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/IR/PatternMatch.h"
19 using namespace PatternMatch;
21 #define DEBUG_TYPE "instcombine"
23 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
24 /// returning the kind and providing the out parameter results if we
25 /// successfully match.
26 static SelectPatternFlavor
27 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
28 SelectInst *SI = dyn_cast<SelectInst>(V);
29 if (!SI) return SPF_UNKNOWN;
31 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
32 if (!ICI) return SPF_UNKNOWN;
34 ICmpInst::Predicate Pred = ICI->getPredicate();
35 Value *CmpLHS = ICI->getOperand(0);
36 Value *CmpRHS = ICI->getOperand(1);
37 Value *TrueVal = SI->getTrueValue();
38 Value *FalseVal = SI->getFalseValue();
43 // (icmp X, Y) ? X : Y
44 if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
46 default: return SPF_UNKNOWN; // Equality.
47 case ICmpInst::ICMP_UGT:
48 case ICmpInst::ICMP_UGE: return SPF_UMAX;
49 case ICmpInst::ICMP_SGT:
50 case ICmpInst::ICMP_SGE: return SPF_SMAX;
51 case ICmpInst::ICMP_ULT:
52 case ICmpInst::ICMP_ULE: return SPF_UMIN;
53 case ICmpInst::ICMP_SLT:
54 case ICmpInst::ICMP_SLE: return SPF_SMIN;
58 // (icmp X, Y) ? Y : X
59 if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
61 default: return SPF_UNKNOWN; // Equality.
62 case ICmpInst::ICMP_UGT:
63 case ICmpInst::ICMP_UGE: return SPF_UMIN;
64 case ICmpInst::ICMP_SGT:
65 case ICmpInst::ICMP_SGE: return SPF_SMIN;
66 case ICmpInst::ICMP_ULT:
67 case ICmpInst::ICMP_ULE: return SPF_UMAX;
68 case ICmpInst::ICMP_SLT:
69 case ICmpInst::ICMP_SLE: return SPF_SMAX;
73 if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
74 if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
75 (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
77 // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
78 // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
79 if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
80 return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
83 // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
84 // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
85 if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
86 return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
91 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
97 /// GetSelectFoldableOperands - We want to turn code that looks like this:
99 /// %D = select %cond, %C, %A
101 /// %C = select %cond, %B, 0
104 /// Assuming that the specified instruction is an operand to the select, return
105 /// a bitmask indicating which operands of this instruction are foldable if they
106 /// equal the other incoming value of the select.
108 static unsigned GetSelectFoldableOperands(Instruction *I) {
109 switch (I->getOpcode()) {
110 case Instruction::Add:
111 case Instruction::Mul:
112 case Instruction::And:
113 case Instruction::Or:
114 case Instruction::Xor:
115 return 3; // Can fold through either operand.
116 case Instruction::Sub: // Can only fold on the amount subtracted.
117 case Instruction::Shl: // Can only fold on the shift amount.
118 case Instruction::LShr:
119 case Instruction::AShr:
122 return 0; // Cannot fold
126 /// GetSelectFoldableConstant - For the same transformation as the previous
127 /// function, return the identity constant that goes into the select.
128 static Constant *GetSelectFoldableConstant(Instruction *I) {
129 switch (I->getOpcode()) {
130 default: llvm_unreachable("This cannot happen!");
131 case Instruction::Add:
132 case Instruction::Sub:
133 case Instruction::Or:
134 case Instruction::Xor:
135 case Instruction::Shl:
136 case Instruction::LShr:
137 case Instruction::AShr:
138 return Constant::getNullValue(I->getType());
139 case Instruction::And:
140 return Constant::getAllOnesValue(I->getType());
141 case Instruction::Mul:
142 return ConstantInt::get(I->getType(), 1);
146 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
147 /// have the same opcode and only one use each. Try to simplify this.
