1 //===- InstCombineSelect.cpp ----------------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the visitSelect function.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "InstCombineInternal.h"
15 #include "llvm/Analysis/ConstantFolding.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/IR/PatternMatch.h"
18 using namespace llvm;
19 using namespace PatternMatch;
20 
21 #define DEBUG_TYPE "instcombine"
22 
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
MatchSelectPattern(Value * V,Value * & LHS,Value * & RHS)27 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
28   SelectInst *SI = dyn_cast<SelectInst>(V);
29   if (!SI) return SPF_UNKNOWN;
30 
31   ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
32   if (!ICI) return SPF_UNKNOWN;
33 
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();
39 
40   LHS = CmpLHS;
41   RHS = CmpRHS;
42 
43   // (icmp X, Y) ? X : Y
44   if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
45     switch (Pred) {
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;
55     }
56   }
57 
58   // (icmp X, Y) ? Y : X
59   if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
60     switch (Pred) {
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;
70     }
71   }
72 
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))))) {
76 
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;
81       }
82 
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;
87       }
88     }
89   }
90 
91   // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)
92 
93   return SPF_UNKNOWN;
94 }
95 
96 
97 /// GetSelectFoldableOperands - We want to turn code that looks like this:
98 ///   %C = or %A, %B
99 ///   %D = select %cond, %C, %A
100 /// into:
101 ///   %C = select %cond, %B, 0
102 ///   %D = or %A, %C
103 ///
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.
107 ///
GetSelectFoldableOperands(Instruction * I)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:
120     return 1;
121   default:
122     return 0;              // Cannot fold
123   }
124 }
125 
126 /// GetSelectFoldableConstant - For the same transformation as the previous
127 /// function, return the identity constant that goes into the select.
GetSelectFoldableConstant(Instruction * I)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);
143   }
144 }
145 
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.
FoldSelectOpOp(SelectInst & SI,Instruction * TI,Instruction * FI)148 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
149                                           Instruction *FI) {
150   if (TI->getNumOperands() == 1) {
151     // If this is a non-volatile load or a cast from the same type,
152     // merge.
153     if (TI->isCast()) {
154       Type *FIOpndTy = FI->getOperand(0)->getType();
155       if (TI->getOperand(0)->getType() != FIOpndTy)
156         return nullptr;
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()))
162         return nullptr;
163     } else {
164       return nullptr;  // unknown unary op.
165     }
166 
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,
171                             TI->getType());
172   }
173 
174   // Only handle binary operators here.
175   if (!isa<BinaryOperator>(TI))
176     return nullptr;
177 
178   // Figure out if the operations have any operands in common.
179   Value *MatchOp, *OtherOpT, *OtherOpF;
180   bool MatchIsOpZero;
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()) {
192     return nullptr;
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;
203   } else {
204     return nullptr;
205   }
206 
207   // If we reach here, they do have operations in common.
208   Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
209                                        OtherOpF, SI.getName()+".v");
210 
211   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
212     if (MatchIsOpZero)
213       return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
214     else
215       return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
216   }
217   llvm_unreachable("Shouldn't get here");
218 }
219 
isSelect01(Constant * C1,Constant * C2)220 static bool isSelect01(Constant *C1, Constant *C2) {
221   ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
222   if (!C1I)
223     return false;
224   ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
225   if (!C2I)
226     return false;
227   if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
228     return false;
229   return C1I->isOne() || C1I->isAllOnesValue() ||
230          C2I->isOne() || C2I->isAllOnesValue();
231 }
232 
233 /// FoldSelectIntoOp - Try fold the select into one of the operands to
234 /// facilitate further optimization.
FoldSelectIntoOp(SelectInst & SI,Value * TrueVal,Value * FalseVal)235 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
236                                             Value *FalseVal) {
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)) {
245           OpToFold = 1;
246         } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
247           OpToFold = 2;
248         }
249 
250         if (OpToFold) {
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(),
260                                                         FalseVal, NewSel);
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());
266             }
267             return BO;
268           }
269         }
270       }
271     }
272   }
273 
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)) {
280           OpToFold = 1;
281         } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
282           OpToFold = 2;
283         }
284 
285         if (OpToFold) {
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(),
295                                                         TrueVal, NewSel);
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());
301             }
302             return BO;
303           }
304         }
305       }
306     }
307   }
308 
309   return nullptr;
310 }
311 
312 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
313 /// replaced with RepOp.
SimplifyWithOpReplaced(Value * V,Value * Op,Value * RepOp,const TargetLibraryInfo * TLI,const DataLayout & DL,DominatorTree * DT,AssumptionCache * AC)314 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
315                                      const TargetLibraryInfo *TLI,
316                                      const DataLayout &DL, DominatorTree *DT,
317                                      AssumptionCache *AC) {
318   // Trivial replacement.
319   if (V == Op)
320     return RepOp;
321 
322   Instruction *I = dyn_cast<Instruction>(V);
323   if (!I)
324     return nullptr;
325 
326   // If this is a binary operator, try to simplify it with the replaced op.
