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"
51 #include "llvm-c/Initialization.h"
55 using namespace llvm::PatternMatch;
57 STATISTIC(NumCombined , "Number of insts combined");
58 STATISTIC(NumConstProp, "Number of constant folds");
59 STATISTIC(NumDeadInst , "Number of dead inst eliminated");
60 STATISTIC(NumSunkInst , "Number of instructions sunk");
62 // Initialization Routines
63 void llvm::initializeInstCombine(PassRegistry &Registry) {
64 initializeInstCombinerPass(Registry);
67 void LLVMInitializeInstCombine(LLVMPassRegistryRef R) {
68 initializeInstCombine(*unwrap(R));
71 char InstCombiner::ID = 0;
72 INITIALIZE_PASS(InstCombiner, "instcombine",
73 "Combine redundant instructions", false, false)
75 void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
76 AU.addPreservedID(LCSSAID);
81 /// ShouldChangeType - Return true if it is desirable to convert a computation
82 /// from 'From' to 'To'. We don't want to convert from a legal to an illegal
83 /// type for example, or from a smaller to a larger illegal type.
84 bool InstCombiner::ShouldChangeType(const Type *From, const Type *To) const {
85 assert(From->isIntegerTy() && To->isIntegerTy());
87 // If we don't have TD, we don't know if the source/dest are legal.
88 if (!TD) return false;
90 unsigned FromWidth = From->getPrimitiveSizeInBits();
91 unsigned ToWidth = To->getPrimitiveSizeInBits();
92 bool FromLegal = TD->isLegalInteger(FromWidth);
93 bool ToLegal = TD->isLegalInteger(ToWidth);
95 // If this is a legal integer from type, and the result would be an illegal
96 // type, don't do the transformation.
97 if (FromLegal && !ToLegal)
100 // Otherwise, if both are illegal, do not increase the size of the result. We
101 // do allow things like i160 -> i64, but not i64 -> i160.
102 if (!FromLegal && !ToLegal && ToWidth > FromWidth)
109 /// SimplifyAssociativeOrCommutative - This performs a few simplifications for
110 /// operators which are associative or commutative:
112 // Commutative operators:
114 // 1. Order operands such that they are listed from right (least complex) to
115 // left (most complex). This puts constants before unary operators before
118 // Associative operators:
120 // 2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
121 // 3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
123 // Associative and commutative operators:
125 // 4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
126 // 5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
127 // 6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
128 // if C1 and C2 are constants.
130 bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
131 Instruction::BinaryOps Opcode = I.getOpcode();
132 bool Changed = false;
135 // Order operands such that they are listed from right (least complex) to
136 // left (most complex). This puts constants before unary operators before
138 if (I.isCommutative() && getComplexity(I.getOperand(0)) <
139 getComplexity(I.getOperand(1)))
140 Changed = !I.swapOperands();
142 BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
143 BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
145 if (I.isAssociative()) {
146 // Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
147 if (Op0 && Op0->getOpcode() == Opcode) {
148 Value *A = Op0->getOperand(0);
149 Value *B = Op0->getOperand(1);
150 Value *C = I.getOperand(1);
152 // Does "B op C" simplify?
153 if (Value *V = SimplifyBinOp(Opcode, B, C, TD)) {
154 // It simplifies to V. Form "A op V".
162 // Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
163 if (Op1 && Op1->getOpcode() == Opcode) {
164 Value *A = I.getOperand(0);
165 Value *B = Op1->getOperand(0);
166 Value *C = Op1->getOperand(1);
168 // Does "A op B" simplify?
169 if (Value *V = SimplifyBinOp(Opcode, A, B, TD)) {
170 // It simplifies to V. Form "V op C".
179 if (I.isAssociative() && I.isCommutative()) {
180 // Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
181 if (Op0 && Op0->getOpcode() == Opcode) {
182 Value *A = Op0->getOperand(0);
183 Value *B = Op0->getOperand(1);
184 Value *C = I.getOperand(1);
186 // Does "C op A" simplify?
187 if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
188 // It simplifies to V. Form "V op B".
196 // Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
197 if (Op1 && Op1->getOpcode() == Opcode) {
198 Value *A = I.getOperand(0);
199 Value *B = Op1->getOperand(0);
200 Value *C = Op1->getOperand(1);
202 // Does "C op A" simplify?
203 if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
204 // It simplifies to V. Form "B op V".
212 // Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
213 // if C1 and C2 are constants.
215 Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
216 isa<Constant>(Op0->getOperand(1)) &&
217 isa<Constant>(Op1->getOperand(1)) &&
218 Op0->hasOneUse() && Op1->hasOneUse()) {
219 Value *A = Op0->getOperand(0);
220 Constant *C1 = cast<Constant>(Op0->getOperand(1));
221 Value *B = Op1->getOperand(0);
222 Constant *C2 = cast<Constant>(Op1->getOperand(1));
224 Constant *Folded = ConstantExpr::get(Opcode, C1, C2);
225 Instruction *New = BinaryOperator::Create(Opcode, A, B, Op1->getName(),
228 I.setOperand(0, New);
229 I.setOperand(1, Folded);
235 // No further simplifications.
240 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
241 // if the LHS is a constant zero (which is the 'negate' form).
243 Value *InstCombiner::dyn_castNegVal(Value *V) const {
244 if (BinaryOperator::isNeg(V))
245 return BinaryOperator::getNegArgument(V);
247 // Constants can be considered to be negated values if they can be folded.