148 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
150 if (TI->getNumOperands() == 1) {
151 // If this is a non-volatile load or a cast from the same type,
154 Type *FIOpndTy = FI->getOperand(0)->getType();
155 if (TI->getOperand(0)->getType() != FIOpndTy)
157 // The select condition may be a vector. We may only change the operand
158 // type if the vector width remains the same (and matches the condition).
159 Type *CondTy = SI.getCondition()->getType();
160 if (CondTy->isVectorTy() && (!FIOpndTy->isVectorTy() ||
161 CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()))
164 return nullptr; // unknown unary op.
167 // Fold this by inserting a select from the input values.
168 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
169 FI->getOperand(0), SI.getName()+".v");
170 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
174 // Only handle binary operators here.
175 if (!isa<BinaryOperator>(TI))
178 // Figure out if the operations have any operands in common.
179 Value *MatchOp, *OtherOpT, *OtherOpF;
181 if (TI->getOperand(0) == FI->getOperand(0)) {
182 MatchOp = TI->getOperand(0);
183 OtherOpT = TI->getOperand(1);
184 OtherOpF = FI->getOperand(1);
185 MatchIsOpZero = true;
186 } else if (TI->getOperand(1) == FI->getOperand(1)) {
187 MatchOp = TI->getOperand(1);
188 OtherOpT = TI->getOperand(0);
189 OtherOpF = FI->getOperand(0);
190 MatchIsOpZero = false;
191 } else if (!TI->isCommutative()) {
193 } else if (TI->getOperand(0) == FI->getOperand(1)) {
194 MatchOp = TI->getOperand(0);
195 OtherOpT = TI->getOperand(1);
196 OtherOpF = FI->getOperand(0);
197 MatchIsOpZero = true;
198 } else if (TI->getOperand(1) == FI->getOperand(0)) {
199 MatchOp = TI->getOperand(1);
200 OtherOpT = TI->getOperand(0);
201 OtherOpF = FI->getOperand(1);
202 MatchIsOpZero = true;
207 // If we reach here, they do have operations in common.
208 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
209 OtherOpF, SI.getName()+".v");
211 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
213 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
215 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
217 llvm_unreachable("Shouldn't get here");
220 static bool isSelect01(Constant *C1, Constant *C2) {
221 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
224 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
227 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
229 return C1I->isOne() || C1I->isAllOnesValue() ||
230 C2I->isOne() || C2I->isAllOnesValue();
233 /// FoldSelectIntoOp - Try fold the select into one of the operands to
234 /// facilitate further optimization.
235 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
237 // See the comment above GetSelectFoldableOperands for a description of the
238 // transformation we are doing here.
239 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
240 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
241 !isa<Constant>(FalseVal)) {
242 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
243 unsigned OpToFold = 0;
244 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
246 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
251 Constant *C = GetSelectFoldableConstant(TVI);
252 Value *OOp = TVI->getOperand(2-OpToFold);
253 // Avoid creating select between 2 constants unless it's selecting
254 // between 0, 1 and -1.
255 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
256 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
257 NewSel->takeName(TVI);
258 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
259 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
261 if (isa<PossiblyExactOperator>(BO))
262 BO->setIsExact(TVI_BO->isExact());
263 if (isa<OverflowingBinaryOperator>(BO)) {
264 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
265 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
274 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
275 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
276 !isa<Constant>(TrueVal)) {
277 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
278 unsigned OpToFold = 0;
279 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
281 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
286 Constant *C = GetSelectFoldableConstant(FVI);
287 Value *OOp = FVI->getOperand(2-OpToFold);
288 // Avoid creating select between 2 constants unless it's selecting
289 // between 0, 1 and -1.
290 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
291 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
292 NewSel->takeName(FVI);
293 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
294 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
296 if (isa<PossiblyExactOperator>(BO))
297 BO->setIsExact(FVI_BO->isExact());
298 if (isa<OverflowingBinaryOperator>(BO)) {
299 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
300 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
312 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
313 /// replaced with RepOp.