327   if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
328     if (B->getOperand(0) == Op)
329       return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
330     if (B->getOperand(1) == Op)
331       return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
332   }
333 
334   // Same for CmpInsts.
335   if (CmpInst *C = dyn_cast<CmpInst>(I)) {
336     if (C->getOperand(0) == Op)
337       return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), DL,
338                              TLI, DT, AC);
339     if (C->getOperand(1) == Op)
340       return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, DL,
341                              TLI, DT, AC);
342   }
343 
344   // TODO: We could hand off more cases to instsimplify here.
345 
346   // If all operands are constant after substituting Op for RepOp then we can
347   // constant fold the instruction.
348   if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
349     // Build a list of all constant operands.
350     SmallVector<Constant*, 8> ConstOps;
351     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
352       if (I->getOperand(i) == Op)
353         ConstOps.push_back(CRepOp);
354       else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
355         ConstOps.push_back(COp);
356       else
357         break;
358     }
359 
360     // All operands were constants, fold it.
361     if (ConstOps.size() == I->getNumOperands()) {
362       if (CmpInst *C = dyn_cast<CmpInst>(I))
363         return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
364                                                ConstOps[1], DL, TLI);
365 
366       if (LoadInst *LI = dyn_cast<LoadInst>(I))
367         if (!LI->isVolatile())
368           return ConstantFoldLoadFromConstPtr(ConstOps[0], DL);
369 
370       return ConstantFoldInstOperands(I->getOpcode(), I->getType(), ConstOps,
371                                       DL, TLI);
372     }
373   }
374 
375   return nullptr;
376 }
377 
378 /// foldSelectICmpAndOr - We want to turn:
379 ///   (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
380 /// into:
381 ///   (or (shl (and X, C1), C3), y)
382 /// iff:
383 ///   C1 and C2 are both powers of 2
384 /// where:
385 ///   C3 = Log(C2) - Log(C1)
386 ///
387 /// This transform handles cases where:
388 /// 1. The icmp predicate is inverted
389 /// 2. The select operands are reversed
390 /// 3. The magnitude of C2 and C1 are flipped
foldSelectICmpAndOr(const SelectInst & SI,Value * TrueVal,Value * FalseVal,InstCombiner::BuilderTy * Builder)391 static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
392                                   Value *FalseVal,
393                                   InstCombiner::BuilderTy *Builder) {
394   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
395   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
396     return nullptr;
397 
398   Value *CmpLHS = IC->getOperand(0);
399   Value *CmpRHS = IC->getOperand(1);
400 
401   if (!match(CmpRHS, m_Zero()))
402     return nullptr;
403 
404   Value *X;
405   const APInt *C1;
406   if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
407     return nullptr;
408 
409   const APInt *C2;
410   bool OrOnTrueVal = false;
411   bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
412   if (!OrOnFalseVal)
413     OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
414 
415   if (!OrOnFalseVal && !OrOnTrueVal)
416     return nullptr;
417 
418   Value *V = CmpLHS;
419   Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
420 
421   unsigned C1Log = C1->logBase2();
422   unsigned C2Log = C2->logBase2();
423   if (C2Log > C1Log) {
424     V = Builder->CreateZExtOrTrunc(V, Y->getType());
425     V = Builder->CreateShl(V, C2Log - C1Log);
426   } else if (C1Log > C2Log) {
427     V = Builder->CreateLShr(V, C1Log - C2Log);
428     V = Builder->CreateZExtOrTrunc(V, Y->getType());
429   } else
430     V = Builder->CreateZExtOrTrunc(V, Y->getType());
431 
432   ICmpInst::Predicate Pred = IC->getPredicate();
433   if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
434       (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
435     V = Builder->CreateXor(V, *C2);
436 
437   return Builder->CreateOr(V, Y);
438 }
439 
440 /// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
441 /// call to cttz/ctlz with flag 'is_zero_undef' cleared.
442 ///
443 /// For example, we can fold the following code sequence:
444 /// \code
445 ///   %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
446 ///   %1 = icmp ne i32 %x, 0
447 ///   %2 = select i1 %1, i32 %0, i32 32
448 /// \code
449 ///
450 /// into:
451 ///   %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
foldSelectCttzCtlz(ICmpInst * ICI,Value * TrueVal,Value * FalseVal,InstCombiner::BuilderTy * Builder)452 static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
453                                   InstCombiner::BuilderTy *Builder) {
454   ICmpInst::Predicate Pred = ICI->getPredicate();
455   Value *CmpLHS = ICI->getOperand(0);
456   Value *CmpRHS = ICI->getOperand(1);
457 
458   // Check if the condition value compares a value for equality against zero.
459   if (!ICI->isEquality() || !match(CmpRHS, m_Zero()))
460     return nullptr;
461 
462   Value *Count = FalseVal;
463   Value *ValueOnZero = TrueVal;
464   if (Pred == ICmpInst::ICMP_NE)
465     std::swap(Count, ValueOnZero);
466 
467   // Skip zero extend/truncate.
