1 //===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements routines for folding instructions into simpler forms
11 // that do not require creating new instructions. For example, this does
12 // constant folding, and can handle identities like (X&0)->0.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/Analysis/ConstantFolding.h"
18 #include "llvm/Support/ValueHandle.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/Support/PatternMatch.h"
22 using namespace llvm::PatternMatch;
24 /// SimplifyAddInst - Given operands for an Add, see if we can
25 /// fold the result. If not, this returns null.
26 Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
27 const TargetData *TD) {
28 if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
29 if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
30 Constant *Ops[] = { CLHS, CRHS };
31 return ConstantFoldInstOperands(Instruction::Add, CLHS->getType(),
35 // Canonicalize the constant to the RHS.
39 if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
41 if (isa<UndefValue>(Op1C))
45 if (Op1C->isNullValue())
49 // FIXME: Could pull several more out of instcombine.
53 /// SimplifyAndInst - Given operands for an And, see if we can
54 /// fold the result. If not, this returns null.
55 Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
56 if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
57 if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
58 Constant *Ops[] = { CLHS, CRHS };
59 return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
63 // Canonicalize the constant to the RHS.
68 if (isa<UndefValue>(Op1))
69 return Constant::getNullValue(Op0->getType());
76 if (isa<ConstantAggregateZero>(Op1))
80 if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
81 if (CP->isAllOnesValue())
84 if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
89 if (Op1CI->isAllOnesValue())
93 // A & ~A = ~A & A = 0
95 if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
96 (match(Op1, m_Not(m_Value(A))) && A == Op0))
97 return Constant::getNullValue(Op0->getType());
100 if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
101 (A == Op1 || B == Op1))
105 if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
106 (A == Op0 || B == Op0))
109 // (A & B) & A -> A & B
110 if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
111 (A == Op1 || B == Op1))
114 // A & (A & B) -> A & B
115 if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
116 (A == Op0 || B == Op0))
122 /// SimplifyOrInst - Given operands for an Or, see if we can
123 /// fold the result. If not, this returns null.
124 Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
125 if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
126 if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
127 Constant *Ops[] = { CLHS, CRHS };
128 return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
132 // Canonicalize the constant to the RHS.
137 if (isa<UndefValue>(Op1))
138 return Constant::getAllOnesValue(Op0->getType());
145 if (isa<ConstantAggregateZero>(Op1))
148 // X | <-1,-1> = <-1,-1>
149 if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
150 if (CP->isAllOnesValue())
153 if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
158 if (Op1CI->isAllOnesValue())
162 // A | ~A = ~A | A = -1
164 if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
165 (match(Op1, m_Not(m_Value(A))) && A == Op0))
166 return Constant::getAllOnesValue(Op0->getType());
169 if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
170 (A == Op1 || B == Op1))
174 if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
175 (A == Op0 || B == Op0))
178 // (A | B) | A -> A | B
179 if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
180 (A == Op1 || B == Op1))
183 // A | (A | B) -> A | B
184 if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
185 (A == Op0 || B == Op0))
192 static const Type *GetCompareTy(Value *Op) {
193 return CmpInst::makeCmpResultType(Op->getType());
196 /// ThreadCmpOverSelect - In the case of a comparison with a select instruction,
197 /// try to simplify the comparison by seeing whether both branches of the select
198 /// result in the same value. Returns the common value if so, otherwise returns
200 static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
201 Value *RHS, const TargetData *TD) {
202 // Make sure the select is on the LHS.
203 if (!isa<SelectInst>(LHS)) {
205 Pred = CmpInst::getSwappedPredicate(Pred);
207 assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
208 SelectInst *SI = cast<SelectInst>(LHS);
210 // Now that we have "cmp select(cond, TV, FV), RHS", analyse it.
211 // Does "cmp TV, RHS" simplify?
212 if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD))
213 // It does! Does "cmp FV, RHS" simplify?
214 if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD))
215 // It does! If they simplified to the same value, then use it as the
216 // result of the original comparison.
222 /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
223 /// fold the result. If not, this returns null.
224 Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
225 const TargetData *TD) {
226 CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
227 assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
229 if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
230 if (Constant *CRHS = dyn_cast<Constant>(RHS))
231 return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
233 // If we have a constant, make sure it is on the RHS.