314 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
315 const DataLayout *TD,
316 const TargetLibraryInfo *TLI,
318 AssumptionTracker *AT) {
319 // Trivial replacement.
323 Instruction *I = dyn_cast<Instruction>(V);
327 // If this is a binary operator, try to simplify it with the replaced op.
328 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
329 if (B->getOperand(0) == Op)
330 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
331 if (B->getOperand(1) == Op)
332 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
335 // Same for CmpInsts.
336 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
337 if (C->getOperand(0) == Op)
338 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
340 if (C->getOperand(1) == Op)
341 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
345 // TODO: We could hand off more cases to instsimplify here.
347 // If all operands are constant after substituting Op for RepOp then we can
348 // constant fold the instruction.
349 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
350 // Build a list of all constant operands.
351 SmallVector<Constant*, 8> ConstOps;
352 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
353 if (I->getOperand(i) == Op)
354 ConstOps.push_back(CRepOp);
355 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
356 ConstOps.push_back(COp);
361 // All operands were constants, fold it.
362 if (ConstOps.size() == I->getNumOperands()) {
363 if (CmpInst *C = dyn_cast<CmpInst>(I))
364 return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
365 ConstOps[1], TD, TLI);
367 if (LoadInst *LI = dyn_cast<LoadInst>(I))
368 if (!LI->isVolatile())
369 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
371 return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
379 /// foldSelectICmpAndOr - We want to turn:
380 /// (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
382 /// (or (shl (and X, C1), C3), y)
384 /// C1 and C2 are both powers of 2
386 /// C3 = Log(C2) - Log(C1)
388 /// This transform handles cases where:
389 /// 1. The icmp predicate is inverted
390 /// 2. The select operands are reversed
391 /// 3. The magnitude of C2 and C1 are flipped
392 static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
394 InstCombiner::BuilderTy *Builder) {
395 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
396 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
399 Value *CmpLHS = IC->getOperand(0);
400 Value *CmpRHS = IC->getOperand(1);
402 if (!match(CmpRHS, m_Zero()))
407 if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
411 bool OrOnTrueVal = false;
412 bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
414 OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
416 if (!OrOnFalseVal && !OrOnTrueVal)
420 Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
422 unsigned C1Log = C1->logBase2();
423 unsigned C2Log = C2->logBase2();
425 V = Builder->CreateZExtOrTrunc(V, Y->getType());
426 V = Builder->CreateShl(V, C2Log - C1Log);
427 } else if (C1Log > C2Log) {
428 V = Builder->CreateLShr(V, C1Log - C2Log);
429 V = Builder->CreateZExtOrTrunc(V, Y->getType());
431 V = Builder->CreateZExtOrTrunc(V, Y->getType());
433 ICmpInst::Predicate Pred = IC->getPredicate();
434 if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
435 (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
436 V = Builder->CreateXor(V, *C2);
438 return Builder->CreateOr(V, Y);
441 /// visitSelectInstWithICmp - Visit a SelectInst that has an
442 /// ICmpInst as its first operand.
444 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
446 bool Changed = false;
447 ICmpInst::Predicate Pred = ICI->getPredicate();
448 Value *CmpLHS = ICI->getOperand(0);
449 Value *CmpRHS = ICI->getOperand(1);
450 Value *TrueVal = SI.getTrueValue();
451 Value *FalseVal = SI.getFalseValue();
453 // Check cases where the comparison is with a constant that
454 // can be adjusted to fit the min/max idiom. We may move or edit ICI
455 // here, so make sure the select is the only user.
456 if (ICI->hasOneUse())
457 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
458 // X < MIN ? T : F --> F
459 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
460 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
461 return ReplaceInstUsesWith(SI, FalseVal);
462 // X > MAX ? T : F --> F
463 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
464 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
465 return ReplaceInstUsesWith(SI, FalseVal);
468 case ICmpInst::ICMP_ULT:
469 case ICmpInst::ICMP_SLT:
470 case ICmpInst::ICMP_UGT:
471 case ICmpInst::ICMP_SGT: {
472 // These transformations only work for selects over integers.