468   Value *V = nullptr;
469   if (match(Count, m_ZExt(m_Value(V))) ||
470       match(Count, m_Trunc(m_Value(V))))
471     Count = V;
472 
473   // Check if the value propagated on zero is a constant number equal to the
474   // sizeof in bits of 'Count'.
475   unsigned SizeOfInBits = Count->getType()->getScalarSizeInBits();
476   if (!match(ValueOnZero, m_SpecificInt(SizeOfInBits)))
477     return nullptr;
478 
479   // Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the
480   // input to the cttz/ctlz is used as LHS for the compare instruction.
481   if (match(Count, m_Intrinsic<Intrinsic::cttz>(m_Specific(CmpLHS))) ||
482       match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS)))) {
483     IntrinsicInst *II = cast<IntrinsicInst>(Count);
484     IRBuilder<> Builder(II);
485     // Explicitly clear the 'undef_on_zero' flag.
486     IntrinsicInst *NewI = cast<IntrinsicInst>(II->clone());
487     Type *Ty = NewI->getArgOperand(1)->getType();
488     NewI->setArgOperand(1, Constant::getNullValue(Ty));
489     Builder.Insert(NewI);
490     return Builder.CreateZExtOrTrunc(NewI, ValueOnZero->getType());
491   }
492 
493   return nullptr;
494 }
495 
496 /// visitSelectInstWithICmp - Visit a SelectInst that has an
497 /// ICmpInst as its first operand.
498 ///
visitSelectInstWithICmp(SelectInst & SI,ICmpInst * ICI)499 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
500                                                    ICmpInst *ICI) {
501   bool Changed = false;
502   ICmpInst::Predicate Pred = ICI->getPredicate();
503   Value *CmpLHS = ICI->getOperand(0);
504   Value *CmpRHS = ICI->getOperand(1);
505   Value *TrueVal = SI.getTrueValue();
506   Value *FalseVal = SI.getFalseValue();
507 
508   // Check cases where the comparison is with a constant that
509   // can be adjusted to fit the min/max idiom. We may move or edit ICI
510   // here, so make sure the select is the only user.
511   if (ICI->hasOneUse())
512     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
513       // X < MIN ? T : F  -->  F
514       if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
515           && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
516         return ReplaceInstUsesWith(SI, FalseVal);
517       // X > MAX ? T : F  -->  F
518       else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
519                && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
520         return ReplaceInstUsesWith(SI, FalseVal);
521       switch (Pred) {
522       default: break;
523       case ICmpInst::ICMP_ULT:
524       case ICmpInst::ICMP_SLT:
525       case ICmpInst::ICMP_UGT:
526       case ICmpInst::ICMP_SGT: {
527         // These transformations only work for selects over integers.
528         IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
529         if (!SelectTy)
530           break;
531 
532         Constant *AdjustedRHS;
533         if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
534           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
535         else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
536           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
537 
538         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
539         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
540         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
541             (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
542           ; // Nothing to do here. Values match without any sign/zero extension.
543 
544         // Types do not match. Instead of calculating this with mixed types
545         // promote all to the larger type. This enables scalar evolution to
546         // analyze this expression.
547         else if (CmpRHS->getType()->getScalarSizeInBits()
548                  < SelectTy->getBitWidth()) {
549           Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
550 
551           // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
552           // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
553           // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
554           // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
555           if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
556                 sextRHS == FalseVal) {
557             CmpLHS = TrueVal;
558             AdjustedRHS = sextRHS;
559           } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
560                      sextRHS == TrueVal) {
561             CmpLHS = FalseVal;
562             AdjustedRHS = sextRHS;
563           } else if (ICI->isUnsigned()) {
564             Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
565             // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
566             // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
567             // zext + signed compare cannot be changed:
568             //    0xff <s 0x00, but 0x00ff >s 0x0000
569             if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
570                 zextRHS == FalseVal) {
571               CmpLHS = TrueVal;
572               AdjustedRHS = zextRHS;
573             } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
574                        zextRHS == TrueVal) {
575               CmpLHS = FalseVal;
576               AdjustedRHS = zextRHS;
577             } else
578               break;
579           } else
580             break;
581         } else
582           break;
583 
584         Pred = ICmpInst::getSwappedPredicate(Pred);
585         CmpRHS = AdjustedRHS;
586         std::swap(FalseVal, TrueVal);
587         ICI->setPredicate(Pred);
588         ICI->setOperand(0, CmpLHS);
589         ICI->setOperand(1, CmpRHS);
590         SI.setOperand(1, TrueVal);
591         SI.setOperand(2, FalseVal);
592 
593         // Move ICI instruction right before the select instruction. Otherwise
594         // the sext/zext value may be defined after the ICI instruction uses it.