235 Pred = CmpInst::getSwappedPredicate(Pred);
238 // ITy - This is the return type of the compare we're considering.
239 const Type *ITy = GetCompareTy(LHS);
241 // icmp X, X -> true/false
242 // X icmp undef -> true/false. For example, icmp ugt %X, undef -> false
243 // because X could be 0.
244 if (LHS == RHS || isa<UndefValue>(RHS))
245 return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
247 // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
248 // addresses never equal each other! We already know that Op0 != Op1.
249 if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
250 isa<ConstantPointerNull>(LHS)) &&
251 (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
252 isa<ConstantPointerNull>(RHS)))
253 return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
255 // See if we are doing a comparison with a constant.
256 if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
257 // If we have an icmp le or icmp ge instruction, turn it into the
258 // appropriate icmp lt or icmp gt instruction. This allows us to rely on
259 // them being folded in the code below.
262 case ICmpInst::ICMP_ULE:
263 if (CI->isMaxValue(false)) // A <=u MAX -> TRUE
264 return ConstantInt::getTrue(CI->getContext());
266 case ICmpInst::ICMP_SLE:
267 if (CI->isMaxValue(true)) // A <=s MAX -> TRUE
268 return ConstantInt::getTrue(CI->getContext());
270 case ICmpInst::ICMP_UGE:
271 if (CI->isMinValue(false)) // A >=u MIN -> TRUE
272 return ConstantInt::getTrue(CI->getContext());
274 case ICmpInst::ICMP_SGE:
275 if (CI->isMinValue(true)) // A >=s MIN -> TRUE
276 return ConstantInt::getTrue(CI->getContext());
281 // If the comparison is with the result of a select instruction, check whether
282 // comparing with either branch of the select always yields the same value.
283 if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
284 if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
290 /// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
291 /// fold the result. If not, this returns null.
292 Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
293 const TargetData *TD) {
294 CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
295 assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
297 if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
298 if (Constant *CRHS = dyn_cast<Constant>(RHS))
299 return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
301 // If we have a constant, make sure it is on the RHS.
303 Pred = CmpInst::getSwappedPredicate(Pred);
306 // Fold trivial predicates.
307 if (Pred == FCmpInst::FCMP_FALSE)
308 return ConstantInt::get(GetCompareTy(LHS), 0);
309 if (Pred == FCmpInst::FCMP_TRUE)
310 return ConstantInt::get(GetCompareTy(LHS), 1);
312 if (isa<UndefValue>(RHS)) // fcmp pred X, undef -> undef
313 return UndefValue::get(GetCompareTy(LHS));
315 // fcmp x,x -> true/false. Not all compares are foldable.
317 if (CmpInst::isTrueWhenEqual(Pred))
318 return ConstantInt::get(GetCompareTy(LHS), 1);
319 if (CmpInst::isFalseWhenEqual(Pred))
320 return ConstantInt::get(GetCompareTy(LHS), 0);
323 // Handle fcmp with constant RHS
324 if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
325 // If the constant is a nan, see if we can fold the comparison based on it.
326 if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
327 if (CFP->getValueAPF().isNaN()) {
328 if (FCmpInst::isOrdered(Pred)) // True "if ordered and foo"
329 return ConstantInt::getFalse(CFP->getContext());
330 assert(FCmpInst::isUnordered(Pred) &&
331 "Comparison must be either ordered or unordered!");
332 // True if unordered.
333 return ConstantInt::getTrue(CFP->getContext());
335 // Check whether the constant is an infinity.
336 if (CFP->getValueAPF().isInfinity()) {
337 if (CFP->getValueAPF().isNegative()) {
339 case FCmpInst::FCMP_OLT:
340 // No value is ordered and less than negative infinity.
341 return ConstantInt::getFalse(CFP->getContext());
342 case FCmpInst::FCMP_UGE:
343 // All values are unordered with or at least negative infinity.
344 return ConstantInt::getTrue(CFP->getContext());
350 case FCmpInst::FCMP_OGT:
351 // No value is ordered and greater than infinity.
352 return ConstantInt::getFalse(CFP->getContext());
353 case FCmpInst::FCMP_ULE:
354 // All values are unordered with and at most infinity.
355 return ConstantInt::getTrue(CFP->getContext());
364 // If the comparison is with the result of a select instruction, check whether
365 // comparing with either branch of the select always yields the same value.
