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 "InstCombineInternal.h"
15 #include "llvm/Analysis/ConstantFolding.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/IR/PatternMatch.h"
19 using namespace PatternMatch;
21 #define DEBUG_TYPE "instcombine"
23 static SelectPatternFlavor
24 getInverseMinMaxSelectPattern(SelectPatternFlavor SPF) {
27 llvm_unreachable("unhandled!");
40 static CmpInst::Predicate getICmpPredicateForMinMax(SelectPatternFlavor SPF) {
43 llvm_unreachable("unhandled!");
46 return ICmpInst::ICMP_SLT;
48 return ICmpInst::ICMP_ULT;
50 return ICmpInst::ICMP_SGT;
52 return ICmpInst::ICMP_UGT;
56 static Value *generateMinMaxSelectPattern(InstCombiner::BuilderTy *Builder,
57 SelectPatternFlavor SPF, Value *A,
59 CmpInst::Predicate Pred = getICmpPredicateForMinMax(SPF);
60 return Builder->CreateSelect(Builder->CreateICmp(Pred, A, B), A, B);
63 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
64 /// returning the kind and providing the out parameter results if we
65 /// successfully match.
66 static SelectPatternFlavor
67 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
68 SelectInst *SI = dyn_cast<SelectInst>(V);
69 if (!SI) return SPF_UNKNOWN;
71 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
72 if (!ICI) return SPF_UNKNOWN;
74 ICmpInst::Predicate Pred = ICI->getPredicate();
75 Value *CmpLHS = ICI->getOperand(0);
76 Value *CmpRHS = ICI->getOperand(1);
77 Value *TrueVal = SI->getTrueValue();
78 Value *FalseVal = SI->getFalseValue();
83 // (icmp X, Y) ? X : Y
84 if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
86 default: return SPF_UNKNOWN; // Equality.
87 case ICmpInst::ICMP_UGT:
88 case ICmpInst::ICMP_UGE: return SPF_UMAX;
89 case ICmpInst::ICMP_SGT:
90 case ICmpInst::ICMP_SGE: return SPF_SMAX;
91 case ICmpInst::ICMP_ULT:
92 case ICmpInst::ICMP_ULE: return SPF_UMIN;
93 case ICmpInst::ICMP_SLT:
94 case ICmpInst::ICMP_SLE: return SPF_SMIN;
98 // (icmp X, Y) ? Y : X
99 if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
101 default: return SPF_UNKNOWN; // Equality.
102 case ICmpInst::ICMP_UGT:
103 case ICmpInst::ICMP_UGE: return SPF_UMIN;
104 case ICmpInst::ICMP_SGT:
105 case ICmpInst::ICMP_SGE: return SPF_SMIN;
106 case ICmpInst::ICMP_ULT:
107 case ICmpInst::ICMP_ULE: return SPF_UMAX;
108 case ICmpInst::ICMP_SLT:
109 case ICmpInst::ICMP_SLE: return SPF_SMAX;
113 if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
114 if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
115 (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
117 // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
118 // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
119 if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
120 return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
123 // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
124 // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
125 if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
126 return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
130 // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)
131 if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) {
132 if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() &&
133 (match(TrueVal, m_Not(m_Specific(CmpLHS))) ||
134 match(CmpLHS, m_Not(m_Specific(TrueVal))))) {
142 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
148 /// GetSelectFoldableOperands - We want to turn code that looks like this:
150 /// %D = select %cond, %C, %A
152 /// %C = select %cond, %B, 0
155 /// Assuming that the specified instruction is an operand to the select, return
156 /// a bitmask indicating which operands of this instruction are foldable if they
157 /// equal the other incoming value of the select.
159 static unsigned GetSelectFoldableOperands(Instruction *I) {
160 switch (I->getOpcode()) {
161 case Instruction::Add:
162 case Instruction::Mul:
163 case Instruction::And:
164 case Instruction::Or:
165 case Instruction::Xor:
166 return 3; // Can fold through either operand.
167 case Instruction::Sub: // Can only fold on the amount subtracted.
168 case Instruction::Shl: // Can only fold on the shift amount.
169 case Instruction::LShr:
170 case Instruction::AShr:
173 return 0; // Cannot fold
177 /// GetSelectFoldableConstant - For the same transformation as the previous
178 /// function, return the identity constant that goes into the select.
179 static Constant *GetSelectFoldableConstant(Instruction *I) {
180 switch (I->getOpcode()) {
181 default: llvm_unreachable("This cannot happen!");
182 case Instruction::Add:
183 case Instruction::Sub:
184 case Instruction::Or:
185 case Instruction::Xor:
186 case Instruction::Shl:
187 case Instruction::LShr:
188 case Instruction::AShr:
189 return Constant::getNullValue(I->getType());
190 case Instruction::And:
191 return Constant::getAllOnesValue(I->getType());
192 case Instruction::Mul:
193 return ConstantInt::get(I->getType(), 1);
197 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
198 /// have the same opcode and only one use each. Try to simplify this.