595         ICI->moveBefore(&SI);
596 
597         Changed = true;
598         break;
599       }
600       }
601     }
602 
603   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
604   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
605   // FIXME: Type and constness constraints could be lifted, but we have to
606   //        watch code size carefully. We should consider xor instead of
607   //        sub/add when we decide to do that.
608   if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
609     if (TrueVal->getType() == Ty) {
610       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
611         ConstantInt *C1 = nullptr, *C2 = nullptr;
612         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
613           C1 = dyn_cast<ConstantInt>(TrueVal);
614           C2 = dyn_cast<ConstantInt>(FalseVal);
615         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
616           C1 = dyn_cast<ConstantInt>(FalseVal);
617           C2 = dyn_cast<ConstantInt>(TrueVal);
618         }
619         if (C1 && C2) {
620           // This shift results in either -1 or 0.
621           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
622 
623           // Check if we can express the operation with a single or.
624           if (C2->isAllOnesValue())
625             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
626 
627           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
628           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
629         }
630       }
631     }
632   }
633 
634   // If we have an equality comparison then we know the value in one of the
635   // arms of the select. See if substituting this value into the arm and
636   // simplifying the result yields the same value as the other arm.
637   if (Pred == ICmpInst::ICMP_EQ) {
638     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
639             TrueVal ||
640         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
641             TrueVal)
642       return ReplaceInstUsesWith(SI, FalseVal);
643     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
644             FalseVal ||
645         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
646             FalseVal)
647       return ReplaceInstUsesWith(SI, FalseVal);
648   } else if (Pred == ICmpInst::ICMP_NE) {
649     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
650             FalseVal ||
651         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
652             FalseVal)
653       return ReplaceInstUsesWith(SI, TrueVal);
654     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TLI, DL, DT, AC) ==
655             TrueVal ||
656         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TLI, DL, DT, AC) ==
657             TrueVal)
658       return ReplaceInstUsesWith(SI, TrueVal);
659   }
660 
661   // NOTE: if we wanted to, this is where to detect integer MIN/MAX
662 
663   if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
664     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
665       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
666       SI.setOperand(1, CmpRHS);
667       Changed = true;
668     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
669       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
670       SI.setOperand(2, CmpRHS);
671       Changed = true;
672     }
673   }
674 
675   if (unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits()) {
676     APInt MinSignedValue = APInt::getSignBit(BitWidth);
677     Value *X;
678     const APInt *Y, *C;
679     bool TrueWhenUnset;
680     bool IsBitTest = false;
681     if (ICmpInst::isEquality(Pred) &&
682         match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
683         match(CmpRHS, m_Zero())) {
684       IsBitTest = true;
685       TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
686     } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
687       X = CmpLHS;
688       Y = &MinSignedValue;
689       IsBitTest = true;
690       TrueWhenUnset = false;
691     } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
692       X = CmpLHS;
693       Y = &MinSignedValue;
694       IsBitTest = true;
695       TrueWhenUnset = true;
696     }
697     if (IsBitTest) {
698       Value *V = nullptr;
699       // (X & Y) == 0 ? X : X ^ Y  --> X & ~Y
700       if (TrueWhenUnset && TrueVal == X &&
701           match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
702         V = Builder->CreateAnd(X, ~(*Y));
703       // (X & Y) != 0 ? X ^ Y : X  --> X & ~Y
704       else if (!TrueWhenUnset && FalseVal == X &&
705                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
706         V = Builder->CreateAnd(X, ~(*Y));
707       // (X & Y) == 0 ? X ^ Y : X  --> X | Y
708       else if (TrueWhenUnset && FalseVal == X &&
709                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
710         V = Builder->CreateOr(X, *Y);
711       // (X & Y) != 0 ? X : X ^ Y  --> X | Y
712       else if (!TrueWhenUnset && TrueVal == X &&
713                match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
714         V = Builder->CreateOr(X, *Y);
715 
716       if (V)
717         return ReplaceInstUsesWith(SI, V);
718     }
719   }
720 
721   if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
722     return ReplaceInstUsesWith(SI, V);
723 
724   if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder))
725     return ReplaceInstUsesWith(SI, V);
726 
727   return Changed ? &SI : nullptr;
728 }
729 
730 
731 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
732 /// PHI node (but the two may be in different blocks).  See if the true/false
733 /// values (V) are live in all of the predecessor blocks of the PHI.  For
734 /// example, cases like this cannot be mapped:
735 ///
736 ///   X = phi [ C1, BB1], [C2, BB2]
737 ///   Y = add
738 ///   Z = select X, Y, 0
739 ///
740 /// because Y is not live in BB1/BB2.
741 ///
CanSelectOperandBeMappingIntoPredBlock(const Value * V,const SelectInst & SI)742 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
743                                                    const SelectInst &SI) {
744   // If the value is a non-instruction value like a constant or argument, it
745   // can always be mapped.
746   const Instruction *I = dyn_cast<Instruction>(V);
747   if (!I) return true;
748 
749   // If V is a PHI node defined in the same block as the condition PHI, we can
750   // map the arguments.