366 if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
367 if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
373 /// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
374 /// the result. If not, this returns null.
375 Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
376 const TargetData *TD) {
377 // select true, X, Y -> X
378 // select false, X, Y -> Y
379 if (ConstantInt *CB = dyn_cast<ConstantInt>(CondVal))
380 return CB->getZExtValue() ? TrueVal : FalseVal;
382 // select C, X, X -> X
383 if (TrueVal == FalseVal)
386 if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
388 if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
390 if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y
391 if (isa<Constant>(TrueVal))
402 /// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
403 /// fold the result. If not, this returns null.
404 Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
405 const TargetData *TD) {
406 // getelementptr P -> P.
411 //if (isa<UndefValue>(Ops[0]))
412 // return UndefValue::get(GEP.getType());
414 // getelementptr P, 0 -> P.
416 if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
420 // Check to see if this is constant foldable.
421 for (unsigned i = 0; i != NumOps; ++i)
422 if (!isa<Constant>(Ops[i]))
425 return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
426 (Constant *const*)Ops+1, NumOps-1);
430 //=== Helper functions for higher up the class hierarchy.
432 /// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
433 /// fold the result. If not, this returns null.
434 Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
435 const TargetData *TD) {
437 case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
438 case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD);
440 if (Constant *CLHS = dyn_cast<Constant>(LHS))
441 if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
442 Constant *COps[] = {CLHS, CRHS};
443 return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
449 /// SimplifyCmpInst - Given operands for a CmpInst, see if we can
451 Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
452 const TargetData *TD) {
453 if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
454 return SimplifyICmpInst(Predicate, LHS, RHS, TD);
455 return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
459 /// SimplifyInstruction - See if we can compute a simplified version of this
460 /// instruction. If not, this returns null.
461 Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
462 switch (I->getOpcode()) {
464 return ConstantFoldInstruction(I, TD);
465 case Instruction::Add:
466 return SimplifyAddInst(I->getOperand(0), I->getOperand(1),
467 cast<BinaryOperator>(I)->hasNoSignedWrap(),
468 cast<BinaryOperator>(I)->hasNoUnsignedWrap(), TD);
469 case Instruction::And:
470 return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD);
471 case Instruction::Or:
472 return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD);
473 case Instruction::ICmp:
474 return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
475 I->getOperand(0), I->getOperand(1), TD);
476 case Instruction::FCmp:
477 return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
478 I->getOperand(0), I->getOperand(1), TD);
479 case Instruction::Select:
480 return SimplifySelectInst(I->getOperand(0), I->getOperand(1),
481 I->getOperand(2), TD);
482 case Instruction::GetElementPtr: {
483 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
484 return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
489 /// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
490 /// delete the From instruction. In addition to a basic RAUW, this does a
491 /// recursive simplification of the newly formed instructions. This catches
492 /// things where one simplification exposes other opportunities. This only
493 /// simplifies and deletes scalar operations, it does not change the CFG.
495 void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
496 const TargetData *TD) {
497 assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
499 // FromHandle/ToHandle - This keeps a WeakVH on the from/to values so that
500 // we can know if it gets deleted out from under us or replaced in a
501 // recursive simplification.
502 WeakVH FromHandle(From);
505 while (!From->use_empty()) {
506 // Update the instruction to use the new value.
507 Use &TheUse = From->use_begin().getUse();
508 Instruction *User = cast<Instruction>(TheUse.getUser());
511 // Check to see if the instruction can be folded due to the operand
512 // replacement. For example changing (or X, Y) into (or X, -1) can replace
514 Value *SimplifiedVal;
516 // Sanity check to make sure 'User' doesn't dangle across
517 // SimplifyInstruction.
518 AssertingVH<> UserHandle(User);
520 SimplifiedVal = SimplifyInstruction(User, TD);
521 if (SimplifiedVal == 0) continue;
524 // Recursively simplify this user to the new value.
525 ReplaceAndSimplifyAllUses(User, SimplifiedVal, TD);
526 From = dyn_cast_or_null<Instruction>((Value*)FromHandle);
529 assert(ToHandle && "To value deleted by recursive simplification?");
531 // If the recursive simplification ended up revisiting and deleting
532 // 'From' then we're done.
537 // If 'From' has value handles referring to it, do a real RAUW to update them.
538 From->replaceAllUsesWith(To);
540 From->eraseFromParent();