199 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
201 if (TI->getNumOperands() == 1) {
202 // If this is a non-volatile load or a cast from the same type,
205 Type *FIOpndTy = FI->getOperand(0)->getType();
206 if (TI->getOperand(0)->getType() != FIOpndTy)
208 // The select condition may be a vector. We may only change the operand
209 // type if the vector width remains the same (and matches the condition).
210 Type *CondTy = SI.getCondition()->getType();
211 if (CondTy->isVectorTy() && (!FIOpndTy->isVectorTy() ||
212 CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()))
215 return nullptr; // unknown unary op.
218 // Fold this by inserting a select from the input values.
219 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
220 FI->getOperand(0), SI.getName()+".v");
221 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
225 // Only handle binary operators here.
226 if (!isa<BinaryOperator>(TI))
229 // Figure out if the operations have any operands in common.
230 Value *MatchOp, *OtherOpT, *OtherOpF;
232 if (TI->getOperand(0) == FI->getOperand(0)) {
233 MatchOp = TI->getOperand(0);
234 OtherOpT = TI->getOperand(1);
235 OtherOpF = FI->getOperand(1);
236 MatchIsOpZero = true;
237 } else if (TI->getOperand(1) == FI->getOperand(1)) {
238 MatchOp = TI->getOperand(1);
239 OtherOpT = TI->getOperand(0);
240 OtherOpF = FI->getOperand(0);
241 MatchIsOpZero = false;
242 } else if (!TI->isCommutative()) {
244 } else if (TI->getOperand(0) == FI->getOperand(1)) {
245 MatchOp = TI->getOperand(0);
246 OtherOpT = TI->getOperand(1);
247 OtherOpF = FI->getOperand(0);
248 MatchIsOpZero = true;
249 } else if (TI->getOperand(1) == FI->getOperand(0)) {
250 MatchOp = TI->getOperand(1);
251 OtherOpT = TI->getOperand(0);
252 OtherOpF = FI->getOperand(1);
253 MatchIsOpZero = true;
258 // If we reach here, they do have operations in common.
259 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
260 OtherOpF, SI.getName()+".v");
262 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
264 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
266 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
268 llvm_unreachable("Shouldn't get here");
271 static bool isSelect01(Constant *C1, Constant *C2) {
272 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
275 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
278 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
280 return C1I->isOne() || C1I->isAllOnesValue() ||
281 C2I->isOne() || C2I->isAllOnesValue();
284 /// FoldSelectIntoOp - Try fold the select into one of the operands to
285 /// facilitate further optimization.
286 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
288 // See the comment above GetSelectFoldableOperands for a description of the
289 // transformation we are doing here.
290 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
291 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
292 !isa<Constant>(FalseVal)) {
293 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
294 unsigned OpToFold = 0;
295 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
297 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
302 Constant *C = GetSelectFoldableConstant(TVI);
303 Value *OOp = TVI->getOperand(2-OpToFold);
304 // Avoid creating select between 2 constants unless it's selecting
305 // between 0, 1 and -1.
306 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
307 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
308 NewSel->takeName(TVI);
309 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
310 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
312 if (isa<PossiblyExactOperator>(BO))
313 BO->setIsExact(TVI_BO->isExact());
314 if (isa<OverflowingBinaryOperator>(BO)) {
315 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
316 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
325 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
326 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
327 !isa<Constant>(TrueVal)) {
328 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
329 unsigned OpToFold = 0;
330 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
332 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
337 Constant *C = GetSelectFoldableConstant(FVI);
338 Value *OOp = FVI->getOperand(2-OpToFold);
339 // Avoid creating select between 2 constants unless it's selecting
340 // between 0, 1 and -1.
341 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
342 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
343 NewSel->takeName(FVI);
344 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
345 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
347 if (isa<PossiblyExactOperator>(BO))
348 BO->setIsExact(FVI_BO->isExact());
349 if (isa<OverflowingBinaryOperator>(BO)) {
350 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
351 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
363 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
364 /// replaced with RepOp.
365 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
366 const TargetLibraryInfo *TLI,
367 const DataLayout &DL, DominatorTree *DT,
368 AssumptionCache *AC) {
369 // Trivial replacement.
373 Instruction *I = dyn_cast<Instruction>(V);
377 // If this is a binary operator, try to simplify it with the replaced op.
378 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
379 if (B->getOperand(0) == Op)
380 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
381 if (B->getOperand(1) == Op)
382 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
385 // Same for CmpInsts.
386 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
387 if (C->getOperand(0) == Op)
388 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), DL,
390 if (C->getOperand(1) == Op)
391 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, DL,
395 // TODO: We could hand off more cases to instsimplify here.
397 // If all operands are constant after substituting Op for RepOp then we can
398 // constant fold the instruction.