751   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
752 
753   if (const PHINode *VP = dyn_cast<PHINode>(I))
754     if (VP->getParent() == CondPHI->getParent())
755       return true;
756 
757   // Otherwise, if the PHI and select are defined in the same block and if V is
758   // defined in a different block, then we can transform it.
759   if (SI.getParent() == CondPHI->getParent() &&
760       I->getParent() != CondPHI->getParent())
761     return true;
762 
763   // Otherwise we have a 'hard' case and we can't tell without doing more
764   // detailed dominator based analysis, punt.
765   return false;
766 }
767 
768 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
769 ///   SPF2(SPF1(A, B), C)
FoldSPFofSPF(Instruction * Inner,SelectPatternFlavor SPF1,Value * A,Value * B,Instruction & Outer,SelectPatternFlavor SPF2,Value * C)770 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
771                                         SelectPatternFlavor SPF1,
772                                         Value *A, Value *B,
773                                         Instruction &Outer,
774                                         SelectPatternFlavor SPF2, Value *C) {
775   if (C == A || C == B) {
776     // MAX(MAX(A, B), B) -> MAX(A, B)
777     // MIN(MIN(a, b), a) -> MIN(a, b)
778     if (SPF1 == SPF2)
779       return ReplaceInstUsesWith(Outer, Inner);
780 
781     // MAX(MIN(a, b), a) -> a
782     // MIN(MAX(a, b), a) -> a
783     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
784         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
785         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
786         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
787       return ReplaceInstUsesWith(Outer, C);
788   }
789 
790   if (SPF1 == SPF2) {
791     if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
792       if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
793         APInt ACB = CB->getValue();
794         APInt ACC = CC->getValue();
795 
796         // MIN(MIN(A, 23), 97) -> MIN(A, 23)
797         // MAX(MAX(A, 97), 23) -> MAX(A, 97)
798         if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
799             (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
800             (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
801             (SPF1 == SPF_SMAX && ACB.sge(ACC)))
802           return ReplaceInstUsesWith(Outer, Inner);
803 
804         // MIN(MIN(A, 97), 23) -> MIN(A, 23)
805         // MAX(MAX(A, 23), 97) -> MAX(A, 97)
806         if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
807             (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
808             (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
809             (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
810           Outer.replaceUsesOfWith(Inner, A);
811           return &Outer;
812         }
813       }
814     }
815   }
816 
817   // ABS(ABS(X)) -> ABS(X)
818   // NABS(NABS(X)) -> NABS(X)
819   if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
820     return ReplaceInstUsesWith(Outer, Inner);
821   }
822 
823   // ABS(NABS(X)) -> ABS(X)
824   // NABS(ABS(X)) -> NABS(X)
825   if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
826       (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
827     SelectInst *SI = cast<SelectInst>(Inner);
828     Value *NewSI = Builder->CreateSelect(
829         SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
830     return ReplaceInstUsesWith(Outer, NewSI);
831   }
832   return nullptr;
833 }
834 
835 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
836 /// both be) and we have an icmp instruction with zero, and we have an 'and'
837 /// with the non-constant value and a power of two we can turn the select
838 /// into a shift on the result of the 'and'.
foldSelectICmpAnd(const SelectInst & SI,ConstantInt * TrueVal,ConstantInt * FalseVal,InstCombiner::BuilderTy * Builder)839 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
840                                 ConstantInt *FalseVal,
841                                 InstCombiner::BuilderTy *Builder) {
842   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
843   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
844     return nullptr;
845 
846   if (!match(IC->getOperand(1), m_Zero()))
847     return nullptr;
848 
849   ConstantInt *AndRHS;
850   Value *LHS = IC->getOperand(0);
851   if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
852     return nullptr;
853 
854   // If both select arms are non-zero see if we have a select of the form
855   // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
856   // for 'x ? 2^n : 0' and fix the thing up at the end.
857   ConstantInt *Offset = nullptr;
858   if (!TrueVal->isZero() && !FalseVal->isZero()) {
859     if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
860       Offset = FalseVal;
861     else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
862       Offset = TrueVal;
863     else
864       return nullptr;
865 
866     // Adjust TrueVal and FalseVal to the offset.
867     TrueVal = ConstantInt::get(Builder->getContext(),
868                                TrueVal->getValue() - Offset->getValue());
869     FalseVal = ConstantInt::get(Builder->getContext(),
870                                 FalseVal->getValue() - Offset->getValue());
871   }
872 
873   // Make sure the mask in the 'and' and one of the select arms is a power of 2.
874   if (!AndRHS->getValue().isPowerOf2() ||
875       (!TrueVal->getValue().isPowerOf2() &&
876        !FalseVal->getValue().isPowerOf2()))
877     return nullptr;
878 
879   // Determine which shift is needed to transform result of the 'and' into the
880   // desired result.
