1 //===- InstructionCombining.cpp - Combine multiple instructions -----------===//
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 // InstructionCombining - Combine instructions to form fewer, simple
11 // instructions. This pass does not modify the CFG. This pass is where
12 // algebraic simplification happens.
14 // This pass combines things like:
20 // This is a simple worklist driven algorithm.
22 // This pass guarantees that the following canonicalizations are performed on
24 // 1. If a binary operator has a constant operand, it is moved to the RHS
25 // 2. Bitwise operators with constant operands are always grouped so that
26 // shifts are performed first, then or's, then and's, then xor's.
27 // 3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible
28 // 4. All cmp instructions on boolean values are replaced with logical ops
29 // 5. add X, X is represented as (X*2) => (X << 1)
30 // 6. Multiplies with a power-of-two constant argument are transformed into
34 //===----------------------------------------------------------------------===//
36 #define DEBUG_TYPE "instcombine"
37 #include "llvm/Transforms/Scalar.h"
38 #include "InstCombine.h"
39 #include "llvm/IntrinsicInst.h"
40 #include "llvm/Analysis/ConstantFolding.h"
41 #include "llvm/Analysis/InstructionSimplify.h"
42 #include "llvm/Analysis/MemoryBuiltins.h"
43 #include "llvm/Target/TargetData.h"
44 #include "llvm/Transforms/Utils/Local.h"
45 #include "llvm/Support/CFG.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/GetElementPtrTypeIterator.h"
48 #include "llvm/Support/PatternMatch.h"
49 #include "llvm/ADT/SmallPtrSet.h"
50 #include "llvm/ADT/Statistic.h"
54 using namespace llvm::PatternMatch;
56 STATISTIC(NumCombined , "Number of insts combined");
57 STATISTIC(NumConstProp, "Number of constant folds");
58 STATISTIC(NumDeadInst , "Number of dead inst eliminated");
59 STATISTIC(NumSunkInst , "Number of instructions sunk");
62 char InstCombiner::ID = 0;
63 static RegisterPass<InstCombiner>
64 X("instcombine", "Combine redundant instructions");
66 void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
67 AU.addPreservedID(LCSSAID);
72 /// ShouldChangeType - Return true if it is desirable to convert a computation
73 /// from 'From' to 'To'. We don't want to convert from a legal to an illegal
74 /// type for example, or from a smaller to a larger illegal type.
75 bool InstCombiner::ShouldChangeType(const Type *From, const Type *To) const {
76 assert(From->isIntegerTy() && To->isIntegerTy());
78 // If we don't have TD, we don't know if the source/dest are legal.
79 if (!TD) return false;
81 unsigned FromWidth = From->getPrimitiveSizeInBits();
82 unsigned ToWidth = To->getPrimitiveSizeInBits();
83 bool FromLegal = TD->isLegalInteger(FromWidth);
84 bool ToLegal = TD->isLegalInteger(ToWidth);
86 // If this is a legal integer from type, and the result would be an illegal
87 // type, don't do the transformation.
88 if (FromLegal && !ToLegal)
91 // Otherwise, if both are illegal, do not increase the size of the result. We
92 // do allow things like i160 -> i64, but not i64 -> i160.
93 if (!FromLegal && !ToLegal && ToWidth > FromWidth)
100 // SimplifyCommutative - This performs a few simplifications for commutative
103 // 1. Order operands such that they are listed from right (least complex) to
104 // left (most complex). This puts constants before unary operators before
107 // 2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2))
108 // 3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
110 bool InstCombiner::SimplifyCommutative(BinaryOperator &I) {
111 bool Changed = false;
112 if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
113 Changed = !I.swapOperands();
115 if (!I.isAssociative()) return Changed;
117 Instruction::BinaryOps Opcode = I.getOpcode();
118 if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0)))
119 if (Op->getOpcode() == Opcode && isa<Constant>(Op->getOperand(1))) {
120 if (isa<Constant>(I.getOperand(1))) {
121 Constant *Folded = ConstantExpr::get(I.getOpcode(),
122 cast<Constant>(I.getOperand(1)),
123 cast<Constant>(Op->getOperand(1)));
124 I.setOperand(0, Op->getOperand(0));
125 I.setOperand(1, Folded);
129 if (BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1)))
130 if (Op1->getOpcode() == Opcode && isa<Constant>(Op1->getOperand(1)) &&
131 Op->hasOneUse() && Op1->hasOneUse()) {
132 Constant *C1 = cast<Constant>(Op->getOperand(1));
133 Constant *C2 = cast<Constant>(Op1->getOperand(1));
135 // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
136 Constant *Folded = ConstantExpr::get(I.getOpcode(), C1, C2);
137 Instruction *New = BinaryOperator::Create(Opcode, Op->getOperand(0),
141 I.setOperand(0, New);
142 I.setOperand(1, Folded);
149 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
150 // if the LHS is a constant zero (which is the 'negate' form).
152 Value *InstCombiner::dyn_castNegVal(Value *V) const {
153 if (BinaryOperator::isNeg(V))
154 return BinaryOperator::getNegArgument(V);
156 // Constants can be considered to be negated values if they can be folded.
157 if (ConstantInt *C = dyn_cast<ConstantInt>(V))
158 return ConstantExpr::getNeg(C);
160 if (ConstantVector *C = dyn_cast<ConstantVector>(V))
161 if (C->getType()->getElementType()->isIntegerTy())
162 return ConstantExpr::getNeg(C);
167 // dyn_castFNegVal - Given a 'fsub' instruction, return the RHS of the
168 // instruction if the LHS is a constant negative zero (which is the 'negate'
171 Value *InstCombiner::dyn_castFNegVal(Value *V) const {
172 if (BinaryOperator::isFNeg(V))
173 return BinaryOperator::getFNegArgument(V);
175 // Constants can be considered to be negated values if they can be folded.
