else if (CondVal == FalseVal)
694 return BinaryOperator::CreateAnd(CondVal, TrueVal);
696 // select a, ~a, b -> (~a)&b
697 // select a, b, ~a -> (~a)|b
698 if (match(TrueVal, m_Not(m_Specific(CondVal))))
699 return BinaryOperator::CreateAnd(TrueVal, FalseVal);
700 else if (match(FalseVal, m_Not(m_Specific(CondVal))))
701 return BinaryOperator::CreateOr(TrueVal, FalseVal);
704 // Selecting between two integer constants?
705 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
706 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
707 // select C, 1, 0 -> zext C to int
708 if (FalseValC->isZero() && TrueValC->getValue() == 1)
709 return new ZExtInst(CondVal, SI.getType());
711 // select C, -1, 0 -> sext C to int
712 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
713 return new SExtInst(CondVal, SI.getType());
715 // select C, 0, 1 -> zext !C to int
716 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
717 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
718 return new ZExtInst(NotCond, SI.getType());
721 // select C, 0, -1 -> sext !C to int
722 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
723 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
724 return new SExtInst(NotCond, SI.getType());
727 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
728 return ReplaceInstUsesWith(SI, V);
731 // See if we are selecting two values based on a comparison of the two values.
732 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
733 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
734 // Transform (X == Y) ? X : Y -> Y
735 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
736 // This is not safe in general for floating point:
737 // consider X== -0, Y== +0.
738 // It becomes safe if either operand is a nonzero constant.
739 ConstantFP *CFPt, *CFPf;
740 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
741 !CFPt->getValueAPF().isZero()) ||
742 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
743 !CFPf->getValueAPF().isZero()))
744 return ReplaceInstUsesWith(SI, FalseVal);
746 // Transform (X une Y) ? X : Y -> X
747 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
748 // This is not safe in general for floating point:
749 // consider X== -0, Y== +0.
750 // It becomes safe if either operand is a nonzero constant.
751 ConstantFP *CFPt, *CFPf;
752 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
753 !CFPt->getValueAPF().isZero()) ||
754 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
755 !CFPf->getValueAPF().isZero()))
756 return ReplaceInstUsesWith(SI, TrueVal);
758 // NOTE: if we wanted to, this is where to detect MIN/MAX
760 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
761 // Transform (X == Y) ? Y : X -> X
762 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
763 // This is not safe in general for floating point:
764 // consider X== -0, Y== +0.
765 // It becomes safe if either operand is a nonzero constant.
766 ConstantFP *CFPt, *CFPf;
767 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
768 !CFPt->getValueAPF().isZero()) ||
769 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
770 !CFPf->getValueAPF().isZero()))
771 return ReplaceInstUsesWith(SI, FalseVal);
773 // Transform (X une Y) ? Y : X -> Y
774 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
775 // This is not safe in general for floating point:
776 // consider X== -0, Y== +0.
777 // It becomes safe if either operand is a nonzero constant.
778 ConstantFP *CFPt, *CFPf;
779 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
780 !CFPt->getValueAPF().isZero()) ||
781 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
782 !CFPf->getValueAPF().isZero()))
783 return ReplaceInstUsesWith(SI, TrueVal);
785 // NOTE: if we wanted to, this is where to detect MIN/MAX
787 // NOTE: if we wanted to, this is where to detect ABS
790 // See if we are selecting two values based on a comparison of the two values.
791 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
792 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
795 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
796 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
797 if (TI->hasOneUse() && FI->hasOneUse()) {
798 Instruction *AddOp = 0, *SubOp = 0;
800 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
801 if (TI->getOpcode() == FI->getOpcode())
802 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
805 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
806 // even legal for FP.
