1 //===- InstCombineSelect.cpp ----------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the visitSelect function.
12 //===----------------------------------------------------------------------===//
14 #include "InstCombine.h"
15 #include "llvm/Support/PatternMatch.h"
16 #include "llvm/Analysis/ConstantFolding.h"
17 #include "llvm/Analysis/InstructionSimplify.h"
19 using namespace PatternMatch;
21 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
22 /// returning the kind and providing the out parameter results if we
23 /// successfully match.
24 static SelectPatternFlavor
25 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
26 SelectInst *SI = dyn_cast<SelectInst>(V);
27 if (SI == 0) return SPF_UNKNOWN;
29 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
30 if (ICI == 0) return SPF_UNKNOWN;
32 LHS = ICI->getOperand(0);
33 RHS = ICI->getOperand(1);
35 // (icmp X, Y) ? X : Y
36 if (SI->getTrueValue() == ICI->getOperand(0) &&
37 SI->getFalseValue() == ICI->getOperand(1)) {
38 switch (ICI->getPredicate()) {
39 default: return SPF_UNKNOWN; // Equality.
40 case ICmpInst::ICMP_UGT:
41 case ICmpInst::ICMP_UGE: return SPF_UMAX;
42 case ICmpInst::ICMP_SGT:
43 case ICmpInst::ICMP_SGE: return SPF_SMAX;
44 case ICmpInst::ICMP_ULT:
45 case ICmpInst::ICMP_ULE: return SPF_UMIN;
46 case ICmpInst::ICMP_SLT:
47 case ICmpInst::ICMP_SLE: return SPF_SMIN;
51 // (icmp X, Y) ? Y : X
52 if (SI->getTrueValue() == ICI->getOperand(1) &&
53 SI->getFalseValue() == ICI->getOperand(0)) {
54 switch (ICI->getPredicate()) {
55 default: return SPF_UNKNOWN; // Equality.
56 case ICmpInst::ICMP_UGT:
57 case ICmpInst::ICMP_UGE: return SPF_UMIN;
58 case ICmpInst::ICMP_SGT:
59 case ICmpInst::ICMP_SGE: return SPF_SMIN;
60 case ICmpInst::ICMP_ULT:
61 case ICmpInst::ICMP_ULE: return SPF_UMAX;
62 case ICmpInst::ICMP_SLT:
63 case ICmpInst::ICMP_SLE: return SPF_SMAX;
67 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
73 /// GetSelectFoldableOperands - We want to turn code that looks like this:
75 /// %D = select %cond, %C, %A
77 /// %C = select %cond, %B, 0
80 /// Assuming that the specified instruction is an operand to the select, return
81 /// a bitmask indicating which operands of this instruction are foldable if they
82 /// equal the other incoming value of the select.
84 static unsigned GetSelectFoldableOperands(Instruction *I) {
85 switch (I->getOpcode()) {
86 case Instruction::Add:
87 case Instruction::Mul:
88 case Instruction::And:
90 case Instruction::Xor:
91 return 3; // Can fold through either operand.
92 case Instruction::Sub: // Can only fold on the amount subtracted.
93 case Instruction::Shl: // Can only fold on the shift amount.
94 case Instruction::LShr:
95 case Instruction::AShr:
98 return 0; // Cannot fold
102 /// GetSelectFoldableConstant - For the same transformation as the previous
103 /// function, return the identity constant that goes into the select.
104 static Constant *GetSelectFoldableConstant(Instruction *I) {
105 switch (I->getOpcode()) {
106 default: llvm_unreachable("This cannot happen!");
107 case Instruction::Add:
108 case Instruction::Sub:
109 case Instruction::Or:
110 case Instruction::Xor:
111 case Instruction::Shl:
112 case Instruction::LShr:
113 case Instruction::AShr:
114 return Constant::getNullValue(I->getType());
115 case Instruction::And:
116 return Constant::getAllOnesValue(I->getType());
117 case Instruction::Mul:
118 return ConstantInt::get(I->getType(), 1);
122 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
123 /// have the same opcode and only one use each. Try to simplify this.