176 if (ConstantFP *C = dyn_cast<ConstantFP>(V))
177 return ConstantExpr::getFNeg(C);
179 if (ConstantVector *C = dyn_cast<ConstantVector>(V))
180 if (C->getType()->getElementType()->isFloatingPointTy())
181 return ConstantExpr::getFNeg(C);
186 static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO,
188 if (CastInst *CI = dyn_cast<CastInst>(&I))
189 return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType());
191 // Figure out if the constant is the left or the right argument.
192 bool ConstIsRHS = isa<Constant>(I.getOperand(1));
193 Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
195 if (Constant *SOC = dyn_cast<Constant>(SO)) {
197 return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand);
198 return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC);
201 Value *Op0 = SO, *Op1 = ConstOperand;
205 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
206 return IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1,
207 SO->getName()+".op");
208 if (ICmpInst *CI = dyn_cast<ICmpInst>(&I))
209 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
210 SO->getName()+".cmp");
211 if (FCmpInst *CI = dyn_cast<FCmpInst>(&I))
212 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
213 SO->getName()+".cmp");
214 llvm_unreachable("Unknown binary instruction type!");
217 // FoldOpIntoSelect - Given an instruction with a select as one operand and a
218 // constant as the other operand, try to fold the binary operator into the
219 // select arguments. This also works for Cast instructions, which obviously do
220 // not have a second operand.
221 Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
222 // Don't modify shared select instructions
223 if (!SI->hasOneUse()) return 0;
224 Value *TV = SI->getOperand(1);
225 Value *FV = SI->getOperand(2);
227 if (isa<Constant>(TV) || isa<Constant>(FV)) {
228 // Bool selects with constant operands can be folded to logical ops.
229 if (SI->getType()->isIntegerTy(1)) return 0;
231 Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
232 Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
234 return SelectInst::Create(SI->getCondition(), SelectTrueVal,
241 /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
242 /// has a PHI node as operand #0, see if we can fold the instruction into the
243 /// PHI (which is only possible if all operands to the PHI are constants).
245 /// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms
246 /// that would normally be unprofitable because they strongly encourage jump
248 Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
249 bool AllowAggressive) {
250 AllowAggressive = false;
251 PHINode *PN = cast<PHINode>(I.getOperand(0));
252 unsigned NumPHIValues = PN->getNumIncomingValues();
253 if (NumPHIValues == 0 ||
254 // We normally only transform phis with a single use, unless we're trying
255 // hard to make jump threading happen.
256 (!PN->hasOneUse() && !AllowAggressive))
260 // Check to see if all of the operands of the PHI are simple constants
261 // (constantint/constantfp/undef). If there is one non-constant value,
262 // remember the BB it is in. If there is more than one or if *it* is a PHI,
263 // bail out. We don't do arbitrary constant expressions here because moving
264 // their computation can be expensive without a cost model.
265 BasicBlock *NonConstBB = 0;
266 for (unsigned i = 0; i != NumPHIValues; ++i)
267 if (!isa<Constant>(PN->getIncomingValue(i)) ||
268 isa<ConstantExpr>(PN->getIncomingValue(i))) {
269 if (NonConstBB) return 0; // More than one non-const value.
270 if (isa<PHINode>(PN->getIncomingValue(i))) return 0; // Itself a phi.
271 NonConstBB = PN->getIncomingBlock(i);
273 // If the incoming non-constant value is in I's block, we have an infinite
275 if (NonConstBB == I.getParent())
279 // If there is exactly one non-constant value, we can insert a copy of the
280 // operation in that block. However, if this is a critical edge, we would be
281 // inserting the computation one some other paths (e.g. inside a loop). Only
282 // do this if the pred block is unconditionally branching into the phi block.
283 if (NonConstBB != 0 && !AllowAggressive) {
284 BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
285 if (!BI || !BI->isUnconditional()) return 0;
288 // Okay, we can do the transformation: create the new PHI node.
289 PHINode *NewPN = PHINode::Create(I.getType(), "");
290 NewPN->reserveOperandSpace(PN->getNumOperands()/2);
291 InsertNewInstBefore(NewPN, *PN);
294 // Next, add all of the operands to the PHI.
295 if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
296 // We only currently try to fold the condition of a select when it is a phi,
297 // not the true/false values.