473 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
477 Constant *AdjustedRHS;
478 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
479 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
480 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
481 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
483 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
484 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
485 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
486 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
487 ; // Nothing to do here. Values match without any sign/zero extension.
489 // Types do not match. Instead of calculating this with mixed types
490 // promote all to the larger type. This enables scalar evolution to
491 // analyze this expression.
492 else if (CmpRHS->getType()->getScalarSizeInBits()
493 < SelectTy->getBitWidth()) {
494 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
496 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
497 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
498 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
499 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
500 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
501 sextRHS == FalseVal) {
503 AdjustedRHS = sextRHS;
504 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
505 sextRHS == TrueVal) {
507 AdjustedRHS = sextRHS;
508 } else if (ICI->isUnsigned()) {
509 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
510 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
511 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
512 // zext + signed compare cannot be changed:
513 // 0xff <s 0x00, but 0x00ff >s 0x0000
514 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
515 zextRHS == FalseVal) {
517 AdjustedRHS = zextRHS;
518 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
519 zextRHS == TrueVal) {
521 AdjustedRHS = zextRHS;
529 Pred = ICmpInst::getSwappedPredicate(Pred);
530 CmpRHS = AdjustedRHS;
531 std::swap(FalseVal, TrueVal);
532 ICI->setPredicate(Pred);
533 ICI->setOperand(0, CmpLHS);
534 ICI->setOperand(1, CmpRHS);
535 SI.setOperand(1, TrueVal);
536 SI.setOperand(2, FalseVal);
538 // Move ICI instruction right before the select instruction. Otherwise
539 // the sext/zext value may be defined after the ICI instruction uses it.
540 ICI->moveBefore(&SI);
548 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
549 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
550 // FIXME: Type and constness constraints could be lifted, but we have to
551 // watch code size carefully. We should consider xor instead of
552 // sub/add when we decide to do that.
553 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
554 if (TrueVal->getType() == Ty) {
555 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
556 ConstantInt *C1 = nullptr, *C2 = nullptr;
557 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
558 C1 = dyn_cast<ConstantInt>(TrueVal);
559 C2 = dyn_cast<ConstantInt>(FalseVal);
560 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
561 C1 = dyn_cast<ConstantInt>(FalseVal);
562 C2 = dyn_cast<ConstantInt>(TrueVal);
565 // This shift results in either -1 or 0.
566 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
568 // Check if we can express the operation with a single or.
569 if (C2->isAllOnesValue())
570 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
572 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
573 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
579 // If we have an equality comparison then we know the value in one of the
580 // arms of the select. See if substituting this value into the arm and
581 // simplifying the result yields the same value as the other arm.
582 if (Pred == ICmpInst::ICMP_EQ) {
583 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI,
584 DT, AT) == TrueVal ||
585 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI,
587 return ReplaceInstUsesWith(SI, FalseVal);
588 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI,
589 DT, AT) == FalseVal ||
590 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI,
592 return ReplaceInstUsesWith(SI, FalseVal);
593 } else if (Pred == ICmpInst::ICMP_NE) {
594 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI,
595 DT, AT) == FalseVal ||
596 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI,
598 return ReplaceInstUsesWith(SI, TrueVal);
599 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI,
600 DT, AT) == TrueVal ||
601 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI,
603 return ReplaceInstUsesWith(SI, TrueVal);
606 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
608 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
609 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
610 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
611 SI.setOperand(1, CmpRHS);
613 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
614 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
615 SI.setOperand(2, CmpRHS);
620 if (unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits()) {