399 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
400 // Build a list of all constant operands.
401 SmallVector<Constant*, 8> ConstOps;
402 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
403 if (I->getOperand(i) == Op)
404 ConstOps.push_back(CRepOp);
405 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
406 ConstOps.push_back(COp);
411 // All operands were constants, fold it.
412 if (ConstOps.size() == I->getNumOperands()) {
413 if (CmpInst *C = dyn_cast<CmpInst>(I))
414 return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
415 ConstOps[1], DL, TLI);
417 if (LoadInst *LI = dyn_cast<LoadInst>(I))
418 if (!LI->isVolatile())
419 return ConstantFoldLoadFromConstPtr(ConstOps[0], DL);
421 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), ConstOps,
429 /// foldSelectICmpAndOr - We want to turn:
430 /// (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
432 /// (or (shl (and X, C1), C3), y)
434 /// C1 and C2 are both powers of 2
436 /// C3 = Log(C2) - Log(C1)
438 /// This transform handles cases where:
439 /// 1. The icmp predicate is inverted
440 /// 2. The select operands are reversed
441 /// 3. The magnitude of C2 and C1 are flipped
442 static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
444 InstCombiner::BuilderTy *Builder) {
445 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
446 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
449 Value *CmpLHS = IC->getOperand(0);
450 Value *CmpRHS = IC->getOperand(1);
452 if (!match(CmpRHS, m_Zero()))
457 if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
461 bool OrOnTrueVal = false;
462 bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
464 OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
466 if (!OrOnFalseVal && !OrOnTrueVal)
470 Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
472 unsigned C1Log = C1->logBase2();
473 unsigned C2Log = C2->logBase2();
475 V = Builder->CreateZExtOrTrunc(V, Y->getType());
476 V = Builder->CreateShl(V, C2Log - C1Log);
477 } else if (C1Log > C2Log) {
478 V = Builder->CreateLShr(V, C1Log - C2Log);
479 V = Builder->CreateZExtOrTrunc(V, Y->getType());
481 V = Builder->CreateZExtOrTrunc(V, Y->getType());
483 ICmpInst::Predicate Pred = IC->getPredicate();
484 if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
485 (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
486 V = Builder->CreateXor(V, *C2);
488 return Builder->CreateOr(V, Y);
491 /// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
492 /// call to cttz/ctlz with flag 'is_zero_undef' cleared.
494 /// For example, we can fold the following code sequence:
496 /// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
497 /// %1 = icmp ne i32 %x, 0
498 /// %2 = select i1 %1, i32 %0, i32 32
502 /// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
503 static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
504 InstCombiner::BuilderTy *Builder) {
505 ICmpInst::Predicate Pred = ICI->getPredicate();
506 Value *CmpLHS = ICI->getOperand(0);
507 Value *CmpRHS = ICI->getOperand(1);
509 // Check if the condition value compares a value for equality against zero.
510 if (!ICI->isEquality() || !match(CmpRHS, m_Zero()))
513 Value *Count = FalseVal;
514 Value *ValueOnZero = TrueVal;
515 if (Pred == ICmpInst::ICMP_NE)
516 std::swap(Count, ValueOnZero);
518 // Skip zero extend/truncate.
520 if (match(Count, m_ZExt(m_Value(V))) ||
521 match(Count, m_Trunc(m_Value(V))))
524 // Check if the value propagated on zero is a constant number equal to the
525 // sizeof in bits of 'Count'.
526 unsigned SizeOfInBits = Count->getType()->getScalarSizeInBits();
527 if (!match(ValueOnZero, m_SpecificInt(SizeOfInBits)))
530 // Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the
531 // input to the cttz/ctlz is used as LHS for the compare instruction.
532 if (match(Count, m_Intrinsic<Intrinsic::cttz>(m_Specific(CmpLHS))) ||
533 match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS)))) {
534 IntrinsicInst *II = cast<IntrinsicInst>(Count);
535 IRBuilder<> Builder(II);
536 // Explicitly clear the 'undef_on_zero' flag.
537 IntrinsicInst *NewI = cast<IntrinsicInst>(II->clone());
538 Type *Ty = NewI->getArgOperand(1)->getType();
539 NewI->setArgOperand(1, Constant::getNullValue(Ty));
540 Builder.Insert(NewI);
541 return Builder.CreateZExtOrTrunc(NewI, ValueOnZero->getType());
547 /// visitSelectInstWithICmp - Visit a SelectInst that has an
548 /// ICmpInst as its first operand.
550 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
552 bool Changed = false;
553 ICmpInst::Predicate Pred = ICI->getPredicate();
554 Value *CmpLHS = ICI->getOperand(0);
555 Value *CmpRHS = ICI->getOperand(1);
556 Value *TrueVal = SI.getTrueValue();
557 Value *FalseVal = SI.getFalseValue();
559 // Check cases where the comparison is with a constant that
560 // can be adjusted to fit the min/max idiom. We may move or edit ICI
561 // here, so make sure the select is the only user.