298 Value *TrueV = SI->getTrueValue();
299 Value *FalseV = SI->getFalseValue();
300 BasicBlock *PhiTransBB = PN->getParent();
301 for (unsigned i = 0; i != NumPHIValues; ++i) {
302 BasicBlock *ThisBB = PN->getIncomingBlock(i);
303 Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
304 Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
306 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
307 InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
309 assert(PN->getIncomingBlock(i) == NonConstBB);
310 InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred,
312 "phitmp", NonConstBB->getTerminator());
313 Worklist.Add(cast<Instruction>(InV));
315 NewPN->addIncoming(InV, ThisBB);
317 } else if (I.getNumOperands() == 2) {
318 Constant *C = cast<Constant>(I.getOperand(1));
319 for (unsigned i = 0; i != NumPHIValues; ++i) {
321 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
322 if (CmpInst *CI = dyn_cast<CmpInst>(&I))
323 InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
325 InV = ConstantExpr::get(I.getOpcode(), InC, C);
327 assert(PN->getIncomingBlock(i) == NonConstBB);
328 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
329 InV = BinaryOperator::Create(BO->getOpcode(),
330 PN->getIncomingValue(i), C, "phitmp",
331 NonConstBB->getTerminator());
332 else if (CmpInst *CI = dyn_cast<CmpInst>(&I))
333 InV = CmpInst::Create(CI->getOpcode(),
335 PN->getIncomingValue(i), C, "phitmp",
336 NonConstBB->getTerminator());
338 llvm_unreachable("Unknown binop!");
340 Worklist.Add(cast<Instruction>(InV));
342 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
345 CastInst *CI = cast<CastInst>(&I);
346 const Type *RetTy = CI->getType();
347 for (unsigned i = 0; i != NumPHIValues; ++i) {
349 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
350 InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
352 assert(PN->getIncomingBlock(i) == NonConstBB);
353 InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i),
354 I.getType(), "phitmp",
355 NonConstBB->getTerminator());
356 Worklist.Add(cast<Instruction>(InV));
358 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
361 return ReplaceInstUsesWith(I, NewPN);
364 /// FindElementAtOffset - Given a type and a constant offset, determine whether
365 /// or not there is a sequence of GEP indices into the type that will land us at
366 /// the specified offset. If so, fill them into NewIndices and return the
367 /// resultant element type, otherwise return null.
368 const Type *InstCombiner::FindElementAtOffset(const Type *Ty, int64_t Offset,
369 SmallVectorImpl<Value*> &NewIndices) {
371 if (!Ty->isSized()) return 0;
373 // Start with the index over the outer type. Note that the type size
374 // might be zero (even if the offset isn't zero) if the indexed type
375 // is something like [0 x {int, int}]
376 const Type *IntPtrTy = TD->getIntPtrType(Ty->getContext());
377 int64_t FirstIdx = 0;
378 if (int64_t TySize = TD->getTypeAllocSize(Ty)) {
379 FirstIdx = Offset/TySize;
380 Offset -= FirstIdx*TySize;
382 // Handle hosts where % returns negative instead of values [0..TySize).
388 assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
391 NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
393 // Index into the types. If we fail, set OrigBase to null.
395 // Indexing into tail padding between struct/array elements.
396 if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty))
399 if (const StructType *STy = dyn_cast<StructType>(Ty)) {
400 const StructLayout *SL = TD->getStructLayout(STy);
401 assert(Offset < (int64_t)SL->getSizeInBytes() &&
402 "Offset must stay within the indexed type");
404 unsigned Elt = SL->getElementContainingOffset(Offset);
405 NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
408 Offset -= SL->getElementOffset(Elt);
409 Ty = STy->getElementType(Elt);
410 } else if (const ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
411 uint64_t EltSize = TD->getTypeAllocSize(AT->getElementType());
412 assert(EltSize && "Cannot index into a zero-sized array");
413 NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
415 Ty = AT->getElementType();
417 // Otherwise, we can't index into the middle of this atomic type, bail.
427 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
428 SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
430 if (Value *V = SimplifyGEPInst(&Ops[0], Ops.size(), TD))
431 return ReplaceInstUsesWith(GEP, V);
433 Value *PtrOp = GEP.getOperand(0);
435 if (isa<UndefValue>(GEP.getOperand(0)))
436 return ReplaceInstUsesWith(GEP, UndefValue::get(GEP.getType()));
438 // Eliminate unneeded casts for indices.
440 bool MadeChange = false;
441 unsigned PtrSize = TD->getPointerSizeInBits();
443 gep_type_iterator GTI = gep_type_begin(GEP);
444 for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end();
445 I != E; ++I, ++GTI) {
446 if (!isa<SequentialType>(*GTI)) continue;
448 // If we are using a wider index than needed for this platform, shrink it
449 // to what we need. If narrower, sign-extend it to what we need. This
450 // explicit cast can make subsequent optimizations more obvious.
451 unsigned OpBits = cast<IntegerType>((*I)->getType())->getBitWidth();
452 if (OpBits == PtrSize)
455 *I = Builder->CreateIntCast(*I, TD->getIntPtrType(GEP.getContext()),true);
458 if (MadeChange) return &GEP;
461 // Combine Indices - If the source pointer to this getelementptr instruction
462 // is a getelementptr instruction, combine the indices of the two
463 // getelementptr instructions into a single instruction.
465 if (GEPOperator *Src = dyn_cast<GEPOperator>(PtrOp)) {
466 // Note that if our source is a gep chain itself that we wait for that
467 // chain to be resolved before we perform this transformation. This
468 // avoids us creating a TON of code in some cases.
470 if (GetElementPtrInst *SrcGEP =
471 dyn_cast<GetElementPtrInst>(Src->getOperand(0)))
472 if (SrcGEP->getNumOperands() == 2)
473 return 0; // Wait until our source is folded to completion.
475 SmallVector<Value*, 8> Indices;
477 // Find out whether the last index in the source GEP is a sequential idx.
478 bool EndsWithSequential = false;
479 for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
481 EndsWithSequential = !(*I)->isStructTy();
483 // Can we combine the two pointer arithmetics offsets?
484 if (EndsWithSequential) {
485 // Replace: gep (gep %P, long B), long A, ...
486 // With: T = long A+B; gep %P, T, ...
489 Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
490 Value *GO1 = GEP.getOperand(1);
491 if (SO1 == Constant::getNullValue(SO1->getType())) {
493 } else if (GO1 == Constant::getNullValue(GO1->getType())) {
496 // If they aren't the same type, then the input hasn't been processed
497 // by the loop above yet (which canonicalizes sequential index types to
498 // intptr_t). Just avoid transforming this until the input has been
500 if (SO1->getType() != GO1->getType())
502 Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
505 // Update the GEP in place if possible.