248 if (ConstantInt *C = dyn_cast<ConstantInt>(V))
249 return ConstantExpr::getNeg(C);
251 if (ConstantVector *C = dyn_cast<ConstantVector>(V))
252 if (C->getType()->getElementType()->isIntegerTy())
253 return ConstantExpr::getNeg(C);
258 // dyn_castFNegVal - Given a 'fsub' instruction, return the RHS of the
259 // instruction if the LHS is a constant negative zero (which is the 'negate'
262 Value *InstCombiner::dyn_castFNegVal(Value *V) const {
263 if (BinaryOperator::isFNeg(V))
264 return BinaryOperator::getFNegArgument(V);
266 // Constants can be considered to be negated values if they can be folded.
267 if (ConstantFP *C = dyn_cast<ConstantFP>(V))
268 return ConstantExpr::getFNeg(C);
270 if (ConstantVector *C = dyn_cast<ConstantVector>(V))
271 if (C->getType()->getElementType()->isFloatingPointTy())
272 return ConstantExpr::getFNeg(C);
277 static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO,
279 if (CastInst *CI = dyn_cast<CastInst>(&I))
280 return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType());
282 // Figure out if the constant is the left or the right argument.
283 bool ConstIsRHS = isa<Constant>(I.getOperand(1));
284 Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
286 if (Constant *SOC = dyn_cast<Constant>(SO)) {
288 return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand);
289 return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC);
292 Value *Op0 = SO, *Op1 = ConstOperand;
296 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
297 return IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1,
298 SO->getName()+".op");
299 if (ICmpInst *CI = dyn_cast<ICmpInst>(&I))
300 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
301 SO->getName()+".cmp");
302 if (FCmpInst *CI = dyn_cast<FCmpInst>(&I))
303 return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
304 SO->getName()+".cmp");
305 llvm_unreachable("Unknown binary instruction type!");
308 // FoldOpIntoSelect - Given an instruction with a select as one operand and a
309 // constant as the other operand, try to fold the binary operator into the
310 // select arguments. This also works for Cast instructions, which obviously do
311 // not have a second operand.
312 Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
313 // Don't modify shared select instructions
314 if (!SI->hasOneUse()) return 0;
315 Value *TV = SI->getOperand(1);
316 Value *FV = SI->getOperand(2);
318 if (isa<Constant>(TV) || isa<Constant>(FV)) {
319 // Bool selects with constant operands can be folded to logical ops.
320 if (SI->getType()->isIntegerTy(1)) return 0;
322 Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
323 Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
325 return SelectInst::Create(SI->getCondition(), SelectTrueVal,
332 /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
333 /// has a PHI node as operand #0, see if we can fold the instruction into the
334 /// PHI (which is only possible if all operands to the PHI are constants).
336 /// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms
337 /// that would normally be unprofitable because they strongly encourage jump
339 Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
340 bool AllowAggressive) {
341 AllowAggressive = false;
342 PHINode *PN = cast<PHINode>(I.getOperand(0));
343 unsigned NumPHIValues = PN->getNumIncomingValues();
344 if (NumPHIValues == 0 ||
345 // We normally only transform phis with a single use, unless we're trying
346 // hard to make jump threading happen.
347 (!PN->hasOneUse() && !AllowAggressive))
351 // Check to see if all of the operands of the PHI are simple constants
352 // (constantint/constantfp/undef). If there is one non-constant value,
353 // remember the BB it is in. If there is more than one or if *it* is a PHI,
354 // bail out. We don't do arbitrary constant expressions here because moving
355 // their computation can be expensive without a cost model.
356 BasicBlock *NonConstBB = 0;
357 for (unsigned i = 0; i != NumPHIValues; ++i)
358 if (!isa<Constant>(PN->getIncomingValue(i)) ||
359 isa<ConstantExpr>(PN->getIncomingValue(i))) {
360 if (NonConstBB) return 0; // More than one non-const value.
361 if (isa<PHINode>(PN->getIncomingValue(i))) return 0; // Itself a phi.
362 NonConstBB = PN->getIncomingBlock(i);
364 // If the incoming non-constant value is in I's block, we have an infinite
366 if (NonConstBB == I.getParent())
370 // If there is exactly one non-constant value, we can insert a copy of the
371 // operation in that block. However, if this is a critical edge, we would be
372 // inserting the computation one some other paths (e.g. inside a loop). Only
373 // do this if the pred block is unconditionally branching into the phi block.
374 if (NonConstBB != 0 && !AllowAggressive) {
375 BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
376 if (!BI || !BI->isUnconditional()) return 0;
379 // Okay, we can do the transformation: create the new PHI node.
380 PHINode *NewPN = PHINode::Create(I.getType(), "");
381 NewPN->reserveOperandSpace(PN->getNumOperands()/2);
382 InsertNewInstBefore(NewPN, *PN);
385 // Next, add all of the operands to the PHI.
386 if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
387 // We only currently try to fold the condition of a select when it is a phi,
388 // not the true/false values.