562 if (ICI->hasOneUse())
563 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
564 // X < MIN ? T : F --> F
565 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
566 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
567 return ReplaceInstUsesWith(SI, FalseVal);
568 // X > MAX ? T : F --> F
569 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
570 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
571 return ReplaceInstUsesWith(SI, FalseVal);
574 case ICmpInst::ICMP_ULT:
575 case ICmpInst::ICMP_SLT:
576 case ICmpInst::ICMP_UGT:
577 case ICmpInst::ICMP_SGT: {
578 // These transformations only work for selects over integers.
579 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
583 Constant *AdjustedRHS;
584 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
585 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
586 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
587 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
589 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
590 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
591 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
592 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
593 ; // Nothing to do here. Values match without any sign/zero extension.
595 // Types do not match. Instead of calculating this with mixed types
596 // promote all to the larger type. This enables scalar evolution to
597 // analyze this expression.
598 else if (CmpRHS->getType()->getScalarSizeInBits()
599 < SelectTy->getBitWidth()) {
600 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
602 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
603 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
604 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
605 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
606 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
607 sextRHS == FalseVal) {
609 AdjustedRHS = sextRHS;
610 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
611 sextRHS == TrueVal) {
613 AdjustedRHS = sextRHS;
614 } else if (ICI->isUnsigned()) {
615 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
616 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
617 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
618 // zext + signed compare cannot be changed:
619 // 0xff <s 0x00, but 0x00ff >s 0x0000
620 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
621 zextRHS == FalseVal) {
623 AdjustedRHS = zextRHS;
624 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
625 zextRHS == TrueVal) {
627 AdjustedRHS = zextRHS;
635 Pred = ICmpInst::getSwappedPredicate(Pred);
636 CmpRHS = AdjustedRHS;
637 std::swap(FalseVal, TrueVal);
638 ICI->setPredicate(Pred);
639 ICI->setOperand(0, CmpLHS);
640 ICI->setOperand(1, CmpRHS);
641 SI.setOperand(1, TrueVal);
642 SI.setOperand(2, FalseVal);
644 // Move ICI instruction right before the select instruction. Otherwise
645 // the sext/zext value may be defined after the ICI instruction uses it.
646 ICI->moveBefore(&SI);
654 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
655 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
656 // FIXME: Type and constness constraints could be lifted, but we have to
657 // watch code size carefully. We should consider xor instead of
658 // sub/add when we decide to do that.
659 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
660 if (TrueVal->getType() == Ty) {
661 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
662 ConstantInt *C1 = nullptr, *C2 = nullptr;
663 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
664 C1 = dyn_cast<ConstantInt>(TrueVal);
665 C2 = dyn_cast<ConstantInt>(FalseVal);
666 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
667 C1 = dyn_cast<ConstantInt>(FalseVal);
668 C2 = dyn_cast<ConstantInt>(TrueVal);
671 // This shift results in either -1 or 0.
672 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
674 // Check if we can express the operation with a single or.
675 if (C2->isAllOnesValue())
676 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
678 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
679 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
685 // If we have an equality comparison then we know the value in one of the
686 // arms of the select. See if substituting this value into the arm and
687 // simplifying the result yields the same value as the other arm.
688 if (Pred == ICmpInst::ICMP_EQ) {
689 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
691 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
693 return ReplaceInstUsesWith(SI, FalseVal);
694 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
696 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
698 return ReplaceInstUsesWith(SI, FalseVal);
699 } else if (Pred == ICmpInst::ICMP_NE) {
700 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
702 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
704 return ReplaceInstUsesWith(SI, TrueVal);
705 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
707 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
709 return ReplaceInstUsesWith(SI, TrueVal);
712 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
714 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
715 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
716 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
717 SI.setOperand(1, CmpRHS);
719 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
720 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
721 SI.setOperand(2, CmpRHS);
726 if (unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits()) {
727 APInt MinSignedValue = APInt::getSignBit(BitWidth);
731 bool IsBitTest = false;
732 if (ICmpInst::isEquality(Pred) &&
733 match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
734 match(CmpRHS, m_Zero())) {
736 TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
737 } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
741 TrueWhenUnset = false;
742 } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
746 TrueWhenUnset = true;
750 // (X & Y) == 0 ? X : X ^ Y --> X & ~Y
751 if (TrueWhenUnset && TrueVal == X &&
752 match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
753 V = Builder->CreateAnd(X, ~(*Y));
754 // (X & Y) != 0 ? X ^ Y : X --> X & ~Y
755 else if (!TrueWhenUnset && FalseVal == X &&
756 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
757 V = Builder->CreateAnd(X, ~(*Y));
758 // (X & Y) == 0 ? X ^ Y : X --> X | Y
759 else if (TrueWhenUnset && FalseVal == X &&
760 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
761 V = Builder->CreateOr(X, *Y);
762 // (X & Y) != 0 ? X : X ^ Y --> X | Y
763 else if (!TrueWhenUnset && TrueVal == X &&
764 match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
765 V = Builder->CreateOr(X, *Y);
768 return ReplaceInstUsesWith(SI, V);
772 if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
773 return ReplaceInstUsesWith(SI, V);
775 if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder))
776 return ReplaceInstUsesWith(SI, V);
778 return Changed ? &SI : nullptr;
782 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
783 /// PHI node (but the two may be in different blocks). See if the true/false
784 /// values (V) are live in all of the predecessor blocks of the PHI. For
785 /// example, cases like this cannot be mapped:
787 /// X = phi [ C1, BB1], [C2, BB2]
789 /// Z = select X, Y, 0
791 /// because Y is not live in BB1/BB2.