506 if (Src->getNumOperands() == 2) {
507 GEP.setOperand(0, Src->getOperand(0));
508 GEP.setOperand(1, Sum);
511 Indices.append(Src->op_begin()+1, Src->op_end()-1);
512 Indices.push_back(Sum);
513 Indices.append(GEP.op_begin()+2, GEP.op_end());
514 } else if (isa<Constant>(*GEP.idx_begin()) &&
515 cast<Constant>(*GEP.idx_begin())->isNullValue() &&
516 Src->getNumOperands() != 1) {
517 // Otherwise we can do the fold if the first index of the GEP is a zero
518 Indices.append(Src->op_begin()+1, Src->op_end());
519 Indices.append(GEP.idx_begin()+1, GEP.idx_end());
522 if (!Indices.empty())
523 return (GEP.isInBounds() && Src->isInBounds()) ?
524 GetElementPtrInst::CreateInBounds(Src->getOperand(0), Indices.begin(),
525 Indices.end(), GEP.getName()) :
526 GetElementPtrInst::Create(Src->getOperand(0), Indices.begin(),
527 Indices.end(), GEP.getName());
530 // Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
531 Value *StrippedPtr = PtrOp->stripPointerCasts();
532 if (StrippedPtr != PtrOp) {
533 const PointerType *StrippedPtrTy =cast<PointerType>(StrippedPtr->getType());
535 bool HasZeroPointerIndex = false;
536 if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
537 HasZeroPointerIndex = C->isZero();
539 // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
540 // into : GEP [10 x i8]* X, i32 0, ...
542 // Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
543 // into : GEP i8* X, ...
545 // This occurs when the program declares an array extern like "int X[];"
546 if (HasZeroPointerIndex) {
547 const PointerType *CPTy = cast<PointerType>(PtrOp->getType());
548 if (const ArrayType *CATy =
549 dyn_cast<ArrayType>(CPTy->getElementType())) {
550 // GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
551 if (CATy->getElementType() == StrippedPtrTy->getElementType()) {
553 SmallVector<Value*, 8> Idx(GEP.idx_begin()+1, GEP.idx_end());
554 GetElementPtrInst *Res =
555 GetElementPtrInst::Create(StrippedPtr, Idx.begin(),
556 Idx.end(), GEP.getName());
557 Res->setIsInBounds(GEP.isInBounds());
561 if (const ArrayType *XATy =
562 dyn_cast<ArrayType>(StrippedPtrTy->getElementType())){
563 // GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
564 if (CATy->getElementType() == XATy->getElementType()) {
565 // -> GEP [10 x i8]* X, i32 0, ...
566 // At this point, we know that the cast source type is a pointer
567 // to an array of the same type as the destination pointer
568 // array. Because the array type is never stepped over (there
569 // is a leading zero) we can fold the cast into this GEP.
570 GEP.setOperand(0, StrippedPtr);
575 } else if (GEP.getNumOperands() == 2) {
576 // Transform things like:
577 // %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
578 // into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
579 const Type *SrcElTy = StrippedPtrTy->getElementType();
580 const Type *ResElTy=cast<PointerType>(PtrOp->getType())->getElementType();
581 if (TD && SrcElTy->isArrayTy() &&
582 TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType()) ==
583 TD->getTypeAllocSize(ResElTy)) {
585 Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
586 Idx[1] = GEP.getOperand(1);
587 Value *NewGEP = GEP.isInBounds() ?
588 Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()) :
589 Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
590 // V and GEP are both pointer types --> BitCast
591 return new BitCastInst(NewGEP, GEP.getType());
594 // Transform things like:
595 // getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
596 // (where tmp = 8*tmp2) into:
597 // getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
599 if (TD && SrcElTy->isArrayTy() && ResElTy->isIntegerTy(8)) {
600 uint64_t ArrayEltSize =
601 TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType());
603 // Check to see if "tmp" is a scale by a multiple of ArrayEltSize. We
604 // allow either a mul, shift, or constant here.
606 ConstantInt *Scale = 0;
607 if (ArrayEltSize == 1) {
608 NewIdx = GEP.getOperand(1);
609 Scale = ConstantInt::get(cast<IntegerType>(NewIdx->getType()), 1);
610 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP.getOperand(1))) {
611 NewIdx = ConstantInt::get(CI->getType(), 1);
613 } else if (Instruction *Inst =dyn_cast<Instruction>(GEP.getOperand(1))){
614 if (Inst->getOpcode() == Instruction::Shl &&
615 isa<ConstantInt>(Inst->getOperand(1))) {
616 ConstantInt *ShAmt = cast<ConstantInt>(Inst->getOperand(1));
617 uint32_t ShAmtVal = ShAmt->getLimitedValue(64);
618 Scale = ConstantInt::get(cast<IntegerType>(Inst->getType()),
620 NewIdx = Inst->getOperand(0);
621 } else if (Inst->getOpcode() == Instruction::Mul &&
622 isa<ConstantInt>(Inst->getOperand(1))) {
623 Scale = cast<ConstantInt>(Inst->getOperand(1));
624 NewIdx = Inst->getOperand(0);
628 // If the index will be to exactly the right offset with the scale taken
629 // out, perform the transformation. Note, we don't know whether Scale is
630 // signed or not. We'll use unsigned version of division/modulo
631 // operation after making sure Scale doesn't have the sign bit set.