881   ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
882   unsigned ValZeros = ValC->getValue().logBase2();
883   unsigned AndZeros = AndRHS->getValue().logBase2();
884 
885   // If types don't match we can still convert the select by introducing a zext
886   // or a trunc of the 'and'. The trunc case requires that all of the truncated
887   // bits are zero, we can figure that out by looking at the 'and' mask.
888   if (AndZeros >= ValC->getBitWidth())
889     return nullptr;
890 
891   Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
892   if (ValZeros > AndZeros)
893     V = Builder->CreateShl(V, ValZeros - AndZeros);
894   else if (ValZeros < AndZeros)
895     V = Builder->CreateLShr(V, AndZeros - ValZeros);
896 
897   // Okay, now we know that everything is set up, we just don't know whether we
898   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
899   bool ShouldNotVal = !TrueVal->isZero();
900   ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
901   if (ShouldNotVal)
902     V = Builder->CreateXor(V, ValC);
903 
904   // Apply an offset if needed.
905   if (Offset)
906     V = Builder->CreateAdd(V, Offset);
907   return V;
908 }
909 
visitSelectInst(SelectInst & SI)910 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
911   Value *CondVal = SI.getCondition();
912   Value *TrueVal = SI.getTrueValue();
913   Value *FalseVal = SI.getFalseValue();
914 
915   if (Value *V =
916           SimplifySelectInst(CondVal, TrueVal, FalseVal, DL, TLI, DT, AC))
917     return ReplaceInstUsesWith(SI, V);
918 
919   if (SI.getType()->isIntegerTy(1)) {
920     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
921       if (C->getZExtValue()) {
922         // Change: A = select B, true, C --> A = or B, C
923         return BinaryOperator::CreateOr(CondVal, FalseVal);
924       }
925       // Change: A = select B, false, C --> A = and !B, C
926       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
927       return BinaryOperator::CreateAnd(NotCond, FalseVal);
928     }
929     if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
930       if (!C->getZExtValue()) {
931         // Change: A = select B, C, false --> A = and B, C
932         return BinaryOperator::CreateAnd(CondVal, TrueVal);
933       }
934       // Change: A = select B, C, true --> A = or !B, C
935       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
936       return BinaryOperator::CreateOr(NotCond, TrueVal);
937     }
938 
939     // select a, b, a  -> a&b
940     // select a, a, b  -> a|b
941     if (CondVal == TrueVal)
942       return BinaryOperator::CreateOr(CondVal, FalseVal);
943     if (CondVal == FalseVal)
944       return BinaryOperator::CreateAnd(CondVal, TrueVal);
945 
946     // select a, ~a, b -> (~a)&b
947     // select a, b, ~a -> (~a)|b
948     if (match(TrueVal, m_Not(m_Specific(CondVal))))
949       return BinaryOperator::CreateAnd(TrueVal, FalseVal);
950     if (match(FalseVal, m_Not(m_Specific(CondVal))))
951       return BinaryOperator::CreateOr(TrueVal, FalseVal);
952   }
953 
954   // Selecting between two integer constants?
955   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
956     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
957       // select C, 1, 0 -> zext C to int
958       if (FalseValC->isZero() && TrueValC->getValue() == 1)
959         return new ZExtInst(CondVal, SI.getType());
960 
961       // select C, -1, 0 -> sext C to int
962       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
963         return new SExtInst(CondVal, SI.getType());
964 
965       // select C, 0, 1 -> zext !C to int
966       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
967         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
968         return new ZExtInst(NotCond, SI.getType());
969       }
970 
971       // select C, 0, -1 -> sext !C to int
972       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
973         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
974         return new SExtInst(NotCond, SI.getType());
975       }
976 
977       if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
978         return ReplaceInstUsesWith(SI, V);
979     }
980 
981   // See if we are selecting two values based on a comparison of the two values.
982   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
983     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
984       // Transform (X == Y) ? X : Y  -> Y
985       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
986         // This is not safe in general for floating point:
987         // consider X== -0, Y== +0.
988         // It becomes safe if either operand is a nonzero constant.
989         ConstantFP *CFPt, *CFPf;
990         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
991               !CFPt->getValueAPF().isZero()) ||
992             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
993              !CFPf->getValueAPF().isZero()))
994         return ReplaceInstUsesWith(SI, FalseVal);
995       }
996       // Transform (X une Y) ? X : Y  -> X
997       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
998         // This is not safe in general for floating point:
999         // consider X== -0, Y== +0.
1000         // It becomes safe if either operand is a nonzero constant.
1001         ConstantFP *CFPt, *CFPf;
1002         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1003               !CFPt->getValueAPF().isZero()) ||
1004             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1005              !CFPf->getValueAPF().isZero()))
1006         return ReplaceInstUsesWith(SI, TrueVal);
1007       }
1008 
1009       // Canonicalize to use ordered comparisons by swapping the select
1010       // operands.
1011       //
1012       // e.g.