793 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
794 const SelectInst &SI) {
795 // If the value is a non-instruction value like a constant or argument, it
796 // can always be mapped.
797 const Instruction *I = dyn_cast<Instruction>(V);
800 // If V is a PHI node defined in the same block as the condition PHI, we can
801 // map the arguments.
802 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
804 if (const PHINode *VP = dyn_cast<PHINode>(I))
805 if (VP->getParent() == CondPHI->getParent())
808 // Otherwise, if the PHI and select are defined in the same block and if V is
809 // defined in a different block, then we can transform it.
810 if (SI.getParent() == CondPHI->getParent() &&
811 I->getParent() != CondPHI->getParent())
814 // Otherwise we have a 'hard' case and we can't tell without doing more
815 // detailed dominator based analysis, punt.
819 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
820 /// SPF2(SPF1(A, B), C)
821 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
822 SelectPatternFlavor SPF1,
825 SelectPatternFlavor SPF2, Value *C) {
826 if (C == A || C == B) {
827 // MAX(MAX(A, B), B) -> MAX(A, B)
828 // MIN(MIN(a, b), a) -> MIN(a, b)
830 return ReplaceInstUsesWith(Outer, Inner);
832 // MAX(MIN(a, b), a) -> a
833 // MIN(MAX(a, b), a) -> a
834 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
835 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
836 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
837 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
838 return ReplaceInstUsesWith(Outer, C);
842 if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
843 if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
844 APInt ACB = CB->getValue();
845 APInt ACC = CC->getValue();
847 // MIN(MIN(A, 23), 97) -> MIN(A, 23)
848 // MAX(MAX(A, 97), 23) -> MAX(A, 97)
849 if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
850 (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
851 (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
852 (SPF1 == SPF_SMAX && ACB.sge(ACC)))
853 return ReplaceInstUsesWith(Outer, Inner);
855 // MIN(MIN(A, 97), 23) -> MIN(A, 23)
856 // MAX(MAX(A, 23), 97) -> MAX(A, 97)
857 if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
858 (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
859 (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
860 (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
861 Outer.replaceUsesOfWith(Inner, A);
868 // ABS(ABS(X)) -> ABS(X)
869 // NABS(NABS(X)) -> NABS(X)
870 if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
871 return ReplaceInstUsesWith(Outer, Inner);
874 // ABS(NABS(X)) -> ABS(X)
875 // NABS(ABS(X)) -> NABS(X)
876 if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
877 (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
878 SelectInst *SI = cast<SelectInst>(Inner);
879 Value *NewSI = Builder->CreateSelect(
880 SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
881 return ReplaceInstUsesWith(Outer, NewSI);
884 auto IsFreeOrProfitableToInvert =
885 [&](Value *V, Value *&NotV, bool &ElidesXor) {
886 if (match(V, m_Not(m_Value(NotV)))) {
887 // If V has at most 2 uses then we can get rid of the xor operation
889 ElidesXor |= !V->hasNUsesOrMore(3);
893 if (IsFreeToInvert(V, !V->hasNUsesOrMore(3))) {
901 Value *NotA, *NotB, *NotC;
902 bool ElidesXor = false;
904 // MIN(MIN(~A, ~B), ~C) == ~MAX(MAX(A, B), C)
905 // MIN(MAX(~A, ~B), ~C) == ~MAX(MIN(A, B), C)
906 // MAX(MIN(~A, ~B), ~C) == ~MIN(MAX(A, B), C)
907 // MAX(MAX(~A, ~B), ~C) == ~MIN(MIN(A, B), C)
909 // This transform is performance neutral if we can elide at least one xor from
910 // the set of three operands, since we'll be tacking on an xor at the very
912 if (IsFreeOrProfitableToInvert(A, NotA, ElidesXor) &&
913 IsFreeOrProfitableToInvert(B, NotB, ElidesXor) &&
914 IsFreeOrProfitableToInvert(C, NotC, ElidesXor) && ElidesXor) {
916 NotA = Builder->CreateNot(A);
918 NotB = Builder->CreateNot(B);
920 NotC = Builder->CreateNot(C);
922 Value *NewInner = generateMinMaxSelectPattern(
923 Builder, getInverseMinMaxSelectPattern(SPF1), NotA, NotB);
924 Value *NewOuter = Builder->CreateNot(generateMinMaxSelectPattern(
925 Builder, getInverseMinMaxSelectPattern(SPF2), NewInner, NotC));
926 return ReplaceInstUsesWith(Outer, NewOuter);
932 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
933 /// both be) and we have an icmp instruction with zero, and we have an 'and'
934 /// with the non-constant value and a power of two we can turn the select
935 /// into a shift on the result of the 'and'.