124 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
126 if (TI->getNumOperands() == 1) {
127 // If this is a non-volatile load or a cast from the same type,
130 if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
132 // The select condition may be a vector. We may only change the operand
133 // type if the vector width remains the same (and matches the condition).
134 Type *CondTy = SI.getCondition()->getType();
135 if (CondTy->isVectorTy() && CondTy->getVectorNumElements() !=
136 FI->getOperand(0)->getType()->getVectorNumElements())
139 return 0; // unknown unary op.
142 // Fold this by inserting a select from the input values.
143 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
144 FI->getOperand(0), SI.getName()+".v");
145 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
149 // Only handle binary operators here.
150 if (!isa<BinaryOperator>(TI))
153 // Figure out if the operations have any operands in common.
154 Value *MatchOp, *OtherOpT, *OtherOpF;
156 if (TI->getOperand(0) == FI->getOperand(0)) {
157 MatchOp = TI->getOperand(0);
158 OtherOpT = TI->getOperand(1);
159 OtherOpF = FI->getOperand(1);
160 MatchIsOpZero = true;
161 } else if (TI->getOperand(1) == FI->getOperand(1)) {
162 MatchOp = TI->getOperand(1);
163 OtherOpT = TI->getOperand(0);
164 OtherOpF = FI->getOperand(0);
165 MatchIsOpZero = false;
166 } else if (!TI->isCommutative()) {
168 } else if (TI->getOperand(0) == FI->getOperand(1)) {
169 MatchOp = TI->getOperand(0);
170 OtherOpT = TI->getOperand(1);
171 OtherOpF = FI->getOperand(0);
172 MatchIsOpZero = true;
173 } else if (TI->getOperand(1) == FI->getOperand(0)) {
174 MatchOp = TI->getOperand(1);
175 OtherOpT = TI->getOperand(0);
176 OtherOpF = FI->getOperand(1);
177 MatchIsOpZero = true;
182 // If we reach here, they do have operations in common.
183 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
184 OtherOpF, SI.getName()+".v");
186 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
188 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
190 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
192 llvm_unreachable("Shouldn't get here");
195 static bool isSelect01(Constant *C1, Constant *C2) {
196 ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
199 ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
202 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
204 return C1I->isOne() || C1I->isAllOnesValue() ||
205 C2I->isOne() || C2I->isAllOnesValue();
208 /// FoldSelectIntoOp - Try fold the select into one of the operands to
209 /// facilitate further optimization.
210 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
212 // See the comment above GetSelectFoldableOperands for a description of the
213 // transformation we are doing here.
214 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
215 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
216 !isa<Constant>(FalseVal)) {
217 if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
218 unsigned OpToFold = 0;
219 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
221 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
226 Constant *C = GetSelectFoldableConstant(TVI);
227 Value *OOp = TVI->getOperand(2-OpToFold);
228 // Avoid creating select between 2 constants unless it's selecting
229 // between 0, 1 and -1.
230 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
231 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
232 NewSel->takeName(TVI);
233 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
234 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
236 if (isa<PossiblyExactOperator>(BO))
237 BO->setIsExact(TVI_BO->isExact());
238 if (isa<OverflowingBinaryOperator>(BO)) {
239 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
240 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
249 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
250 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
251 !isa<Constant>(TrueVal)) {
252 if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
253 unsigned OpToFold = 0;
254 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
256 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
261 Constant *C = GetSelectFoldableConstant(FVI);
262 Value *OOp = FVI->getOperand(2-OpToFold);
263 // Avoid creating select between 2 constants unless it's selecting
264 // between 0, 1 and -1.