621 APInt MinSignedValue = APInt::getSignBit(BitWidth);
625 bool IsBitTest = false;
626 if (ICmpInst::isEquality(Pred) &&
627 match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
628 match(CmpRHS, m_Zero())) {
630 TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
631 } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
635 TrueWhenUnset = false;
636 } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
640 TrueWhenUnset = true;
644 // (X & Y) == 0 ? X : X ^ Y --> X & ~Y
645 if (TrueWhenUnset && TrueVal == X &&
646 match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
647 V = Builder->CreateAnd(X, ~(*Y));
648 // (X & Y) != 0 ? X ^ Y : X --> X & ~Y
649 else if (!TrueWhenUnset && FalseVal == X &&
650 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
651 V = Builder->CreateAnd(X, ~(*Y));
652 // (X & Y) == 0 ? X ^ Y : X --> X | Y
653 else if (TrueWhenUnset && FalseVal == X &&
654 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
655 V = Builder->CreateOr(X, *Y);
656 // (X & Y) != 0 ? X : X ^ Y --> X | Y
657 else if (!TrueWhenUnset && TrueVal == X &&
658 match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
659 V = Builder->CreateOr(X, *Y);
662 return ReplaceInstUsesWith(SI, V);
666 if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
667 return ReplaceInstUsesWith(SI, V);
669 return Changed ? &SI : nullptr;
673 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
674 /// PHI node (but the two may be in different blocks). See if the true/false
675 /// values (V) are live in all of the predecessor blocks of the PHI. For
676 /// example, cases like this cannot be mapped:
678 /// X = phi [ C1, BB1], [C2, BB2]
680 /// Z = select X, Y, 0
682 /// because Y is not live in BB1/BB2.
684 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
685 const SelectInst &SI) {
686 // If the value is a non-instruction value like a constant or argument, it
687 // can always be mapped.
688 const Instruction *I = dyn_cast<Instruction>(V);
691 // If V is a PHI node defined in the same block as the condition PHI, we can
692 // map the arguments.
693 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
695 if (const PHINode *VP = dyn_cast<PHINode>(I))
696 if (VP->getParent() == CondPHI->getParent())
699 // Otherwise, if the PHI and select are defined in the same block and if V is
700 // defined in a different block, then we can transform it.
701 if (SI.getParent() == CondPHI->getParent() &&
702 I->getParent() != CondPHI->getParent())
705 // Otherwise we have a 'hard' case and we can't tell without doing more
706 // detailed dominator based analysis, punt.
710 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
711 /// SPF2(SPF1(A, B), C)
712 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
713 SelectPatternFlavor SPF1,
716 SelectPatternFlavor SPF2, Value *C) {
717 if (C == A || C == B) {
718 // MAX(MAX(A, B), B) -> MAX(A, B)
719 // MIN(MIN(a, b), a) -> MIN(a, b)
721 return ReplaceInstUsesWith(Outer, Inner);
723 // MAX(MIN(a, b), a) -> a
724 // MIN(MAX(a, b), a) -> a
725 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
726 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
727 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
728 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
729 return ReplaceInstUsesWith(Outer, C);
733 if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
734 if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
735 APInt ACB = CB->getValue();
736 APInt ACC = CC->getValue();
738 // MIN(MIN(A, 23), 97) -> MIN(A, 23)
739 // MAX(MAX(A, 97), 23) -> MAX(A, 97)
740 if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
741 (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
742 (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
743 (SPF1 == SPF_SMAX && ACB.sge(ACC)))
744 return ReplaceInstUsesWith(Outer, Inner);
746 // MIN(MIN(A, 97), 23) -> MIN(A, 23)
747 // MAX(MAX(A, 23), 97) -> MAX(A, 97)
748 if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
749 (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
750 (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
751 (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
752 Outer.replaceUsesOfWith(Inner, A);
759 // ABS(ABS(X)) -> ABS(X)
760 // NABS(NABS(X)) -> NABS(X)
761 if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
762 return ReplaceInstUsesWith(Outer, Inner);
765 // ABS(NABS(X)) -> ABS(X)
766 // NABS(ABS(X)) -> NABS(X)
767 if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
768 (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
769 SelectInst *SI = cast<SelectInst>(Inner);
770 Value *NewSI = Builder->CreateSelect(
771 SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
772 return ReplaceInstUsesWith(Outer, NewSI);
777 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
778 /// both be) and we have an icmp instruction with zero, and we have an 'and'
779 /// with the non-constant value and a power of two we can turn the select
780 /// into a shift on the result of the 'and'.