632 if (ArrayEltSize && Scale && Scale->getSExtValue() >= 0LL &&
633 Scale->getZExtValue() % ArrayEltSize == 0) {
634 Scale = ConstantInt::get(Scale->getType(),
635 Scale->getZExtValue() / ArrayEltSize);
636 if (Scale->getZExtValue() != 1) {
637 Constant *C = ConstantExpr::getIntegerCast(Scale, NewIdx->getType(),
639 NewIdx = Builder->CreateMul(NewIdx, C, "idxscale");
642 // Insert the new GEP instruction.
644 Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
646 Value *NewGEP = GEP.isInBounds() ?
647 Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2,GEP.getName()):
648 Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
649 // The NewGEP must be pointer typed, so must the old one -> BitCast
650 return new BitCastInst(NewGEP, GEP.getType());
656 /// See if we can simplify:
657 /// X = bitcast A* to B*
658 /// Y = gep X, <...constant indices...>
659 /// into a gep of the original struct. This is important for SROA and alias
660 /// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
661 if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
663 !isa<BitCastInst>(BCI->getOperand(0)) && GEP.hasAllConstantIndices()) {
664 // Determine how much the GEP moves the pointer. We are guaranteed to get
665 // a constant back from EmitGEPOffset.
666 ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(&GEP));
667 int64_t Offset = OffsetV->getSExtValue();
669 // If this GEP instruction doesn't move the pointer, just replace the GEP
670 // with a bitcast of the real input to the dest type.
672 // If the bitcast is of an allocation, and the allocation will be
673 // converted to match the type of the cast, don't touch this.
674 if (isa<AllocaInst>(BCI->getOperand(0)) ||
675 isMalloc(BCI->getOperand(0))) {
676 // See if the bitcast simplifies, if so, don't nuke this GEP yet.
677 if (Instruction *I = visitBitCast(*BCI)) {
680 BCI->getParent()->getInstList().insert(BCI, I);
681 ReplaceInstUsesWith(*BCI, I);
686 return new BitCastInst(BCI->getOperand(0), GEP.getType());
689 // Otherwise, if the offset is non-zero, we need to find out if there is a
690 // field at Offset in 'A's type. If so, we can pull the cast through the
692 SmallVector<Value*, 8> NewIndices;
694 cast<PointerType>(BCI->getOperand(0)->getType())->getElementType();
695 if (FindElementAtOffset(InTy, Offset, NewIndices)) {
696 Value *NGEP = GEP.isInBounds() ?
697 Builder->CreateInBoundsGEP(BCI->getOperand(0), NewIndices.begin(),
699 Builder->CreateGEP(BCI->getOperand(0), NewIndices.begin(),
702 if (NGEP->getType() == GEP.getType())
703 return ReplaceInstUsesWith(GEP, NGEP);
704 NGEP->takeName(&GEP);
705 return new BitCastInst(NGEP, GEP.getType());
715 static bool IsOnlyNullComparedAndFreed(const Value &V) {
716 for (Value::const_use_iterator UI = V.use_begin(), UE = V.use_end();
720 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(*UI))
721 if (ICI->isEquality() && isa<ConstantPointerNull>(ICI->getOperand(1)))
728 Instruction *InstCombiner::visitMalloc(Instruction &MI) {
729 // If we have a malloc call which is only used in any amount of comparisons
730 // to null and free calls, delete the calls and replace the comparisons with
731 // true or false as appropriate.
732 if (IsOnlyNullComparedAndFreed(MI)) {
733 for (Value::use_iterator UI = MI.use_begin(), UE = MI.use_end();
735 // We can assume that every remaining use is a free call or an icmp eq/ne
736 // to null, so the cast is safe.
737 Instruction *I = cast<Instruction>(*UI);
739 // Early increment here, as we're about to get rid of the user.
743 EraseInstFromFunction(*cast<CallInst>(I));
746 // Again, the cast is safe.
747 ICmpInst *C = cast<ICmpInst>(I);
748 ReplaceInstUsesWith(*C, ConstantInt::get(Type::getInt1Ty(C->getContext()),
749 C->isFalseWhenEqual()));
750 EraseInstFromFunction(*C);
752 return EraseInstFromFunction(MI);
759 Instruction *InstCombiner::visitFree(CallInst &FI) {
760 Value *Op = FI.getArgOperand(0);
762 // free undef -> unreachable.
763 if (isa<UndefValue>(Op)) {
764 // Insert a new store to null because we cannot modify the CFG here.
765 new StoreInst(ConstantInt::getTrue(FI.getContext()),
766 UndefValue::get(Type::getInt1PtrTy(FI.getContext())), &FI);
767 return EraseInstFromFunction(FI);
770 // If we have 'free null' delete the instruction. This can happen in stl code
771 // when lots of inlining happens.
772 if (isa<ConstantPointerNull>(Op))
773 return EraseInstFromFunction(FI);
780 Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
781 // Change br (not X), label True, label False to: br X, label False, True
783 BasicBlock *TrueDest;
784 BasicBlock *FalseDest;
785 if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) &&
787 // Swap Destinations and condition...
789 BI.setSuccessor(0, FalseDest);
790 BI.setSuccessor(1, TrueDest);
794 // Cannonicalize fcmp_one -> fcmp_oeq
795 FCmpInst::Predicate FPred; Value *Y;
796 if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)),
797 TrueDest, FalseDest)) &&
798 BI.getCondition()->hasOneUse())
799 if (FPred == FCmpInst::FCMP_ONE || FPred == FCmpInst::FCMP_OLE ||
800 FPred == FCmpInst::FCMP_OGE) {
801 FCmpInst *Cond = cast<FCmpInst>(BI.getCondition());
802 Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
804 // Swap Destinations and condition.