389 Value *TrueV = SI->getTrueValue();
390 Value *FalseV = SI->getFalseValue();
391 BasicBlock *PhiTransBB = PN->getParent();
392 for (unsigned i = 0; i != NumPHIValues; ++i) {
393 BasicBlock *ThisBB = PN->getIncomingBlock(i);
394 Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
395 Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
397 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
398 InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
400 assert(PN->getIncomingBlock(i) == NonConstBB);
401 InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred,
403 "phitmp", NonConstBB->getTerminator());
404 Worklist.Add(cast<Instruction>(InV));
406 NewPN->addIncoming(InV, ThisBB);
408 } else if (I.getNumOperands() == 2) {
409 Constant *C = cast<Constant>(I.getOperand(1));
410 for (unsigned i = 0; i != NumPHIValues; ++i) {
412 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
413 if (CmpInst *CI = dyn_cast<CmpInst>(&I))
414 InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
416 InV = ConstantExpr::get(I.getOpcode(), InC, C);
418 assert(PN->getIncomingBlock(i) == NonConstBB);
419 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
420 InV = BinaryOperator::Create(BO->getOpcode(),
421 PN->getIncomingValue(i), C, "phitmp",
422 NonConstBB->getTerminator());
423 else if (CmpInst *CI = dyn_cast<CmpInst>(&I))
424 InV = CmpInst::Create(CI->getOpcode(),
426 PN->getIncomingValue(i), C, "phitmp",
427 NonConstBB->getTerminator());
429 llvm_unreachable("Unknown binop!");
431 Worklist.Add(cast<Instruction>(InV));
433 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
436 CastInst *CI = cast<CastInst>(&I);
437 const Type *RetTy = CI->getType();
438 for (unsigned i = 0; i != NumPHIValues; ++i) {
440 if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
441 InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
443 assert(PN->getIncomingBlock(i) == NonConstBB);
444 InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i),
445 I.getType(), "phitmp",
446 NonConstBB->getTerminator());
447 Worklist.Add(cast<Instruction>(InV));
449 NewPN->addIncoming(InV, PN->getIncomingBlock(i));
452 return ReplaceInstUsesWith(I, NewPN);
455 /// FindElementAtOffset - Given a type and a constant offset, determine whether
456 /// or not there is a sequence of GEP indices into the type that will land us at
457 /// the specified offset. If so, fill them into NewIndices and return the
458 /// resultant element type, otherwise return null.
459 const Type *InstCombiner::FindElementAtOffset(const Type *Ty, int64_t Offset,
460 SmallVectorImpl<Value*> &NewIndices) {
462 if (!Ty->isSized()) return 0;
464 // Start with the index over the outer type. Note that the type size
465 // might be zero (even if the offset isn't zero) if the indexed type
466 // is something like [0 x {int, int}]
467 const Type *IntPtrTy = TD->getIntPtrType(Ty->getContext());
468 int64_t FirstIdx = 0;
469 if (int64_t TySize = TD->getTypeAllocSize(Ty)) {
470 FirstIdx = Offset/TySize;
471 Offset -= FirstIdx*TySize;
473 // Handle hosts where % returns negative instead of values [0..TySize).
479 assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
482 NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
484 // Index into the types. If we fail, set OrigBase to null.
486 // Indexing into tail padding between struct/array elements.
487 if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty))
490 if (const StructType *STy = dyn_cast<StructType>(Ty)) {
491 const StructLayout *SL = TD->getStructLayout(STy);
492 assert(Offset < (int64_t)SL->getSizeInBytes() &&
493 "Offset must stay within the indexed type");
495 unsigned Elt = SL->getElementContainingOffset(Offset);
496 NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
499 Offset -= SL->getElementOffset(Elt);
500 Ty = STy->getElementType(Elt);
501 } else if (const ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
502 uint64_t EltSize = TD->getTypeAllocSize(AT->getElementType());
503 assert(EltSize && "Cannot index into a zero-sized array");
504 NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
506 Ty = AT->getElementType();
508 // Otherwise, we can't index into the middle of this atomic type, bail.
518 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
519 SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
521 if (Value *V = SimplifyGEPInst(&Ops[0], Ops.size(), TD))
522 return ReplaceInstUsesWith(GEP, V);
524 Value *PtrOp = GEP.getOperand(0);
526 if (isa<UndefValue>(GEP.getOperand(0)))
527 return ReplaceInstUsesWith(GEP, UndefValue::get(GEP.getType()));
529 // Eliminate unneeded casts for indices.
531 bool MadeChange = false;
532 unsigned PtrSize = TD->getPointerSizeInBits();
534 gep_type_iterator GTI = gep_type_begin(GEP);
535 for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end();
536 I != E; ++I, ++GTI) {
537 if (!isa<SequentialType>(*GTI)) continue;
539 // If we are using a wider index than needed for this platform, shrink it
540 // to what we need. If narrower, sign-extend it to what we need. This
541 // explicit cast can make subsequent optimizations more obvious.
542 unsigned OpBits = cast<IntegerType>((*I)->getType())->getBitWidth();
543 if (OpBits == PtrSize)
546 *I = Builder->CreateIntCast(*I, TD->getIntPtrType(GEP.getContext()),true);
549 if (MadeChange) return &GEP;
552 // Combine Indices - If the source pointer to this getelementptr instruction
553 // is a getelementptr instruction, combine the indices of the two
554 // getelementptr instructions into a single instruction.
556 if (GEPOperator *Src = dyn_cast<GEPOperator>(PtrOp)) {
557 // Note that if our source is a gep chain itself that we wait for that
558 // chain to be resolved before we perform this transformation. This
559 // avoids us creating a TON of code in some cases.
561 if (GetElementPtrInst *SrcGEP =
562 dyn_cast<GetElementPtrInst>(Src->getOperand(0)))
563 if (SrcGEP->getNumOperands() == 2)
564 return 0; // Wait until our source is folded to completion.
566 SmallVector<Value*, 8> Indices;
568 // Find out whether the last index in the source GEP is a sequential idx.
569 bool EndsWithSequential = false;
570 for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
572 EndsWithSequential = !(*I)->isStructTy();
574 // Can we combine the two pointer arithmetics offsets?
575 if (EndsWithSequential) {
576 // Replace: gep (gep %P, long B), long A, ...
577 // With: T = long A+B; gep %P, T, ...