265 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
266 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
267 NewSel->takeName(FVI);
268 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
269 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
271 if (isa<PossiblyExactOperator>(BO))
272 BO->setIsExact(FVI_BO->isExact());
273 if (isa<OverflowingBinaryOperator>(BO)) {
274 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
275 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
287 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
288 /// replaced with RepOp.
289 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
290 const DataLayout *TD,
291 const TargetLibraryInfo *TLI) {
292 // Trivial replacement.
296 Instruction *I = dyn_cast<Instruction>(V);
300 // If this is a binary operator, try to simplify it with the replaced op.
301 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
302 if (B->getOperand(0) == Op)
303 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
304 if (B->getOperand(1) == Op)
305 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
308 // Same for CmpInsts.
309 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
310 if (C->getOperand(0) == Op)
311 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
313 if (C->getOperand(1) == Op)
314 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
318 // TODO: We could hand off more cases to instsimplify here.
320 // If all operands are constant after substituting Op for RepOp then we can
321 // constant fold the instruction.
322 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
323 // Build a list of all constant operands.
324 SmallVector<Constant*, 8> ConstOps;
325 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
326 if (I->getOperand(i) == Op)
327 ConstOps.push_back(CRepOp);
328 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
329 ConstOps.push_back(COp);
334 // All operands were constants, fold it.
335 if (ConstOps.size() == I->getNumOperands()) {
336 if (CmpInst *C = dyn_cast<CmpInst>(I))
337 return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
338 ConstOps[1], TD, TLI);
340 if (LoadInst *LI = dyn_cast<LoadInst>(I))
341 if (!LI->isVolatile())
342 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
344 return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
352 /// visitSelectInstWithICmp - Visit a SelectInst that has an
353 /// ICmpInst as its first operand.
355 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
357 bool Changed = false;
358 ICmpInst::Predicate Pred = ICI->getPredicate();
359 Value *CmpLHS = ICI->getOperand(0);
360 Value *CmpRHS = ICI->getOperand(1);
361 Value *TrueVal = SI.getTrueValue();
362 Value *FalseVal = SI.getFalseValue();
364 // Check cases where the comparison is with a constant that
365 // can be adjusted to fit the min/max idiom. We may move or edit ICI
366 // here, so make sure the select is the only user.
367 if (ICI->hasOneUse())
368 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
369 // X < MIN ? T : F --> F
370 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
371 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
372 return ReplaceInstUsesWith(SI, FalseVal);
373 // X > MAX ? T : F --> F
374 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
375 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
376 return ReplaceInstUsesWith(SI, FalseVal);
379 case ICmpInst::ICMP_ULT:
380 case ICmpInst::ICMP_SLT:
381 case ICmpInst::ICMP_UGT:
382 case ICmpInst::ICMP_SGT: {
383 // These transformations only work for selects over integers.
384 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
388 Constant *AdjustedRHS;
389 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
390 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
391 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
392 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
394 // X > C ? X : C+1 --> X < C+1 ? C+1 : X
395 // X < C ? X : C-1 --> X > C-1 ? C-1 : X
396 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
397 (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
398 ; // Nothing to do here. Values match without any sign/zero extension.
400 // Types do not match. Instead of calculating this with mixed types
401 // promote all to the larger type. This enables scalar evolution to
402 // analyze this expression.
403 else if (CmpRHS->getType()->getScalarSizeInBits()
404 < SelectTy->getBitWidth()) {
405 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
407 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
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 >u c ? X : C+1 --> X = sext x; X <u 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 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
412 sextRHS == FalseVal) {
414 AdjustedRHS = sextRHS;
415 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
416 sextRHS == TrueVal) {
418 AdjustedRHS = sextRHS;
419 } else if (ICI->isUnsigned()) {
420 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
421 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
422 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
423 // zext + signed compare cannot be changed:
424 // 0xff <s 0x00, but 0x00ff >s 0x0000
425 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
426 zextRHS == FalseVal) {
428 AdjustedRHS = zextRHS;
429 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
430 zextRHS == TrueVal) {
432 AdjustedRHS = zextRHS;
440 Pred = ICmpInst::getSwappedPredicate(Pred);
441 CmpRHS = AdjustedRHS;
442 std::swap(FalseVal, TrueVal);
443 ICI->setPredicate(Pred);
444 ICI->setOperand(0, CmpLHS);
445 ICI->setOperand(1, CmpRHS);
446 SI.setOperand(1, TrueVal);
447 SI.setOperand(2, FalseVal);
449 // Move ICI instruction right before the select instruction. Otherwise
450 // the sext/zext value may be defined after the ICI instruction uses it.