805 BI.setSuccessor(0, FalseDest);
806 BI.setSuccessor(1, TrueDest);
811 // Cannonicalize icmp_ne -> icmp_eq
812 ICmpInst::Predicate IPred;
813 if (match(&BI, m_Br(m_ICmp(IPred, m_Value(X), m_Value(Y)),
814 TrueDest, FalseDest)) &&
815 BI.getCondition()->hasOneUse())
816 if (IPred == ICmpInst::ICMP_NE || IPred == ICmpInst::ICMP_ULE ||
817 IPred == ICmpInst::ICMP_SLE || IPred == ICmpInst::ICMP_UGE ||
818 IPred == ICmpInst::ICMP_SGE) {
819 ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
820 Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
821 // Swap Destinations and condition.
822 BI.setSuccessor(0, FalseDest);
823 BI.setSuccessor(1, TrueDest);
831 Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
832 Value *Cond = SI.getCondition();
833 if (Instruction *I = dyn_cast<Instruction>(Cond)) {
834 if (I->getOpcode() == Instruction::Add)
835 if (ConstantInt *AddRHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
836 // change 'switch (X+4) case 1:' into 'switch (X) case -3'
837 for (unsigned i = 2, e = SI.getNumOperands(); i != e; i += 2)
839 ConstantExpr::getSub(cast<Constant>(SI.getOperand(i)),
841 SI.setOperand(0, I->getOperand(0));
849 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
850 Value *Agg = EV.getAggregateOperand();
852 if (!EV.hasIndices())
853 return ReplaceInstUsesWith(EV, Agg);
855 if (Constant *C = dyn_cast<Constant>(Agg)) {
856 if (isa<UndefValue>(C))
857 return ReplaceInstUsesWith(EV, UndefValue::get(EV.getType()));
859 if (isa<ConstantAggregateZero>(C))
860 return ReplaceInstUsesWith(EV, Constant::getNullValue(EV.getType()));
862 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
863 // Extract the element indexed by the first index out of the constant
864 Value *V = C->getOperand(*EV.idx_begin());
865 if (EV.getNumIndices() > 1)
866 // Extract the remaining indices out of the constant indexed by the
868 return ExtractValueInst::Create(V, EV.idx_begin() + 1, EV.idx_end());
870 return ReplaceInstUsesWith(EV, V);
872 return 0; // Can't handle other constants
874 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
875 // We're extracting from an insertvalue instruction, compare the indices
876 const unsigned *exti, *exte, *insi, *inse;
877 for (exti = EV.idx_begin(), insi = IV->idx_begin(),
878 exte = EV.idx_end(), inse = IV->idx_end();
879 exti != exte && insi != inse;
882 // The insert and extract both reference distinctly different elements.
883 // This means the extract is not influenced by the insert, and we can
884 // replace the aggregate operand of the extract with the aggregate
885 // operand of the insert. i.e., replace
886 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
887 // %E = extractvalue { i32, { i32 } } %I, 0
889 // %E = extractvalue { i32, { i32 } } %A, 0
890 return ExtractValueInst::Create(IV->getAggregateOperand(),
891 EV.idx_begin(), EV.idx_end());
893 if (exti == exte && insi == inse)
894 // Both iterators are at the end: Index lists are identical. Replace
895 // %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
896 // %C = extractvalue { i32, { i32 } } %B, 1, 0
898 return ReplaceInstUsesWith(EV, IV->getInsertedValueOperand());
900 // The extract list is a prefix of the insert list. i.e. replace
901 // %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
902 // %E = extractvalue { i32, { i32 } } %I, 1
904 // %X = extractvalue { i32, { i32 } } %A, 1
905 // %E = insertvalue { i32 } %X, i32 42, 0
906 // by switching the order of the insert and extract (though the
907 // insertvalue should be left in, since it may have other uses).
908 Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(),
909 EV.idx_begin(), EV.idx_end());
910 return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
914 // The insert list is a prefix of the extract list
915 // We can simply remove the common indices from the extract and make it
916 // operate on the inserted value instead of the insertvalue result.
918 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
919 // %E = extractvalue { i32, { i32 } } %I, 1, 0
921 // %E extractvalue { i32 } { i32 42 }, 0
922 return ExtractValueInst::Create(IV->getInsertedValueOperand(),
925 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
926 // We're extracting from an intrinsic, see if we're the only user, which
927 // allows us to simplify multiple result intrinsics to simpler things that
928 // just get one value.
929 if (II->hasOneUse()) {
930 // Check if we're grabbing the overflow bit or the result of a 'with
931 // overflow' intrinsic. If it's the latter we can remove the intrinsic
932 // and replace it with a traditional binary instruction.
933 switch (II->getIntrinsicID()) {
934 case Intrinsic::uadd_with_overflow:
935 case Intrinsic::sadd_with_overflow:
936 if (*EV.idx_begin() == 0) { // Normal result.
937 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
938 II->replaceAllUsesWith(UndefValue::get(II->getType()));
939 EraseInstFromFunction(*II);
940 return BinaryOperator::CreateAdd(LHS, RHS);
943 case Intrinsic::usub_with_overflow:
944 case Intrinsic::ssub_with_overflow:
945 if (*EV.idx_begin() == 0) { // Normal result.