781 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
782 ConstantInt *FalseVal,
783 InstCombiner::BuilderTy *Builder) {
784 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
785 if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
788 if (!match(IC->getOperand(1), m_Zero()))
792 Value *LHS = IC->getOperand(0);
793 if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
796 // If both select arms are non-zero see if we have a select of the form
797 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
798 // for 'x ? 2^n : 0' and fix the thing up at the end.
799 ConstantInt *Offset = nullptr;
800 if (!TrueVal->isZero() && !FalseVal->isZero()) {
801 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
803 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
808 // Adjust TrueVal and FalseVal to the offset.
809 TrueVal = ConstantInt::get(Builder->getContext(),
810 TrueVal->getValue() - Offset->getValue());
811 FalseVal = ConstantInt::get(Builder->getContext(),
812 FalseVal->getValue() - Offset->getValue());
815 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
816 if (!AndRHS->getValue().isPowerOf2() ||
817 (!TrueVal->getValue().isPowerOf2() &&
818 !FalseVal->getValue().isPowerOf2()))
821 // Determine which shift is needed to transform result of the 'and' into the
823 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
824 unsigned ValZeros = ValC->getValue().logBase2();
825 unsigned AndZeros = AndRHS->getValue().logBase2();
827 // If types don't match we can still convert the select by introducing a zext
828 // or a trunc of the 'and'. The trunc case requires that all of the truncated
829 // bits are zero, we can figure that out by looking at the 'and' mask.
830 if (AndZeros >= ValC->getBitWidth())
833 Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
834 if (ValZeros > AndZeros)
835 V = Builder->CreateShl(V, ValZeros - AndZeros);
836 else if (ValZeros < AndZeros)
837 V = Builder->CreateLShr(V, AndZeros - ValZeros);
839 // Okay, now we know that everything is set up, we just don't know whether we
840 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
841 bool ShouldNotVal = !TrueVal->isZero();
842 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
844 V = Builder->CreateXor(V, ValC);
846 // Apply an offset if needed.
848 V = Builder->CreateAdd(V, Offset);
852 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
853 Value *CondVal = SI.getCondition();
854 Value *TrueVal = SI.getTrueValue();
855 Value *FalseVal = SI.getFalseValue();
857 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, DL, TLI,
859 return ReplaceInstUsesWith(SI, V);
861 if (SI.getType()->isIntegerTy(1)) {
862 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
863 if (C->getZExtValue()) {
864 // Change: A = select B, true, C --> A = or B, C
865 return BinaryOperator::CreateOr(CondVal, FalseVal);
867 // Change: A = select B, false, C --> A = and !B, C
868 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
869 return BinaryOperator::CreateAnd(NotCond, FalseVal);
871 if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
872 if (C->getZExtValue() == false) {
873 // Change: A = select B, C, false --> A = and B, C
874 return BinaryOperator::CreateAnd(CondVal, TrueVal);
876 // Change: A = select B, C, true --> A = or !B, C
877 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
878 return BinaryOperator::CreateOr(NotCond, TrueVal);
881 // select a, b, a -> a&b
882 // select a, a, b -> a|b
883 if (CondVal == TrueVal)
884 return BinaryOperator::CreateOr(CondVal, FalseVal);
885 if (CondVal == FalseVal)
886 return BinaryOperator::CreateAnd(CondVal, TrueVal);
888 // select a, ~a, b -> (~a)&b
889 // select a, b, ~a -> (~a)|b
890 if (match(TrueVal, m_Not(m_Specific(CondVal))))
891 return BinaryOperator::CreateAnd(TrueVal, FalseVal);
892 if (match(FalseVal, m_Not(m_Specific(CondVal))))
893 return BinaryOperator::CreateOr(TrueVal, FalseVal);
896 // Selecting between two integer constants?