451 ICI->moveBefore(&SI);
459 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
460 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
461 // FIXME: Type and constness constraints could be lifted, but we have to
462 // watch code size carefully. We should consider xor instead of
463 // sub/add when we decide to do that.
464 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
465 if (TrueVal->getType() == Ty) {
466 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
467 ConstantInt *C1 = NULL, *C2 = NULL;
468 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
469 C1 = dyn_cast<ConstantInt>(TrueVal);
470 C2 = dyn_cast<ConstantInt>(FalseVal);
471 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
472 C1 = dyn_cast<ConstantInt>(FalseVal);
473 C2 = dyn_cast<ConstantInt>(TrueVal);
476 // This shift results in either -1 or 0.
477 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
479 // Check if we can express the operation with a single or.
480 if (C2->isAllOnesValue())
481 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
483 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
484 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
490 // If we have an equality comparison then we know the value in one of the
491 // arms of the select. See if substituting this value into the arm and
492 // simplifying the result yields the same value as the other arm.
493 if (Pred == ICmpInst::ICMP_EQ) {
494 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
495 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
496 return ReplaceInstUsesWith(SI, FalseVal);
497 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
498 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
499 return ReplaceInstUsesWith(SI, FalseVal);
500 } else if (Pred == ICmpInst::ICMP_NE) {
501 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
502 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
503 return ReplaceInstUsesWith(SI, TrueVal);
504 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
505 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
506 return ReplaceInstUsesWith(SI, TrueVal);
509 // NOTE: if we wanted to, this is where to detect integer MIN/MAX
511 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
512 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
513 // Transform (X == C) ? X : Y -> (X == C) ? C : Y
514 SI.setOperand(1, CmpRHS);
516 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
517 // Transform (X != C) ? Y : X -> (X != C) ? Y : C
518 SI.setOperand(2, CmpRHS);
523 return Changed ? &SI : 0;
527 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
528 /// PHI node (but the two may be in different blocks). See if the true/false
529 /// values (V) are live in all of the predecessor blocks of the PHI. For
530 /// example, cases like this cannot be mapped:
532 /// X = phi [ C1, BB1], [C2, BB2]
534 /// Z = select X, Y, 0
536 /// because Y is not live in BB1/BB2.
538 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
539 const SelectInst &SI) {
540 // If the value is a non-instruction value like a constant or argument, it
541 // can always be mapped.
542 const Instruction *I = dyn_cast<Instruction>(V);
543 if (I == 0) return true;
545 // If V is a PHI node defined in the same block as the condition PHI, we can
546 // map the arguments.
547 const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
549 if (const PHINode *VP = dyn_cast<PHINode>(I))
550 if (VP->getParent() == CondPHI->getParent())
553 // Otherwise, if the PHI and select are defined in the same block and if V is
554 // defined in a different block, then we can transform it.
555 if (SI.getParent() == CondPHI->getParent() &&
556 I->getParent() != CondPHI->getParent())
559 // Otherwise we have a 'hard' case and we can't tell without doing more
560 // detailed dominator based analysis, punt.