936 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
937 ConstantInt *FalseVal,
938 InstCombiner::BuilderTy *Builder) {
939 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
940 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
943 if (!match(IC->getOperand(1), m_Zero()))
947 Value *LHS = IC->getOperand(0);
948 if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
951 // If both select arms are non-zero see if we have a select of the form
952 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
953 // for 'x ? 2^n : 0' and fix the thing up at the end.
954 ConstantInt *Offset = nullptr;
955 if (!TrueVal->isZero() && !FalseVal->isZero()) {
956 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
958 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
963 // Adjust TrueVal and FalseVal to the offset.
964 TrueVal = ConstantInt::get(Builder->getContext(),
965 TrueVal->getValue() - Offset->getValue());
966 FalseVal = ConstantInt::get(Builder->getContext(),
967 FalseVal->getValue() - Offset->getValue());
970 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
971 if (!AndRHS->getValue().isPowerOf2() ||
972 (!TrueVal->getValue().isPowerOf2() &&
973 !FalseVal->getValue().isPowerOf2()))
976 // Determine which shift is needed to transform result of the 'and' into the
978 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
979 unsigned ValZeros = ValC->getValue().logBase2();
980 unsigned AndZeros = AndRHS->getValue().logBase2();
982 // If types don't match we can still convert the select by introducing a zext
983 // or a trunc of the 'and'. The trunc case requires that all of the truncated
984 // bits are zero, we can figure that out by looking at the 'and' mask.
985 if (AndZeros >= ValC->getBitWidth())
988 Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
989 if (ValZeros > AndZeros)
990 V = Builder->CreateShl(V, ValZeros - AndZeros);
991 else if (ValZeros < AndZeros)
992 V = Builder->CreateLShr(V, AndZeros - ValZeros);
994 // Okay, now we know that everything is set up, we just don't know whether we
995 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
996 bool ShouldNotVal = !TrueVal->isZero();
997 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
999 V = Builder->CreateXor(V, ValC);
1001 // Apply an offset if needed.
1003 V = Builder->CreateAdd(V, Offset);
1007 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
1008 Value *CondVal = SI.getCondition();
1009 Value *TrueVal = SI.getTrueValue();
1010 Value *FalseVal = SI.getFalseValue();
1013 SimplifySelectInst(CondVal, TrueVal, FalseVal, DL, TLI, DT, AC))
1014 return ReplaceInstUsesWith(SI, V);
1016 if (SI.getType()->isIntegerTy(1)) {
1017 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
1018 if (C->getZExtValue()) {
1019 // Change: A = select B, true, C --> A = or B, C
1020 return BinaryOperator::CreateOr(CondVal, FalseVal);
1022 // Change: A = select B, false, C --> A = and !B, C
1023 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
1024 return BinaryOperator::CreateAnd(NotCond, FalseVal);
1026 if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
1027 if (!C->getZExtValue()) {
1028 // Change: A = select B, C, false --> A = and B, C
1029 return BinaryOperator::CreateAnd(CondVal, TrueVal);
1031 // Change: A = select B, C, true --> A = or !B, C
1032 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
1033 return BinaryOperator::CreateOr(NotCond, TrueVal);
1036 // select a, b, a -> a&b
1037 // select a, a, b -> a|b
1038 if (CondVal == TrueVal)
1039 return BinaryOperator::CreateOr(CondVal, FalseVal);
1040 if (CondVal == FalseVal)
1041 return BinaryOperator::CreateAnd(CondVal, TrueVal);
1043 // select a, ~a, b -> (~a)&b
1044 // select a, b, ~a -> (~a)|b
1045 if (match(TrueVal, m_Not(m_Specific(CondVal))))
1046 return BinaryOperator::CreateAnd(TrueVal, FalseVal);
1047 if (match(FalseVal, m_Not(m_Specific(CondVal))))
1048 return BinaryOperator::CreateOr(TrueVal, FalseVal);
1051 // Selecting between two integer constants?