897 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
898 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
899 // select C, 1, 0 -> zext C to int
900 if (FalseValC->isZero() && TrueValC->getValue() == 1)
901 return new ZExtInst(CondVal, SI.getType());
903 // select C, -1, 0 -> sext C to int
904 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
905 return new SExtInst(CondVal, SI.getType());
907 // select C, 0, 1 -> zext !C to int
908 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
909 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
910 return new ZExtInst(NotCond, SI.getType());
913 // select C, 0, -1 -> sext !C to int
914 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
915 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
916 return new SExtInst(NotCond, SI.getType());
919 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
920 return ReplaceInstUsesWith(SI, V);
923 // See if we are selecting two values based on a comparison of the two values.
924 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
925 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
926 // Transform (X == Y) ? X : Y -> Y
927 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
928 // This is not safe in general for floating point:
929 // consider X== -0, Y== +0.
930 // It becomes safe if either operand is a nonzero constant.
931 ConstantFP *CFPt, *CFPf;
932 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
933 !CFPt->getValueAPF().isZero()) ||
934 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
935 !CFPf->getValueAPF().isZero()))
936 return ReplaceInstUsesWith(SI, FalseVal);
938 // Transform (X une Y) ? X : Y -> X
939 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
940 // This is not safe in general for floating point:
941 // consider X== -0, Y== +0.
942 // It becomes safe if either operand is a nonzero constant.
943 ConstantFP *CFPt, *CFPf;
944 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
945 !CFPt->getValueAPF().isZero()) ||
946 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
947 !CFPf->getValueAPF().isZero()))
948 return ReplaceInstUsesWith(SI, TrueVal);
951 // Canonicalize to use ordered comparisons by swapping the select
955 // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
956 if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
957 FCmpInst::Predicate InvPred = FCI->getInversePredicate();
958 Value *NewCond = Builder->CreateFCmp(InvPred, TrueVal, FalseVal,
959 FCI->getName() + ".inv");
961 return SelectInst::Create(NewCond, FalseVal, TrueVal,
962 SI.getName() + ".p");
965 // NOTE: if we wanted to, this is where to detect MIN/MAX
966 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
967 // Transform (X == Y) ? Y : X -> X
968 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
969 // This is not safe in general for floating point:
970 // consider X== -0, Y== +0.
971 // It becomes safe if either operand is a nonzero constant.
972 ConstantFP *CFPt, *CFPf;
973 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
974 !CFPt->getValueAPF().isZero()) ||
975 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
976 !CFPf->getValueAPF().isZero()))
977 return ReplaceInstUsesWith(SI, FalseVal);
979 // Transform (X une Y) ? Y : X -> Y
980 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
981 // This is not safe in general for floating point:
982 // consider X== -0, Y== +0.
983 // It becomes safe if either operand is a nonzero constant.
984 ConstantFP *CFPt, *CFPf;
985 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
986 !CFPt->getValueAPF().isZero()) ||
987 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
988 !CFPf->getValueAPF().isZero()))
989 return ReplaceInstUsesWith(SI, TrueVal);
992 // Canonicalize to use ordered comparisons by swapping the select
996 // (X ugt Y) ? X : Y -> (X ole Y) ? X : Y
997 if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
998 FCmpInst::Predicate InvPred = FCI->getInversePredicate();
999 Value *NewCond = Builder->CreateFCmp(InvPred, FalseVal, TrueVal,
1000 FCI->getName() + ".inv");
1002 return SelectInst::Create(NewCond, FalseVal, TrueVal,
1003 SI.getName() + ".p");
1006 // NOTE: if we wanted to, this is where to detect MIN/MAX
1008 // NOTE: if we wanted to, this is where to detect ABS
1011 // See if we are selecting two values based on a comparison of the two values.