580 Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
581 Value *GO1 = GEP.getOperand(1);
582 if (SO1 == Constant::getNullValue(SO1->getType())) {
584 } else if (GO1 == Constant::getNullValue(GO1->getType())) {
587 // If they aren't the same type, then the input hasn't been processed
588 // by the loop above yet (which canonicalizes sequential index types to
589 // intptr_t). Just avoid transforming this until the input has been
591 if (SO1->getType() != GO1->getType())
593 Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
596 // Update the GEP in place if possible.
597 if (Src->getNumOperands() == 2) {
598 GEP.setOperand(0, Src->getOperand(0));
599 GEP.setOperand(1, Sum);
602 Indices.append(Src->op_begin()+1, Src->op_end()-1);
603 Indices.push_back(Sum);
604 Indices.append(GEP.op_begin()+2, GEP.op_end());
605 } else if (isa<Constant>(*GEP.idx_begin()) &&
606 cast<Constant>(*GEP.idx_begin())->isNullValue() &&
607 Src->getNumOperands() != 1) {
608 // Otherwise we can do the fold if the first index of the GEP is a zero
609 Indices.append(Src->op_begin()+1, Src->op_end());
610 Indices.append(GEP.idx_begin()+1, GEP.idx_end());
613 if (!Indices.empty())
614 return (GEP.isInBounds() && Src->isInBounds()) ?
615 GetElementPtrInst::CreateInBounds(Src->getOperand(0), Indices.begin(),
616 Indices.end(), GEP.getName()) :
617 GetElementPtrInst::Create(Src->getOperand(0), Indices.begin(),
618 Indices.end(), GEP.getName());
621 // Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
622 Value *StrippedPtr = PtrOp->stripPointerCasts();
623 if (StrippedPtr != PtrOp) {
624 const PointerType *StrippedPtrTy =cast<PointerType>(StrippedPtr->getType());
626 bool HasZeroPointerIndex = false;
627 if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
628 HasZeroPointerIndex = C->isZero();
630 // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
631 // into : GEP [10 x i8]* X, i32 0, ...
633 // Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
634 // into : GEP i8* X, ...
636 // This occurs when the program declares an array extern like "int X[];"
637 if (HasZeroPointerIndex) {
638 const PointerType *CPTy = cast<PointerType>(PtrOp->getType());
639 if (const ArrayType *CATy =
640 dyn_cast<ArrayType>(CPTy->getElementType())) {
641 // GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
642 if (CATy->getElementType() == StrippedPtrTy->getElementType()) {
644 SmallVector<Value*, 8> Idx(GEP.idx_begin()+1, GEP.idx_end());
645 GetElementPtrInst *Res =
646 GetElementPtrInst::Create(StrippedPtr, Idx.begin(),
647 Idx.end(), GEP.getName());
648 Res->setIsInBounds(GEP.isInBounds());
652 if (const ArrayType *XATy =
653 dyn_cast<ArrayType>(StrippedPtrTy->getElementType())){
654 // GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
655 if (CATy->getElementType() == XATy->getElementType()) {
656 // -> GEP [10 x i8]* X, i32 0, ...
657 // At this point, we know that the cast source type is a pointer
658 // to an array of the same type as the destination pointer
659 // array. Because the array type is never stepped over (there
660 // is a leading zero) we can fold the cast into this GEP.
661 GEP.setOperand(0, StrippedPtr);
666 } else if (GEP.getNumOperands() == 2) {
667 // Transform things like:
668 // %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
669 // into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
670 const Type *SrcElTy = StrippedPtrTy->getElementType();
671 const Type *ResElTy=cast<PointerType>(PtrOp->getType())->getElementType();
672 if (TD && SrcElTy->isArrayTy() &&
673 TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType()) ==
674 TD->getTypeAllocSize(ResElTy)) {
676 Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
677 Idx[1] = GEP.getOperand(1);
678 Value *NewGEP = GEP.isInBounds() ?
679 Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()) :
680 Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
681 // V and GEP are both pointer types --> BitCast
682 return new BitCastInst(NewGEP, GEP.getType());
685 // Transform things like:
686 // getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
687 // (where tmp = 8*tmp2) into:
688 // getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
690 if (TD && SrcElTy->isArrayTy() && ResElTy->isIntegerTy(8)) {
691 uint64_t ArrayEltSize =
692 TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType());
694 // Check to see if "tmp" is a scale by a multiple of ArrayEltSize. We
695 // allow either a mul, shift, or constant here.
697 ConstantInt *Scale = 0;
698 if (ArrayEltSize == 1) {
699 NewIdx = GEP.getOperand(1);
700 Scale = ConstantInt::get(cast<IntegerType>(NewIdx->getType()), 1);
701 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP.getOperand(1))) {
702 NewIdx = ConstantInt::get(CI->getType(), 1);
704 } else if (Instruction *Inst =dyn_cast<Instruction>(GEP.getOperand(1))){
705 if (Inst->getOpcode() == Instruction::Shl &&
706 isa<ConstantInt>(Inst->getOperand(1))) {
707 ConstantInt *ShAmt = cast<ConstantInt>(Inst->getOperand(1));
708 uint32_t ShAmtVal = ShAmt->getLimitedValue(64);
709 Scale = ConstantInt::get(cast<IntegerType>(Inst->getType()),
711 NewIdx = Inst->getOperand(0);
712 } else if (Inst->getOpcode() == Instruction::Mul &&
713 isa<ConstantInt>(Inst->getOperand(1))) {
714 Scale = cast<ConstantInt>(Inst->getOperand(1));
715 NewIdx = Inst->getOperand(0);
719 // If the index will be to exactly the right offset with the scale taken
720 // out, perform the transformation. Note, we don't know whether Scale is
721 // signed or not. We'll use unsigned version of division/modulo
722 // operation after making sure Scale doesn't have the sign bit set.