1013       // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
1014       if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
1015         FCmpInst::Predicate InvPred = FCI->getInversePredicate();
1016         Value *NewCond = Builder->CreateFCmp(InvPred, TrueVal, FalseVal,
1017                                              FCI->getName() + ".inv");
1018 
1019         return SelectInst::Create(NewCond, FalseVal, TrueVal,
1020                                   SI.getName() + ".p");
1021       }
1022 
1023       // NOTE: if we wanted to, this is where to detect MIN/MAX
1024     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
1025       // Transform (X == Y) ? Y : X  -> X
1026       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
1027         // This is not safe in general for floating point:
1028         // consider X== -0, Y== +0.
1029         // It becomes safe if either operand is a nonzero constant.
1030         ConstantFP *CFPt, *CFPf;
1031         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1032               !CFPt->getValueAPF().isZero()) ||
1033             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1034              !CFPf->getValueAPF().isZero()))
1035           return ReplaceInstUsesWith(SI, FalseVal);
1036       }
1037       // Transform (X une Y) ? Y : X  -> Y
1038       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
1039         // This is not safe in general for floating point:
1040         // consider X== -0, Y== +0.
1041         // It becomes safe if either operand is a nonzero constant.
1042         ConstantFP *CFPt, *CFPf;
1043         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
1044               !CFPt->getValueAPF().isZero()) ||
1045             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
1046              !CFPf->getValueAPF().isZero()))
1047           return ReplaceInstUsesWith(SI, TrueVal);
1048       }
1049 
1050       // Canonicalize to use ordered comparisons by swapping the select
1051       // operands.
1052       //
1053       // e.g.
1054       // (X ugt Y) ? X : Y -> (X ole Y) ? X : Y
1055       if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
1056         FCmpInst::Predicate InvPred = FCI->getInversePredicate();
1057         Value *NewCond = Builder->CreateFCmp(InvPred, FalseVal, TrueVal,
1058                                              FCI->getName() + ".inv");
1059 
1060         return SelectInst::Create(NewCond, FalseVal, TrueVal,
1061                                   SI.getName() + ".p");
1062       }
1063 
1064       // NOTE: if we wanted to, this is where to detect MIN/MAX
1065     }
1066     // NOTE: if we wanted to, this is where to detect ABS
1067   }
1068 
1069   // See if we are selecting two values based on a comparison of the two values.
1070   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
1071     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
1072       return Result;
1073 
1074   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
1075     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
1076       if (TI->hasOneUse() && FI->hasOneUse()) {
1077         Instruction *AddOp = nullptr, *SubOp = nullptr;
1078 
1079         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
1080         if (TI->getOpcode() == FI->getOpcode())
1081           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
1082             return IV;
1083 
1084         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
1085         // even legal for FP.
1086         if ((TI->getOpcode() == Instruction::Sub &&
1087              FI->getOpcode() == Instruction::Add) ||
1088             (TI->getOpcode() == Instruction::FSub &&
1089              FI->getOpcode() == Instruction::FAdd)) {
1090           AddOp = FI; SubOp = TI;
1091         } else if ((FI->getOpcode() == Instruction::Sub &&
1092                     TI->getOpcode() == Instruction::Add) ||
1093                    (FI->getOpcode() == Instruction::FSub &&
1094                     TI->getOpcode() == Instruction::FAdd)) {
1095           AddOp = TI; SubOp = FI;
1096         }
1097 
1098         if (AddOp) {
1099           Value *OtherAddOp = nullptr;
1100           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
1101             OtherAddOp = AddOp->getOperand(1);
1102           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
1103             OtherAddOp = AddOp->getOperand(0);
1104           }
1105 
1106           if (OtherAddOp) {
1107             // So at this point we know we have (Y -> OtherAddOp):
1108             //        select C, (add X, Y), (sub X, Z)
1109             Value *NegVal;  // Compute -Z
1110             if (SI.getType()->isFPOrFPVectorTy()) {
1111               NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
1112               if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
1113                 FastMathFlags Flags = AddOp->getFastMathFlags();
1114                 Flags &= SubOp->getFastMathFlags();
1115                 NegInst->setFastMathFlags(Flags);
1116               }
1117             } else {
1118               NegVal = Builder->CreateNeg(SubOp->getOperand(1));
1119             }
1120 
1121             Value *NewTrueOp = OtherAddOp;
1122             Value *NewFalseOp = NegVal;
1123             if (AddOp != TI)
1124               std::swap(NewTrueOp, NewFalseOp);
1125             Value *NewSel =
1126               Builder->CreateSelect(CondVal, NewTrueOp,
1127                                     NewFalseOp, SI.getName() + ".p");
1128 
1129             if (SI.getType()->isFPOrFPVectorTy()) {
1130               Instruction *RI =
1131                 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
1132 
1133               FastMathFlags Flags = AddOp->getFastMathFlags();
1134               Flags &= SubOp->getFastMathFlags();
1135               RI->setFastMathFlags(Flags);
1136               return RI;
1137             } else
1138               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
1139           }
1140         }
1141       }
1142 
1143   // See if we can fold the select into one of our operands.