946 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
947 II->replaceAllUsesWith(UndefValue::get(II->getType()));
948 EraseInstFromFunction(*II);
949 return BinaryOperator::CreateSub(LHS, RHS);
952 case Intrinsic::umul_with_overflow:
953 case Intrinsic::smul_with_overflow:
954 if (*EV.idx_begin() == 0) { // Normal result.
955 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
956 II->replaceAllUsesWith(UndefValue::get(II->getType()));
957 EraseInstFromFunction(*II);
958 return BinaryOperator::CreateMul(LHS, RHS);
966 // Can't simplify extracts from other values. Note that nested extracts are
967 // already simplified implicitely by the above (extract ( extract (insert) )
968 // will be translated into extract ( insert ( extract ) ) first and then just
969 // the value inserted, if appropriate).
976 /// TryToSinkInstruction - Try to move the specified instruction from its
977 /// current block into the beginning of DestBlock, which can only happen if it's
978 /// safe to move the instruction past all of the instructions between it and the
979 /// end of its block.
980 static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
981 assert(I->hasOneUse() && "Invariants didn't hold!");
983 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
984 if (isa<PHINode>(I) || I->mayHaveSideEffects() || isa<TerminatorInst>(I))
987 // Do not sink alloca instructions out of the entry block.
988 if (isa<AllocaInst>(I) && I->getParent() ==
989 &DestBlock->getParent()->getEntryBlock())
992 // We can only sink load instructions if there is nothing between the load and
993 // the end of block that could change the value.
994 if (I->mayReadFromMemory()) {
995 for (BasicBlock::iterator Scan = I, E = I->getParent()->end();
997 if (Scan->mayWriteToMemory())
1001 BasicBlock::iterator InsertPos = DestBlock->getFirstNonPHI();
1003 I->moveBefore(InsertPos);
1009 /// AddReachableCodeToWorklist - Walk the function in depth-first order, adding
1010 /// all reachable code to the worklist.
1012 /// This has a couple of tricks to make the code faster and more powerful. In
1013 /// particular, we constant fold and DCE instructions as we go, to avoid adding
1014 /// them to the worklist (this significantly speeds up instcombine on code where
1015 /// many instructions are dead or constant). Additionally, if we find a branch
1016 /// whose condition is a known constant, we only visit the reachable successors.
1018 static bool AddReachableCodeToWorklist(BasicBlock *BB,
1019 SmallPtrSet<BasicBlock*, 64> &Visited,
1021 const TargetData *TD) {
1022 bool MadeIRChange = false;
1023 SmallVector<BasicBlock*, 256> Worklist;
1024 Worklist.push_back(BB);
1026 std::vector<Instruction*> InstrsForInstCombineWorklist;
1027 InstrsForInstCombineWorklist.reserve(128);
1029 SmallPtrSet<ConstantExpr*, 64> FoldedConstants;
1032 BB = Worklist.pop_back_val();
1034 // We have now visited this block! If we've already been here, ignore it.
1035 if (!Visited.insert(BB)) continue;
1037 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) {
1038 Instruction *Inst = BBI++;
1040 // DCE instruction if trivially dead.
1041 if (isInstructionTriviallyDead(Inst)) {
1043 DEBUG(errs() << "IC: DCE: " << *Inst << '\n');
1044 Inst->eraseFromParent();
1048 // ConstantProp instruction if trivially constant.
1049 if (!Inst->use_empty() && isa<Constant>(Inst->getOperand(0)))
1050 if (Constant *C = ConstantFoldInstruction(Inst, TD)) {
1051 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: "
1053 Inst->replaceAllUsesWith(C);
1055 Inst->eraseFromParent();
1060 // See if we can constant fold its operands.
1061 for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end();
1063 ConstantExpr *CE = dyn_cast<ConstantExpr>(i);
1064 if (CE == 0) continue;
1066 // If we already folded this constant, don't try again.
1067 if (!FoldedConstants.insert(CE))
1070 Constant *NewC = ConstantFoldConstantExpression(CE, TD);
1071 if (NewC && NewC != CE) {
1073 MadeIRChange = true;
1078 InstrsForInstCombineWorklist.push_back(Inst);
1081 // Recursively visit successors. If this is a branch or switch on a
1082 // constant, only visit the reachable successor.
1083 TerminatorInst *TI = BB->getTerminator();
1084 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1085 if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
1086 bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
1087 BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
1088 Worklist.push_back(ReachableBB);
1091 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1092 if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
1093 // See if this is an explicit destination.
1094 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
1095 if (SI->getCaseValue(i) == Cond) {
1096 BasicBlock *ReachableBB = SI->getSuccessor(i);
1097 Worklist.push_back(ReachableBB);
1101 // Otherwise it is the default destination.
1102 Worklist.push_back(SI->getSuccessor(0));
1107 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
1108 Worklist.push_back(TI->getSuccessor(i));
1109 } while (!Worklist.empty());
1111 // Once we've found all of the instructions to add to instcombine's worklist,
1112 // add them in reverse order. This way instcombine will visit from the top
1113 // of the function down. This jives well with the way that it adds all uses
1114 // of instructions to the worklist after doing a transformation, thus avoiding
1115 // some N^2 behavior in pathological cases.
1116 IC.Worklist.AddInitialGroup(&InstrsForInstCombineWorklist[0],
1117 InstrsForInstCombineWorklist.size());
1119 return MadeIRChange;
1122 bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {
1123 MadeIRChange = false;
1125 DEBUG(errs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on "
1126 << F.getNameStr() << "\n");
1129 // Do a depth-first traversal of the function, populate the worklist with
1130 // the reachable instructions. Ignore blocks that are not reachable. Keep
1131 // track of which blocks we visit.