1052 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
1053 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
1054 // select C, 1, 0 -> zext C to int
1055 if (FalseValC->isZero() && TrueValC->getValue() == 1)
1056 return new ZExtInst(CondVal, SI.getType());
1058 // select C, -1, 0 -> sext C to int
1059 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
1060 return new SExtInst(CondVal, SI.getType());
1062 // select C, 0, 1 -> zext !C to int
1063 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
1064 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
1065 return new ZExtInst(NotCond, SI.getType());
1068 // select C, 0, -1 -> sext !C to int
1069 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
1070 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
1071 return new SExtInst(NotCond, SI.getType());
1074 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
1075 return ReplaceInstUsesWith(SI, V);
1078 // See if we are selecting two values based on a comparison of the two values.
1079 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
1080 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
1081 // Transform (X == Y) ? X : Y -> Y
1082 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
1083 // This is not safe in general for floating point:
1084 // consider X== -0, Y== +0.
1085 // It becomes safe if either operand is a nonzero constant.
1086 ConstantFP *CFPt, *CFPf;
1087 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1088 !CFPt->getValueAPF().isZero()) ||
1089 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1090 !CFPf->getValueAPF().isZero()))
1091 return ReplaceInstUsesWith(SI, FalseVal);
1093 // Transform (X une Y) ? X : Y -> X
1094 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
1095 // This is not safe in general for floating point:
1096 // consider X== -0, Y== +0.
1097 // It becomes safe if either operand is a nonzero constant.
1098 ConstantFP *CFPt, *CFPf;
1099 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1100 !CFPt->getValueAPF().isZero()) ||
1101 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1102 !CFPf->getValueAPF().isZero()))
1103 return ReplaceInstUsesWith(SI, TrueVal);
1106 // Canonicalize to use ordered comparisons by swapping the select
1110 // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
1111 if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
1112 FCmpInst::Predicate InvPred = FCI->getInversePredicate();
1113 Value *NewCond = Builder->CreateFCmp(InvPred, TrueVal, FalseVal,
1114 FCI->getName() + ".inv");
1116 return SelectInst::Create(NewCond, FalseVal, TrueVal,
1117 SI.getName() + ".p");
1120 // NOTE: if we wanted to, this is where to detect MIN/MAX
1121 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
1122 // Transform (X == Y) ? Y : X -> X
1123 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
1124 // This is not safe in general for floating point:
1125 // consider X== -0, Y== +0.
1126 // It becomes safe if either operand is a nonzero constant.
1127 ConstantFP *CFPt, *CFPf;
1128 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1129 !CFPt->getValueAPF().isZero()) ||
1130 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1131 !CFPf->getValueAPF().isZero()))
1132 return ReplaceInstUsesWith(SI, FalseVal);
1134 // Transform (X une Y) ? Y : X -> Y
1135 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
1136 // This is not safe in general for floating point:
1137 // consider X== -0, Y== +0.
1138 // It becomes safe if either operand is a nonzero constant.
1139 ConstantFP *CFPt, *CFPf;
1140 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1141 !CFPt->getValueAPF().isZero()) ||
1142 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1143 !CFPf->getValueAPF().isZero()))
1144 return ReplaceInstUsesWith(SI, TrueVal);
1147 // Canonicalize to use ordered comparisons by swapping the select
1151 // (X ugt Y) ? X : Y -> (X ole Y) ? X : Y
1152 if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
1153 FCmpInst::Predicate InvPred = FCI->getInversePredicate();
1154 Value *NewCond = Builder->CreateFCmp(InvPred, FalseVal, TrueVal,
1155 FCI->getName() + ".inv");
1157 return SelectInst::Create(NewCond, FalseVal, TrueVal,
1158 SI.getName() + ".p");
1161 // NOTE: if we wanted to, this is where to detect MIN/MAX
1163 // NOTE: if we wanted to, this is where to detect ABS
1166 // See if we are selecting two values based on a comparison of the two values.
1167 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
1168 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
1171 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
1172 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
1173 if (TI->hasOneUse() && FI->hasOneUse()) {
1174 Instruction *AddOp = nullptr, *SubOp = nullptr;
1176 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
1177 if (TI->getOpcode() == FI->getOpcode())
1178 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
1181 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
1182 // even legal for FP.
1183 if ((TI->getOpcode() == Instruction::Sub &&
1184 FI->getOpcode() == Instruction::Add) ||
1185 (TI->getOpcode() == Instruction::FSub &&
1186 FI->getOpcode() == Instruction::FAdd)) {
1187 AddOp = FI; SubOp = TI;
1188 } else if ((FI->getOpcode() == Instruction::Sub &&
1189 TI->getOpcode() == Instruction::Add) ||
1190 (FI->getOpcode() == Instruction::FSub &&
1191 TI->getOpcode() == Instruction::FAdd)) {
1192 AddOp = TI; SubOp = FI;
1196 Value *OtherAddOp = nullptr;
1197 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
1198 OtherAddOp = AddOp->getOperand(1);
1199 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
1200 OtherAddOp = AddOp->getOperand(0);
1204 // So at this point we know we have (Y -> OtherAddOp):
1205 // select C, (add X, Y), (sub X, Z)
1206 Value *NegVal; // Compute -Z
1207 if (SI.getType()->isFPOrFPVectorTy()) {
1208 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
1209 if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
1210 FastMathFlags Flags = AddOp->getFastMathFlags();
1211 Flags &= SubOp->getFastMathFlags();
1212 NegInst->setFastMathFlags(Flags);
1215 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
1218 Value *NewTrueOp = OtherAddOp;
1219 Value *NewFalseOp = NegVal;
1221 std::swap(NewTrueOp, NewFalseOp);
1223 Builder->CreateSelect(CondVal, NewTrueOp,
1224 NewFalseOp, SI.getName() + ".p");
1226 if (SI.getType()->isFPOrFPVectorTy()) {
1228 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
1230 FastMathFlags Flags = AddOp->getFastMathFlags();
1231 Flags &= SubOp->getFastMathFlags();
1232 RI->setFastMathFlags(Flags);
1235 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
1240 // See if we can fold the select into one of our operands.