723 if (ArrayEltSize && Scale && Scale->getSExtValue() >= 0LL &&
724 Scale->getZExtValue() % ArrayEltSize == 0) {
725 Scale = ConstantInt::get(Scale->getType(),
726 Scale->getZExtValue() / ArrayEltSize);
727 if (Scale->getZExtValue() != 1) {
728 Constant *C = ConstantExpr::getIntegerCast(Scale, NewIdx->getType(),
730 NewIdx = Builder->CreateMul(NewIdx, C, "idxscale");
733 // Insert the new GEP instruction.
735 Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
737 Value *NewGEP = GEP.isInBounds() ?
738 Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2,GEP.getName()):
739 Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
740 // The NewGEP must be pointer typed, so must the old one -> BitCast
741 return new BitCastInst(NewGEP, GEP.getType());
747 /// See if we can simplify:
748 /// X = bitcast A* to B*
749 /// Y = gep X, <...constant indices...>
750 /// into a gep of the original struct. This is important for SROA and alias
751 /// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
752 if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
754 !isa<BitCastInst>(BCI->getOperand(0)) && GEP.hasAllConstantIndices()) {
755 // Determine how much the GEP moves the pointer. We are guaranteed to get
756 // a constant back from EmitGEPOffset.
757 ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(&GEP));
758 int64_t Offset = OffsetV->getSExtValue();
760 // If this GEP instruction doesn't move the pointer, just replace the GEP
761 // with a bitcast of the real input to the dest type.
763 // If the bitcast is of an allocation, and the allocation will be
764 // converted to match the type of the cast, don't touch this.
765 if (isa<AllocaInst>(BCI->getOperand(0)) ||
766 isMalloc(BCI->getOperand(0))) {
767 // See if the bitcast simplifies, if so, don't nuke this GEP yet.
768 if (Instruction *I = visitBitCast(*BCI)) {
771 BCI->getParent()->getInstList().insert(BCI, I);
772 ReplaceInstUsesWith(*BCI, I);
777 return new BitCastInst(BCI->getOperand(0), GEP.getType());
780 // Otherwise, if the offset is non-zero, we need to find out if there is a
781 // field at Offset in 'A's type. If so, we can pull the cast through the
783 SmallVector<Value*, 8> NewIndices;
785 cast<PointerType>(BCI->getOperand(0)->getType())->getElementType();
786 if (FindElementAtOffset(InTy, Offset, NewIndices)) {
787 Value *NGEP = GEP.isInBounds() ?
788 Builder->CreateInBoundsGEP(BCI->getOperand(0), NewIndices.begin(),
790 Builder->CreateGEP(BCI->getOperand(0), NewIndices.begin(),
793 if (NGEP->getType() == GEP.getType())
794 return ReplaceInstUsesWith(GEP, NGEP);
795 NGEP->takeName(&GEP);
796 return new BitCastInst(NGEP, GEP.getType());
806 static bool IsOnlyNullComparedAndFreed(const Value &V) {
807 for (Value::const_use_iterator UI = V.use_begin(), UE = V.use_end();
812 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(U))
813 if (ICI->isEquality() && isa<ConstantPointerNull>(ICI->getOperand(1)))
820 Instruction *InstCombiner::visitMalloc(Instruction &MI) {
821 // If we have a malloc call which is only used in any amount of comparisons
822 // to null and free calls, delete the calls and replace the comparisons with
823 // true or false as appropriate.
824 if (IsOnlyNullComparedAndFreed(MI)) {
825 for (Value::use_iterator UI = MI.use_begin(), UE = MI.use_end();
827 // We can assume that every remaining use is a free call or an icmp eq/ne
828 // to null, so the cast is safe.
829 Instruction *I = cast<Instruction>(*UI);
831 // Early increment here, as we're about to get rid of the user.
835 EraseInstFromFunction(*cast<CallInst>(I));
838 // Again, the cast is safe.
839 ICmpInst *C = cast<ICmpInst>(I);
840 ReplaceInstUsesWith(*C, ConstantInt::get(Type::getInt1Ty(C->getContext()),
841 C->isFalseWhenEqual()));
842 EraseInstFromFunction(*C);
844 return EraseInstFromFunction(MI);
851 Instruction *InstCombiner::visitFree(CallInst &FI) {
852 Value *Op = FI.getArgOperand(0);
854 // free undef -> unreachable.
855 if (isa<UndefValue>(Op)) {
856 // Insert a new store to null because we cannot modify the CFG here.
857 new StoreInst(ConstantInt::getTrue(FI.getContext()),
858 UndefValue::get(Type::getInt1PtrTy(FI.getContext())), &FI);
859 return EraseInstFromFunction(FI);
862 // If we have 'free null' delete the instruction. This can happen in stl code
863 // when lots of inlining happens.
864 if (isa<ConstantPointerNull>(Op))
865 return EraseInstFromFunction(FI);
872 Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
873 // Change br (not X), label True, label False to: br X, label False, True
875 BasicBlock *TrueDest;
876 BasicBlock *FalseDest;
877 if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) &&
879 // Swap Destinations and condition...
881 BI.setSuccessor(0, FalseDest);
882 BI.setSuccessor(1, TrueDest);
886 // Cannonicalize fcmp_one -> fcmp_oeq
887 FCmpInst::Predicate FPred; Value *Y;
888 if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)),
889 TrueDest, FalseDest)) &&
890 BI.getCondition()->hasOneUse())
891 if (FPred == FCmpInst::FCMP_ONE || FPred == FCmpInst::FCMP_OLE ||
892 FPred == FCmpInst::FCMP_OGE) {
893 FCmpInst *Cond = cast<FCmpInst>(BI.getCondition());
894 Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
896 // Swap Destinations and condition.