1132 SmallPtrSet<BasicBlock*, 64> Visited;
1133 MadeIRChange |= AddReachableCodeToWorklist(F.begin(), Visited, *this, TD);
1135 // Do a quick scan over the function. If we find any blocks that are
1136 // unreachable, remove any instructions inside of them. This prevents
1137 // the instcombine code from having to deal with some bad special cases.
1138 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1139 if (!Visited.count(BB)) {
1140 Instruction *Term = BB->getTerminator();
1141 while (Term != BB->begin()) { // Remove instrs bottom-up
1142 BasicBlock::iterator I = Term; --I;
1144 DEBUG(errs() << "IC: DCE: " << *I << '\n');
1145 // A debug intrinsic shouldn't force another iteration if we weren't
1146 // going to do one without it.
1147 if (!isa<DbgInfoIntrinsic>(I)) {
1149 MadeIRChange = true;
1152 // If I is not void type then replaceAllUsesWith undef.
1153 // This allows ValueHandlers and custom metadata to adjust itself.
1154 if (!I->getType()->isVoidTy())
1155 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1156 I->eraseFromParent();
1161 while (!Worklist.isEmpty()) {
1162 Instruction *I = Worklist.RemoveOne();
1163 if (I == 0) continue; // skip null values.
1165 // Check to see if we can DCE the instruction.
1166 if (isInstructionTriviallyDead(I)) {
1167 DEBUG(errs() << "IC: DCE: " << *I << '\n');
1168 EraseInstFromFunction(*I);
1170 MadeIRChange = true;
1174 // Instruction isn't dead, see if we can constant propagate it.
1175 if (!I->use_empty() && isa<Constant>(I->getOperand(0)))
1176 if (Constant *C = ConstantFoldInstruction(I, TD)) {
1177 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *I << '\n');
1179 // Add operands to the worklist.
1180 ReplaceInstUsesWith(*I, C);
1182 EraseInstFromFunction(*I);
1183 MadeIRChange = true;
1187 // See if we can trivially sink this instruction to a successor basic block.
1188 if (I->hasOneUse()) {
1189 BasicBlock *BB = I->getParent();
1190 Instruction *UserInst = cast<Instruction>(I->use_back());
1191 BasicBlock *UserParent;
1193 // Get the block the use occurs in.
1194 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
1195 UserParent = PN->getIncomingBlock(I->use_begin().getUse());
1197 UserParent = UserInst->getParent();
1199 if (UserParent != BB) {
1200 bool UserIsSuccessor = false;
1201 // See if the user is one of our successors.
1202 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1203 if (*SI == UserParent) {
1204 UserIsSuccessor = true;
1208 // If the user is one of our immediate successors, and if that successor
1209 // only has us as a predecessors (we'd have to split the critical edge
1210 // otherwise), we can keep going.
1211 if (UserIsSuccessor && UserParent->getSinglePredecessor())
1212 // Okay, the CFG is simple enough, try to sink this instruction.
1213 MadeIRChange |= TryToSinkInstruction(I, UserParent);
1217 // Now that we have an instruction, try combining it to simplify it.
1218 Builder->SetInsertPoint(I->getParent(), I);
1223 DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
1224 DEBUG(errs() << "IC: Visiting: " << OrigI << '\n');
1226 if (Instruction *Result = visit(*I)) {
1228 // Should we replace the old instruction with a new one?
1230 DEBUG(errs() << "IC: Old = " << *I << '\n'
1231 << " New = " << *Result << '\n');
1233 // Everything uses the new instruction now.
1234 I->replaceAllUsesWith(Result);
1236 // Push the new instruction and any users onto the worklist.
1237 Worklist.Add(Result);
1238 Worklist.AddUsersToWorkList(*Result);
1240 // Move the name to the new instruction first.
1241 Result->takeName(I);
1243 // Insert the new instruction into the basic block...
1244 BasicBlock *InstParent = I->getParent();
1245 BasicBlock::iterator InsertPos = I;
1247 if (!isa<PHINode>(Result)) // If combining a PHI, don't insert
1248 while (isa<PHINode>(InsertPos)) // middle of a block of PHIs.
1251 InstParent->getInstList().insert(InsertPos, Result);
1253 EraseInstFromFunction(*I);
1256 DEBUG(errs() << "IC: Mod = " << OrigI << '\n'
1257 << " New = " << *I << '\n');
1260 // If the instruction was modified, it's possible that it is now dead.
1261 // if so, remove it.
1262 if (isInstructionTriviallyDead(I)) {
1263 EraseInstFromFunction(*I);
1266 Worklist.AddUsersToWorkList(*I);
1269 MadeIRChange = true;
1274 return MadeIRChange;
1278 bool InstCombiner::runOnFunction(Function &F) {
1279 MustPreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
1280 TD = getAnalysisIfAvailable<TargetData>();
1283 /// Builder - This is an IRBuilder that automatically inserts new
1284 /// instructions into the worklist when they are created.
1285 IRBuilder<true, TargetFolder, InstCombineIRInserter>
1286 TheBuilder(F.getContext(), TargetFolder(TD),
1287 InstCombineIRInserter(Worklist));
1288 Builder = &TheBuilder;
1290 bool EverMadeChange = false;
1292 // Iterate while there is work to do.
1293 unsigned Iteration = 0;
1294 while (DoOneIteration(F, Iteration++))
1295 EverMadeChange = true;
1298 return EverMadeChange;
1301 FunctionPass *llvm::createInstructionCombiningPass() {
1302 return new InstCombiner();