1241 if (SI.getType()->isIntegerTy()) {
1242 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
1245 Value *LHS, *RHS, *LHS2, *RHS2;
1246 SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS);
1248 // MAX(MAX(a, b), a) -> MAX(a, b)
1249 // MIN(MIN(a, b), a) -> MIN(a, b)
1250 // MAX(MIN(a, b), a) -> a
1251 // MIN(MAX(a, b), a) -> a
1253 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
1254 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
1257 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
1258 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
1263 // MAX(~a, ~b) -> ~MIN(a, b)
1264 if (SPF == SPF_SMAX || SPF == SPF_UMAX) {
1265 if (IsFreeToInvert(LHS, LHS->hasNUses(2)) &&
1266 IsFreeToInvert(RHS, RHS->hasNUses(2))) {
1268 // This transform adds a xor operation and that extra cost needs to be
1269 // justified. We look for simplifications that will result from
1270 // applying this rule:
1273 (LHS->hasNUses(2) && match(LHS, m_Not(m_Value()))) ||
1274 (RHS->hasNUses(2) && match(RHS, m_Not(m_Value()))) ||
1275 (SI.hasOneUse() && match(*SI.user_begin(), m_Not(m_Value())));
1278 Value *NewLHS = Builder->CreateNot(LHS);
1279 Value *NewRHS = Builder->CreateNot(RHS);
1280 Value *NewCmp = SPF == SPF_SMAX
1281 ? Builder->CreateICmpSLT(NewLHS, NewRHS)
1282 : Builder->CreateICmpULT(NewLHS, NewRHS);
1284 Builder->CreateNot(Builder->CreateSelect(NewCmp, NewLHS, NewRHS));
1285 return ReplaceInstUsesWith(SI, NewSI);
1291 // ABS(-X) -> ABS(X)
1294 // See if we can fold the select into a phi node if the condition is a select.
1295 if (isa<PHINode>(SI.getCondition()))
1296 // The true/false values have to be live in the PHI predecessor's blocks.
1297 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
1298 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
1299 if (Instruction *NV = FoldOpIntoPhi(SI))
1302 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
1303 if (TrueSI->getCondition()->getType() == CondVal->getType()) {
1304 // select(C, select(C, a, b), c) -> select(C, a, c)
1305 if (TrueSI->getCondition() == CondVal) {
1306 if (SI.getTrueValue() == TrueSI->getTrueValue())
1308 SI.setOperand(1, TrueSI->getTrueValue());
1311 // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
1312 // We choose this as normal form to enable folding on the And and shortening
1313 // paths for the values (this helps GetUnderlyingObjects() for example).
1314 if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
1315 Value *And = Builder->CreateAnd(CondVal, TrueSI->getCondition());
1316 SI.setOperand(0, And);
1317 SI.setOperand(1, TrueSI->getTrueValue());
1322 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
1323 if (FalseSI->getCondition()->getType() == CondVal->getType()) {
1324 // select(C, a, select(C, b, c)) -> select(C, a, c)
1325 if (FalseSI->getCondition() == CondVal) {
1326 if (SI.getFalseValue() == FalseSI->getFalseValue())
1328 SI.setOperand(2, FalseSI->getFalseValue());
1331 // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
1332 if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
1333 Value *Or = Builder->CreateOr(CondVal, FalseSI->getCondition());
1334 SI.setOperand(0, Or);
1335 SI.setOperand(2, FalseSI->getFalseValue());
1341 if (BinaryOperator::isNot(CondVal)) {
1342 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
1343 SI.setOperand(1, FalseVal);
1344 SI.setOperand(2, TrueVal);
1348 if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
1349 unsigned VWidth = VecTy->getNumElements();
1350 APInt UndefElts(VWidth, 0);
1351 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
1352 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
1354 return ReplaceInstUsesWith(SI, V);
1358 if (isa<ConstantAggregateZero>(CondVal)) {
1359 return ReplaceInstUsesWith(SI, FalseVal);