897 BI.setSuccessor(0, FalseDest);
898 BI.setSuccessor(1, TrueDest);
903 // Cannonicalize icmp_ne -> icmp_eq
904 ICmpInst::Predicate IPred;
905 if (match(&BI, m_Br(m_ICmp(IPred, m_Value(X), m_Value(Y)),
906 TrueDest, FalseDest)) &&
907 BI.getCondition()->hasOneUse())
908 if (IPred == ICmpInst::ICMP_NE || IPred == ICmpInst::ICMP_ULE ||
909 IPred == ICmpInst::ICMP_SLE || IPred == ICmpInst::ICMP_UGE ||
910 IPred == ICmpInst::ICMP_SGE) {
911 ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
912 Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
913 // Swap Destinations and condition.
914 BI.setSuccessor(0, FalseDest);
915 BI.setSuccessor(1, TrueDest);
923 Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
924 Value *Cond = SI.getCondition();
925 if (Instruction *I = dyn_cast<Instruction>(Cond)) {
926 if (I->getOpcode() == Instruction::Add)
927 if (ConstantInt *AddRHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
928 // change 'switch (X+4) case 1:' into 'switch (X) case -3'
929 for (unsigned i = 2, e = SI.getNumOperands(); i != e; i += 2)
931 ConstantExpr::getSub(cast<Constant>(SI.getOperand(i)),
933 SI.setOperand(0, I->getOperand(0));
941 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
942 Value *Agg = EV.getAggregateOperand();
944 if (!EV.hasIndices())
945 return ReplaceInstUsesWith(EV, Agg);
947 if (Constant *C = dyn_cast<Constant>(Agg)) {
948 if (isa<UndefValue>(C))
949 return ReplaceInstUsesWith(EV, UndefValue::get(EV.getType()));
951 if (isa<ConstantAggregateZero>(C))
952 return ReplaceInstUsesWith(EV, Constant::getNullValue(EV.getType()));
954 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
955 // Extract the element indexed by the first index out of the constant
956 Value *V = C->getOperand(*EV.idx_begin());
957 if (EV.getNumIndices() > 1)
958 // Extract the remaining indices out of the constant indexed by the
960 return ExtractValueInst::Create(V, EV.idx_begin() + 1, EV.idx_end());
962 return ReplaceInstUsesWith(EV, V);
964 return 0; // Can't handle other constants
966 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
967 // We're extracting from an insertvalue instruction, compare the indices
968 const unsigned *exti, *exte, *insi, *inse;
969 for (exti = EV.idx_begin(), insi = IV->idx_begin(),
970 exte = EV.idx_end(), inse = IV->idx_end();
971 exti != exte && insi != inse;
974 // The insert and extract both reference distinctly different elements.
975 // This means the extract is not influenced by the insert, and we can
976 // replace the aggregate operand of the extract with the aggregate
977 // operand of the insert. i.e., replace
978 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
979 // %E = extractvalue { i32, { i32 } } %I, 0
981 // %E = extractvalue { i32, { i32 } } %A, 0
982 return ExtractValueInst::Create(IV->getAggregateOperand(),
983 EV.idx_begin(), EV.idx_end());
985 if (exti == exte && insi == inse)
986 // Both iterators are at the end: Index lists are identical. Replace
987 // %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
988 // %C = extractvalue { i32, { i32 } } %B, 1, 0
990 return ReplaceInstUsesWith(EV, IV->getInsertedValueOperand());
992 // The extract list is a prefix of the insert list. i.e. replace
993 // %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
994 // %E = extractvalue { i32, { i32 } } %I, 1
996 // %X = extractvalue { i32, { i32 } } %A, 1
997 // %E = insertvalue { i32 } %X, i32 42, 0
998 // by switching the order of the insert and extract (though the
999 // insertvalue should be left in, since it may have other uses).
1000 Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(),
1001 EV.idx_begin(), EV.idx_end());
1002 return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
1006 // The insert list is a prefix of the extract list
1007 // We can simply remove the common indices from the extract and make it
1008 // operate on the inserted value instead of the insertvalue result.
1010 // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
1011 // %E = extractvalue { i32, { i32 } } %I, 1, 0
1013 // %E extractvalue { i32 } { i32 42 }, 0
1014 return ExtractValueInst::Create(IV->getInsertedValueOperand(),
1017 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
1018 // We're extracting from an intrinsic, see if we're the only user, which
1019 // allows us to simplify multiple result intrinsics to simpler things that
1020 // just get one value.
1021 if (II->hasOneUse()) {
1022 // Check if we're grabbing the overflow bit or the result of a 'with
1023 // overflow' intrinsic. If it's the latter we can remove the intrinsic
1024 // and replace it with a traditional binary instruction.
1025 switch (II->getIntrinsicID()) {
1026 case Intrinsic::uadd_with_overflow:
1027 case Intrinsic::sadd_with_overflow:
1028 if (*EV.idx_begin() == 0) { // Normal result.
1029 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1030 II->replaceAllUsesWith(UndefValue::get(II->getType()));
1031 EraseInstFromFunction(*II);
1032 return BinaryOperator::CreateAdd(LHS, RHS);
1035 case Intrinsic::usub_with_overflow:
1036 case Intrinsic::ssub_with_overflow:
1037 if (*EV.idx_begin() == 0) { // Normal result.