564 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
565 /// SPF2(SPF1(A, B), C)
566 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
567 SelectPatternFlavor SPF1,
570 SelectPatternFlavor SPF2, Value *C) {
571 if (C == A || C == B) {
572 // MAX(MAX(A, B), B) -> MAX(A, B)
573 // MIN(MIN(a, b), a) -> MIN(a, b)
575 return ReplaceInstUsesWith(Outer, Inner);
577 // MAX(MIN(a, b), a) -> a
578 // MIN(MAX(a, b), a) -> a
579 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
580 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
581 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
582 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
583 return ReplaceInstUsesWith(Outer, C);
586 // TODO: MIN(MIN(A, 23), 97)
591 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
592 /// both be) and we have an icmp instruction with zero, and we have an 'and'
593 /// with the non-constant value and a power of two we can turn the select
594 /// into a shift on the result of the 'and'.
595 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
596 ConstantInt *FalseVal,
597 InstCombiner::BuilderTy *Builder) {
598 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
599 if (!IC || !IC->isEquality())
602 if (!match(IC->getOperand(1), m_Zero()))
606 Value *LHS = IC->getOperand(0);
607 if (LHS->getType() != SI.getType() ||
608 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
611 // If both select arms are non-zero see if we have a select of the form
612 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
613 // for 'x ? 2^n : 0' and fix the thing up at the end.
614 ConstantInt *Offset = 0;
615 if (!TrueVal->isZero() && !FalseVal->isZero()) {
616 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
618 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
623 // Adjust TrueVal and FalseVal to the offset.
624 TrueVal = ConstantInt::get(Builder->getContext(),
625 TrueVal->getValue() - Offset->getValue());
626 FalseVal = ConstantInt::get(Builder->getContext(),
627 FalseVal->getValue() - Offset->getValue());
630 // Make sure the mask in the 'and' and one of the select arms is a power of 2.
631 if (!AndRHS->getValue().isPowerOf2() ||
632 (!TrueVal->getValue().isPowerOf2() &&
633 !FalseVal->getValue().isPowerOf2()))
636 // Determine which shift is needed to transform result of the 'and' into the
638 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
639 unsigned ValZeros = ValC->getValue().logBase2();
640 unsigned AndZeros = AndRHS->getValue().logBase2();
643 if (ValZeros > AndZeros)
644 V = Builder->CreateShl(V, ValZeros - AndZeros);
645 else if (ValZeros < AndZeros)
646 V = Builder->CreateLShr(V, AndZeros - ValZeros);
648 // Okay, now we know that everything is set up, we just don't know whether we
649 // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
650 bool ShouldNotVal = !TrueVal->isZero();
651 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
653 V = Builder->CreateXor(V, ValC);
655 // Apply an offset if needed.
657 V = Builder->CreateAdd(V, Offset);
661 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
662 Value *CondVal = SI.getCondition();
663 Value *TrueVal = SI.getTrueValue();
664 Value *FalseVal = SI.getFalseValue();
666 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
667 return ReplaceInstUsesWith(SI, V);
669 if (SI.getType()->isIntegerTy(1)) {
670 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
671 if (C->getZExtValue()) {
672 // Change: A = select B, true, C --> A = or B, C
673 return BinaryOperator::CreateOr(CondVal, FalseVal);
675 // Change: A = select B, false, C --> A = and !B, C
676 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
677 return BinaryOperator::CreateAnd(NotCond, FalseVal);
678 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
679 if (C->getZExtValue() == false) {
680 // Change: A = select B, C, false --> A = and B, C
681 return BinaryOperator::CreateAnd(CondVal, TrueVal);
683 // Change: A = select B, C, true --> A = or !B, C
684 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
685 return BinaryOperator::CreateOr(NotCond, TrueVal);
688 // select a, b, a -> a&b
689 // select a, a, b -> a|b
690 if (CondVal == TrueVal)
691 return BinaryOperator::CreateOr(CondVal, FalseVal);
692 else if (CondVal == FalseVal)
693 return BinaryOperator::CreateAnd(CondVal, TrueVal);
695 // select a, ~a, b -> (~a)&b
696 // select a, b, ~a -> (~a)|b
697 if (match(TrueVal, m_Not(m_Specific(CondVal))))
698 return BinaryOperator::CreateAnd(TrueVal, FalseVal);
699 else if (match(FalseVal, m_Not(m_Specific(CondVal))))
700 return BinaryOperator::CreateOr(TrueVal, FalseVal);
703 // Selecting between two integer constants?