807 if ((TI->getOpcode() == Instruction::Sub &&
808 FI->getOpcode() == Instruction::Add) ||
809 (TI->getOpcode() == Instruction::FSub &&
810 FI->getOpcode() == Instruction::FAdd)) {
811 AddOp = FI; SubOp = TI;
812 } else if ((FI->getOpcode() == Instruction::Sub &&
813 TI->getOpcode() == Instruction::Add) ||
814 (FI->getOpcode() == Instruction::FSub &&
815 TI->getOpcode() == Instruction::FAdd)) {
816 AddOp = TI; SubOp = FI;
820 Value *OtherAddOp = 0;
821 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
822 OtherAddOp = AddOp->getOperand(1);
823 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
824 OtherAddOp = AddOp->getOperand(0);
828 // So at this point we know we have (Y -> OtherAddOp):
829 // select C, (add X, Y), (sub X, Z)
830 Value *NegVal; // Compute -Z
831 if (SI.getType()->isFPOrFPVectorTy()) {
832 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
834 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
837 Value *NewTrueOp = OtherAddOp;
838 Value *NewFalseOp = NegVal;
840 std::swap(NewTrueOp, NewFalseOp);
842 Builder->CreateSelect(CondVal, NewTrueOp,
843 NewFalseOp, SI.getName() + ".p");
845 if (SI.getType()->isFPOrFPVectorTy())
846 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
848 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
853 // See if we can fold the select into one of our operands.
854 if (SI.getType()->isIntegerTy()) {
855 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
858 // MAX(MAX(a, b), a) -> MAX(a, b)
859 // MIN(MIN(a, b), a) -> MIN(a, b)
860 // MAX(MIN(a, b), a) -> a
861 // MIN(MAX(a, b), a) -> a
862 Value *LHS, *RHS, *LHS2, *RHS2;
863 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
864 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
865 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
868 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
869 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
876 // ABS(ABS(X)) -> ABS(X)
879 // See if we can fold the select into a phi node if the condition is a select.
880 if (isa<PHINode>(SI.getCondition()))
881 // The true/false values have to be live in the PHI predecessor's blocks.
882 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
883 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
884 if (Instruction *NV = FoldOpIntoPhi(SI))
887 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
888 if (TrueSI->getCondition() == CondVal) {
889 if (SI.getTrueValue() == TrueSI->getTrueValue())
891 SI.setOperand(1, TrueSI->getTrueValue());
895 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
896 if (FalseSI->getCondition() == CondVal) {
897 if (SI.getFalseValue() == FalseSI->getFalseValue())
899 SI.setOperand(2, FalseSI->getFalseValue());
904 if (BinaryOperator::isNot(CondVal)) {
905 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
906 SI.setOperand(1, FalseVal);
907 SI.setOperand(2, TrueVal);
911 if (VectorType *VecTy = dyn_cast<VectorType>(SI.getType())) {
912 unsigned VWidth = VecTy->getNumElements();
913 APInt UndefElts(VWidth, 0);
914 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
915 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
917 return ReplaceInstUsesWith(SI, V);
921 if (ConstantVector *CV = dyn_cast<ConstantVector>(CondVal)) {
922 // Form a shufflevector instruction.
923 SmallVector<Constant *, 8> Mask(VWidth);
924 Type *Int32Ty = Type::getInt32Ty(CV->getContext());
925 for (unsigned i = 0; i != VWidth; ++i) {
926 Constant *Elem = cast<Constant>(CV->getOperand(i));
927 if (ConstantInt *E = dyn_cast<ConstantInt>(Elem))
928 Mask[i] = ConstantInt::get(Int32Ty, i + (E->isZero() ? VWidth : 0));
929 else if (isa<UndefValue>(Elem))
930 Mask[i] = UndefValue::get(Int32Ty);
934 Constant *MaskVal = ConstantVector::get(Mask);
935 Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
936 return ReplaceInstUsesWith(SI, V);
939 if (isa<ConstantAggregateZero>(CondVal)) {
940 return ReplaceInstUsesWith(SI, FalseVal);