1038 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1039 II->replaceAllUsesWith(UndefValue::get(II->getType()));
1040 EraseInstFromFunction(*II);
1041 return BinaryOperator::CreateSub(LHS, RHS);
1044 case Intrinsic::umul_with_overflow:
1045 case Intrinsic::smul_with_overflow:
1046 if (*EV.idx_begin() == 0) { // Normal result.
1047 Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
1048 II->replaceAllUsesWith(UndefValue::get(II->getType()));
1049 EraseInstFromFunction(*II);
1050 return BinaryOperator::CreateMul(LHS, RHS);
1058 // Can't simplify extracts from other values. Note that nested extracts are
1059 // already simplified implicitely by the above (extract ( extract (insert) )
1060 // will be translated into extract ( insert ( extract ) ) first and then just
1061 // the value inserted, if appropriate).
1068 /// TryToSinkInstruction - Try to move the specified instruction from its
1069 /// current block into the beginning of DestBlock, which can only happen if it's
1070 /// safe to move the instruction past all of the instructions between it and the
1071 /// end of its block.
1072 static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
1073 assert(I->hasOneUse() && "Invariants didn't hold!");
1075 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1076 if (isa<PHINode>(I) || I->mayHaveSideEffects() || isa<TerminatorInst>(I))
1079 // Do not sink alloca instructions out of the entry block.
1080 if (isa<AllocaInst>(I) && I->getParent() ==
1081 &DestBlock->getParent()->getEntryBlock())
1084 // We can only sink load instructions if there is nothing between the load and
1085 // the end of block that could change the value.
1086 if (I->mayReadFromMemory()) {
1087 for (BasicBlock::iterator Scan = I, E = I->getParent()->end();
1089 if (Scan->mayWriteToMemory())
1093 BasicBlock::iterator InsertPos = DestBlock->getFirstNonPHI();
1095 I->moveBefore(InsertPos);
1101 /// AddReachableCodeToWorklist - Walk the function in depth-first order, adding
1102 /// all reachable code to the worklist.
1104 /// This has a couple of tricks to make the code faster and more powerful. In
1105 /// particular, we constant fold and DCE instructions as we go, to avoid adding
1106 /// them to the worklist (this significantly speeds up instcombine on code where
1107 /// many instructions are dead or constant). Additionally, if we find a branch
1108 /// whose condition is a known constant, we only visit the reachable successors.
1110 static bool AddReachableCodeToWorklist(BasicBlock *BB,
1111 SmallPtrSet<BasicBlock*, 64> &Visited,
1113 const TargetData *TD) {
1114 bool MadeIRChange = false;
1115 SmallVector<BasicBlock*, 256> Worklist;
1116 Worklist.push_back(BB);
1118 SmallVector<Instruction*, 128> InstrsForInstCombineWorklist;
1119 SmallPtrSet<ConstantExpr*, 64> FoldedConstants;
1122 BB = Worklist.pop_back_val();
1124 // We have now visited this block! If we've already been here, ignore it.
1125 if (!Visited.insert(BB)) continue;
1127 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) {
1128 Instruction *Inst = BBI++;
1130 // DCE instruction if trivially dead.
1131 if (isInstructionTriviallyDead(Inst)) {
1133 DEBUG(errs() << "IC: DCE: " << *Inst << '\n');
1134 Inst->eraseFromParent();
1138 // ConstantProp instruction if trivially constant.
1139 if (!Inst->use_empty() && isa<Constant>(Inst->getOperand(0)))
1140 if (Constant *C = ConstantFoldInstruction(Inst, TD)) {
1141 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: "
1143 Inst->replaceAllUsesWith(C);
1145 Inst->eraseFromParent();
1150 // See if we can constant fold its operands.
1151 for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end();
1153 ConstantExpr *CE = dyn_cast<ConstantExpr>(i);
1154 if (CE == 0) continue;
1156 // If we already folded this constant, don't try again.
1157 if (!FoldedConstants.insert(CE))
1160 Constant *NewC = ConstantFoldConstantExpression(CE, TD);
1161 if (NewC && NewC != CE) {
1163 MadeIRChange = true;
1168 InstrsForInstCombineWorklist.push_back(Inst);
1171 // Recursively visit successors. If this is a branch or switch on a
1172 // constant, only visit the reachable successor.
1173 TerminatorInst *TI = BB->getTerminator();
1174 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1175 if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
1176 bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
1177 BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
1178 Worklist.push_back(ReachableBB);
1181 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1182 if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
1183 // See if this is an explicit destination.
1184 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
1185 if (SI->getCaseValue(i) == Cond) {
1186 BasicBlock *ReachableBB = SI->getSuccessor(i);
1187 Worklist.push_back(ReachableBB);
1191 // Otherwise it is the default destination.
1192 Worklist.push_back(SI->getSuccessor(0));
1197 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
1198 Worklist.push_back(TI->getSuccessor(i));
1199 } while (!Worklist.empty());
1201 // Once we've found all of the instructions to add to instcombine's worklist,
1202 // add them in reverse order. This way instcombine will visit from the top
1203 // of the function down. This jives well with the way that it adds all uses
1204 // of instructions to the worklist after doing a transformation, thus avoiding
1205 // some N^2 behavior in pathological cases.
1206 IC.Worklist.AddInitialGroup(&InstrsForInstCombineWorklist[0],
1207 InstrsForInstCombineWorklist.size());
1209 return MadeIRChange;
1212 bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {
1213 MadeIRChange = false;
1215 DEBUG(errs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on "
1216 << F.getNameStr() << "\n");
1219 // Do a depth-first traversal of the function, populate the worklist with
1220 // the reachable instructions. Ignore blocks that are not reachable. Keep
1221 // track of which blocks we visit.