704 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
705 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
706 // select C, 1, 0 -> zext C to int
707 if (FalseValC->isZero() && TrueValC->getValue() == 1)
708 return new ZExtInst(CondVal, SI.getType());
710 // select C, -1, 0 -> sext C to int
711 if (FalseValC->isZero() && TrueValC->isAllOnesValue())
712 return new SExtInst(CondVal, SI.getType());
714 // select C, 0, 1 -> zext !C to int
715 if (TrueValC->isZero() && FalseValC->getValue() == 1) {
716 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
717 return new ZExtInst(NotCond, SI.getType());
720 // select C, 0, -1 -> sext !C to int
721 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
722 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
723 return new SExtInst(NotCond, SI.getType());
726 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
727 return ReplaceInstUsesWith(SI, V);
730 // See if we are selecting two values based on a comparison of the two values.
731 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
732 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
733 // Transform (X == Y) ? X : Y -> Y
734 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
735 // This is not safe in general for floating point:
736 // consider X== -0, Y== +0.
737 // It becomes safe if either operand is a nonzero constant.
738 ConstantFP *CFPt, *CFPf;
739 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
740 !CFPt->getValueAPF().isZero()) ||
741 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
742 !CFPf->getValueAPF().isZero()))
743 return ReplaceInstUsesWith(SI, FalseVal);
745 // Transform (X une Y) ? X : Y -> X
746 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
747 // This is not safe in general for floating point:
748 // consider X== -0, Y== +0.
749 // It becomes safe if either operand is a nonzero constant.
750 ConstantFP *CFPt, *CFPf;
751 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
752 !CFPt->getValueAPF().isZero()) ||
753 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
754 !CFPf->getValueAPF().isZero()))
755 return ReplaceInstUsesWith(SI, TrueVal);
757 // NOTE: if we wanted to, this is where to detect MIN/MAX
759 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
760 // Transform (X == Y) ? Y : X -> X
761 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
762 // This is not safe in general for floating point:
763 // consider X== -0, Y== +0.
764 // It becomes safe if either operand is a nonzero constant.
765 ConstantFP *CFPt, *CFPf;
766 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
767 !CFPt->getValueAPF().isZero()) ||
768 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
769 !CFPf->getValueAPF().isZero()))
770 return ReplaceInstUsesWith(SI, FalseVal);
772 // Transform (X une Y) ? Y : X -> Y
773 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
774 // This is not safe in general for floating point:
775 // consider X== -0, Y== +0.
776 // It becomes safe if either operand is a nonzero constant.
777 ConstantFP *CFPt, *CFPf;
778 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
779 !CFPt->getValueAPF().isZero()) ||
780 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
781 !CFPf->getValueAPF().isZero()))
782 return ReplaceInstUsesWith(SI, TrueVal);
784 // NOTE: if we wanted to, this is where to detect MIN/MAX
786 // NOTE: if we wanted to, this is where to detect ABS
789 // See if we are selecting two values based on a comparison of the two values.
790 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
791 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
794 if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
795 if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
796 if (TI->hasOneUse() && FI->hasOneUse()) {
797 Instruction *AddOp = 0, *SubOp = 0;
799 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
800 if (TI->getOpcode() == FI->getOpcode())
801 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
804 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
805 // even legal for FP.