1144   if (SI.getType()->isIntegerTy()) {
1145     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
1146       return FoldI;
1147 
1148     Value *LHS, *RHS, *LHS2, *RHS2;
1149     SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS);
1150 
1151     // MAX(MAX(a, b), a) -> MAX(a, b)
1152     // MIN(MIN(a, b), a) -> MIN(a, b)
1153     // MAX(MIN(a, b), a) -> a
1154     // MIN(MAX(a, b), a) -> a
1155     if (SPF) {
1156       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
1157         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
1158                                           SI, SPF, RHS))
1159           return R;
1160       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
1161         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
1162                                           SI, SPF, LHS))
1163           return R;
1164     }
1165 
1166     // MAX(~a, ~b) -> ~MIN(a, b)
1167     if (SPF == SPF_SMAX || SPF == SPF_UMAX) {
1168       if (IsFreeToInvert(LHS, LHS->hasNUses(2)) &&
1169           IsFreeToInvert(RHS, RHS->hasNUses(2))) {
1170 
1171         // This transform adds a xor operation and that extra cost needs to be
1172         // justified.  We look for simplifications that will result from
1173         // applying this rule:
1174 
1175         bool Profitable =
1176             (LHS->hasNUses(2) && match(LHS, m_Not(m_Value()))) ||
1177             (RHS->hasNUses(2) && match(RHS, m_Not(m_Value()))) ||
1178             (SI.hasOneUse() && match(*SI.user_begin(), m_Not(m_Value())));
1179 
1180         if (Profitable) {
1181           Value *NewLHS = Builder->CreateNot(LHS);
1182           Value *NewRHS = Builder->CreateNot(RHS);
1183           Value *NewCmp = SPF == SPF_SMAX
1184                               ? Builder->CreateICmpSLT(NewLHS, NewRHS)
1185                               : Builder->CreateICmpULT(NewLHS, NewRHS);
1186           Value *NewSI =
1187               Builder->CreateNot(Builder->CreateSelect(NewCmp, NewLHS, NewRHS));
1188           return ReplaceInstUsesWith(SI, NewSI);
1189         }
1190       }
1191     }
1192 
1193     // TODO.
1194     // ABS(-X) -> ABS(X)
1195   }
1196 
1197   // See if we can fold the select into a phi node if the condition is a select.
1198   if (isa<PHINode>(SI.getCondition()))
1199     // The true/false values have to be live in the PHI predecessor's blocks.
1200     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
1201         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
1202       if (Instruction *NV = FoldOpIntoPhi(SI))
1203         return NV;
1204 
1205   if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
1206     if (TrueSI->getCondition()->getType() == CondVal->getType()) {
1207       // select(C, select(C, a, b), c) -> select(C, a, c)
1208       if (TrueSI->getCondition() == CondVal) {
1209         if (SI.getTrueValue() == TrueSI->getTrueValue())
1210           return nullptr;
1211         SI.setOperand(1, TrueSI->getTrueValue());
1212         return &SI;
1213       }
1214       // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
1215       // We choose this as normal form to enable folding on the And and shortening
1216       // paths for the values (this helps GetUnderlyingObjects() for example).
1217       if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
1218         Value *And = Builder->CreateAnd(CondVal, TrueSI->getCondition());
1219         SI.setOperand(0, And);
1220         SI.setOperand(1, TrueSI->getTrueValue());
1221         return &SI;
1222       }
1223     }
1224   }
1225   if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
1226     if (FalseSI->getCondition()->getType() == CondVal->getType()) {
1227       // select(C, a, select(C, b, c)) -> select(C, a, c)
1228       if (FalseSI->getCondition() == CondVal) {
1229         if (SI.getFalseValue() == FalseSI->getFalseValue())
1230           return nullptr;
1231         SI.setOperand(2, FalseSI->getFalseValue());
1232         return &SI;
1233       }
1234       // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
1235       if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
1236         Value *Or = Builder->CreateOr(CondVal, FalseSI->getCondition());
1237         SI.setOperand(0, Or);
1238         SI.setOperand(2, FalseSI->getFalseValue());
1239         return &SI;
1240       }
1241     }
1242   }
1243 
1244   if (BinaryOperator::isNot(CondVal)) {
1245     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
1246     SI.setOperand(1, FalseVal);
1247     SI.setOperand(2, TrueVal);
1248     return &SI;
1249   }
1250 
1251   if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
1252     unsigned VWidth = VecTy->getNumElements();
1253     APInt UndefElts(VWidth, 0);
1254     APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
1255     if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
1256       if (V != &SI)
1257         return ReplaceInstUsesWith(SI, V);
1258       return &SI;
1259     }
1260 
1261     if (isa<ConstantAggregateZero>(CondVal)) {
1262       return ReplaceInstUsesWith(SI, FalseVal);
1263     }
1264   }
1265 
1266   return nullptr;
1267 }
1268