1012 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
1013 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
1016 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
1017 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
1018 if (TI->hasOneUse() && FI->hasOneUse()) {
1019 Instruction *AddOp = nullptr, *SubOp = nullptr;
1021 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
1022 if (TI->getOpcode() == FI->getOpcode())
1023 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
1026 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
1027 // even legal for FP.
1028 if ((TI->getOpcode() == Instruction::Sub &&
1029 FI->getOpcode() == Instruction::Add) ||
1030 (TI->getOpcode() == Instruction::FSub &&
1031 FI->getOpcode() == Instruction::FAdd)) {
1032 AddOp = FI; SubOp = TI;
1033 } else if ((FI->getOpcode() == Instruction::Sub &&
1034 TI->getOpcode() == Instruction::Add) ||
1035 (FI->getOpcode() == Instruction::FSub &&
1036 TI->getOpcode() == Instruction::FAdd)) {
1037 AddOp = TI; SubOp = FI;
1041 Value *OtherAddOp = nullptr;
1042 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
1043 OtherAddOp = AddOp->getOperand(1);
1044 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
1045 OtherAddOp = AddOp->getOperand(0);
1049 // So at this point we know we have (Y -> OtherAddOp):
1050 // select C, (add X, Y), (sub X, Z)
1051 Value *NegVal; // Compute -Z
1052 if (SI.getType()->isFPOrFPVectorTy()) {
1053 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
1054 if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
1055 FastMathFlags Flags = AddOp->getFastMathFlags();
1056 Flags &= SubOp->getFastMathFlags();
1057 NegInst->setFastMathFlags(Flags);
1060 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
1063 Value *NewTrueOp = OtherAddOp;
1064 Value *NewFalseOp = NegVal;
1066 std::swap(NewTrueOp, NewFalseOp);
1068 Builder->CreateSelect(CondVal, NewTrueOp,
1069 NewFalseOp, SI.getName() + ".p");
1071 if (SI.getType()->isFPOrFPVectorTy()) {
1073 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
1075 FastMathFlags Flags = AddOp->getFastMathFlags();
1076 Flags &= SubOp->getFastMathFlags();
1077 RI->setFastMathFlags(Flags);
1080 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
1085 // See if we can fold the select into one of our operands.
1086 if (SI.getType()->isIntegerTy()) {
1087 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
1090 // MAX(MAX(a, b), a) -> MAX(a, b)
1091 // MIN(MIN(a, b), a) -> MIN(a, b)
1092 // MAX(MIN(a, b), a) -> a
1093 // MIN(MAX(a, b), a) -> a
1094 Value *LHS, *RHS, *LHS2, *RHS2;
1095 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
1096 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
1097 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
1100 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
1101 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
1107 // ABS(-X) -> ABS(X)
1110 // See if we can fold the select into a phi node if the condition is a select.
1111 if (isa<PHINode>(SI.getCondition()))
1112 // The true/false values have to be live in the PHI predecessor's blocks.
1113 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
1114 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
1115 if (Instruction *NV = FoldOpIntoPhi(SI))
1118 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
1119 if (TrueSI->getCondition() == CondVal) {
1120 if (SI.getTrueValue() == TrueSI->getTrueValue())
1122 SI.setOperand(1, TrueSI->getTrueValue());
1126 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
1127 if (FalseSI->getCondition() == CondVal) {
1128 if (SI.getFalseValue() == FalseSI->getFalseValue())
1130 SI.setOperand(2, FalseSI->getFalseValue());
1135 if (BinaryOperator::isNot(CondVal)) {
1136 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
1137 SI.setOperand(1, FalseVal);
1138 SI.setOperand(2, TrueVal);
1142 if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
1143 unsigned VWidth = VecTy->getNumElements();
1144 APInt UndefElts(VWidth, 0);
1145 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
1146 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
1148 return ReplaceInstUsesWith(SI, V);
1152 if (isa<ConstantAggregateZero>(CondVal)) {
1153 return ReplaceInstUsesWith(SI, FalseVal);