1222 SmallPtrSet<BasicBlock*, 64> Visited;
1223 MadeIRChange |= AddReachableCodeToWorklist(F.begin(), Visited, *this, TD);
1225 // Do a quick scan over the function. If we find any blocks that are
1226 // unreachable, remove any instructions inside of them. This prevents
1227 // the instcombine code from having to deal with some bad special cases.
1228 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1229 if (!Visited.count(BB)) {
1230 Instruction *Term = BB->getTerminator();
1231 while (Term != BB->begin()) { // Remove instrs bottom-up
1232 BasicBlock::iterator I = Term; --I;
1234 DEBUG(errs() << "IC: DCE: " << *I << '\n');
1235 // A debug intrinsic shouldn't force another iteration if we weren't
1236 // going to do one without it.
1237 if (!isa<DbgInfoIntrinsic>(I)) {
1239 MadeIRChange = true;
1242 // If I is not void type then replaceAllUsesWith undef.
1243 // This allows ValueHandlers and custom metadata to adjust itself.
1244 if (!I->getType()->isVoidTy())
1245 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1246 I->eraseFromParent();
1251 while (!Worklist.isEmpty()) {
1252 Instruction *I = Worklist.RemoveOne();
1253 if (I == 0) continue; // skip null values.
1255 // Check to see if we can DCE the instruction.
1256 if (isInstructionTriviallyDead(I)) {
1257 DEBUG(errs() << "IC: DCE: " << *I << '\n');
1258 EraseInstFromFunction(*I);
1260 MadeIRChange = true;
1264 // Instruction isn't dead, see if we can constant propagate it.
1265 if (!I->use_empty() && isa<Constant>(I->getOperand(0)))
1266 if (Constant *C = ConstantFoldInstruction(I, TD)) {
1267 DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *I << '\n');
1269 // Add operands to the worklist.
1270 ReplaceInstUsesWith(*I, C);
1272 EraseInstFromFunction(*I);
1273 MadeIRChange = true;
1277 // See if we can trivially sink this instruction to a successor basic block.
1278 if (I->hasOneUse()) {
1279 BasicBlock *BB = I->getParent();
1280 Instruction *UserInst = cast<Instruction>(I->use_back());
1281 BasicBlock *UserParent;
1283 // Get the block the use occurs in.
1284 if (PHINode *PN = dyn_cast<PHINode>(UserInst))
1285 UserParent = PN->getIncomingBlock(I->use_begin().getUse());
1287 UserParent = UserInst->getParent();
1289 if (UserParent != BB) {
1290 bool UserIsSuccessor = false;
1291 // See if the user is one of our successors.
1292 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1293 if (*SI == UserParent) {
1294 UserIsSuccessor = true;
1298 // If the user is one of our immediate successors, and if that successor
1299 // only has us as a predecessors (we'd have to split the critical edge
1300 // otherwise), we can keep going.
1301 if (UserIsSuccessor && UserParent->getSinglePredecessor())
1302 // Okay, the CFG is simple enough, try to sink this instruction.
1303 MadeIRChange |= TryToSinkInstruction(I, UserParent);
1307 // Now that we have an instruction, try combining it to simplify it.
1308 Builder->SetInsertPoint(I->getParent(), I);
1313 DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
1314 DEBUG(errs() << "IC: Visiting: " << OrigI << '\n');
1316 if (Instruction *Result = visit(*I)) {
1318 // Should we replace the old instruction with a new one?
1320 DEBUG(errs() << "IC: Old = " << *I << '\n'
1321 << " New = " << *Result << '\n');
1323 // Everything uses the new instruction now.
1324 I->replaceAllUsesWith(Result);
1326 // Push the new instruction and any users onto the worklist.
1327 Worklist.Add(Result);
1328 Worklist.AddUsersToWorkList(*Result);
1330 // Move the name to the new instruction first.
1331 Result->takeName(I);
1333 // Insert the new instruction into the basic block...
1334 BasicBlock *InstParent = I->getParent();
1335 BasicBlock::iterator InsertPos = I;
1337 if (!isa<PHINode>(Result)) // If combining a PHI, don't insert
1338 while (isa<PHINode>(InsertPos)) // middle of a block of PHIs.
1341 InstParent->getInstList().insert(InsertPos, Result);
1343 EraseInstFromFunction(*I);
1346 DEBUG(errs() << "IC: Mod = " << OrigI << '\n'
1347 << " New = " << *I << '\n');
1350 // If the instruction was modified, it's possible that it is now dead.
1351 // if so, remove it.
1352 if (isInstructionTriviallyDead(I)) {
1353 EraseInstFromFunction(*I);
1356 Worklist.AddUsersToWorkList(*I);
1359 MadeIRChange = true;
1364 return MadeIRChange;
1368 bool InstCombiner::runOnFunction(Function &F) {
1369 MustPreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
1370 TD = getAnalysisIfAvailable<TargetData>();
1373 /// Builder - This is an IRBuilder that automatically inserts new
1374 /// instructions into the worklist when they are created.
1375 IRBuilder<true, TargetFolder, InstCombineIRInserter>
1376 TheBuilder(F.getContext(), TargetFolder(TD),
1377 InstCombineIRInserter(Worklist));
1378 Builder = &TheBuilder;
1380 bool EverMadeChange = false;
1382 // Iterate while there is work to do.
1383 unsigned Iteration = 0;
1384 while (DoOneIteration(F, Iteration++))
1385 EverMadeChange = true;
1388 return EverMadeChange;
1391 FunctionPass *llvm::createInstructionCombiningPass() {
1392 return new InstCombiner();