806 if ((TI->getOpcode() == Instruction::Sub &&
807 FI->getOpcode() == Instruction::Add) ||
808 (TI->getOpcode() == Instruction::FSub &&
809 FI->getOpcode() == Instruction::FAdd)) {
810 AddOp = FI; SubOp = TI;
811 } else if ((FI->getOpcode() == Instruction::Sub &&
812 TI->getOpcode() == Instruction::Add) ||
813 (FI->getOpcode() == Instruction::FSub &&
814 TI->getOpcode() == Instruction::FAdd)) {
815 AddOp = TI; SubOp = FI;
819 Value *OtherAddOp = 0;
820 if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
821 OtherAddOp = AddOp->getOperand(1);
822 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
823 OtherAddOp = AddOp->getOperand(0);
827 // So at this point we know we have (Y -> OtherAddOp):
828 // select C, (add X, Y), (sub X, Z)
829 Value *NegVal; // Compute -Z
830 if (SI.getType()->isFPOrFPVectorTy()) {
831 NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
833 NegVal = Builder->CreateNeg(SubOp->getOperand(1));
836 Value *NewTrueOp = OtherAddOp;
837 Value *NewFalseOp = NegVal;
839 std::swap(NewTrueOp, NewFalseOp);
841 Builder->CreateSelect(CondVal, NewTrueOp,
842 NewFalseOp, SI.getName() + ".p");
844 if (SI.getType()->isFPOrFPVectorTy())
845 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
847 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
852 // See if we can fold the select into one of our operands.
853 if (SI.getType()->isIntegerTy()) {
854 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
857 // MAX(MAX(a, b), a) -> MAX(a, b)
858 // MIN(MIN(a, b), a) -> MIN(a, b)
859 // MAX(MIN(a, b), a) -> a
860 // MIN(MAX(a, b), a) -> a
861 Value *LHS, *RHS, *LHS2, *RHS2;
862 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
863 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
864 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
867 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
868 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
875 // ABS(ABS(X)) -> ABS(X)
878 // See if we can fold the select into a phi node if the condition is a select.
879 if (isa<PHINode>(SI.getCondition()))
880 // The true/false values have to be live in the PHI predecessor's blocks.
881 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
882 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
883 if (Instruction *NV = FoldOpIntoPhi(SI))
886 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
887 if (TrueSI->getCondition() == CondVal) {
888 if (SI.getTrueValue() == TrueSI->getTrueValue())
890 SI.setOperand(1, TrueSI->getTrueValue());
894 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
895 if (FalseSI->getCondition() == CondVal) {
896 if (SI.getFalseValue() == FalseSI->getFalseValue())
898 SI.setOperand(2, FalseSI->getFalseValue());
903 if (BinaryOperator::isNot(CondVal)) {
904 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
905 SI.setOperand(1, FalseVal);
906 SI.setOperand(2, TrueVal);
910 if (VectorType *VecTy = dyn_cast<VectorType>(SI.getType())) {
911 unsigned VWidth = VecTy->getNumElements();
912 APInt UndefElts(VWidth, 0);
913 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
914 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
916 return ReplaceInstUsesWith(SI, V);
920 if (ConstantVector *CV = dyn_cast<ConstantVector>(CondVal)) {
921 // Form a shufflevector instruction.
922 SmallVector<Constant *, 8> Mask(VWidth);
923 Type *Int32Ty = Type::getInt32Ty(CV->getContext());
924 for (unsigned i = 0; i != VWidth; ++i) {
925 Constant *Elem = cast<Constant>(CV->getOperand(i));
926 if (ConstantInt *E = dyn_cast<ConstantInt>(Elem))
927 Mask[i] = ConstantInt::get(Int32Ty, i + (E->isZero() ? VWidth : 0));
928 else if (isa<UndefValue>(Elem))
929 Mask[i] = UndefValue::get(Int32Ty);
933 Constant *MaskVal = ConstantVector::get(Mask);
934 Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
935 return ReplaceInstUsesWith(SI, V);
938 if (isa<ConstantAggregateZero>(CondVal)) {
939 return ReplaceInstUsesWith(SI, FalseVal);