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Teach instsimplify to be more aggressive when analyzing comparisons of pointers

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by using llvm::isIdentifiedObject. Also teach it to handle GEPs that have
the same base pointer and constant operands. Fixes PR11238!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151449 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2012-02-25 19:07:42 +00:00
parent 55f4ab84e5
commit 1e4e1c768b
3 changed files with 86 additions and 13 deletions
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51
lib/Analysis/InstructionSimplify.cpp
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@ -21,6 +21,7 @@
#include "llvm/Operator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
@ -1608,26 +1609,37 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
// icmp <alloca*>, <global/alloca*/null> - Different stack variables have
// icmp <object*>, <object*/null> - Different identified objects have
// different addresses, and what's more the address of a stack variable is
// never null or equal to the address of a global. Note that generalizing
// to the case where LHS is a global variable address or null is pointless,
// since if both LHS and RHS are constants then we already constant folded
// the compare, and if only one of them is then we moved it to RHS already.
// never equal to another argument. Note that generalizing to the case where
// LHS is a global variable address or null is pointless, since if both LHS
// and RHS are constants then we already constant folded the compare, and if
// only one of them is then we moved it to RHS already.
Value *LHSPtr = LHS->stripPointerCasts();
Value *RHSPtr = RHS->stripPointerCasts();
if (LHSPtr == RHSPtr)
return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
// Be more aggressive about stripping pointer adjustments when checking a
// comparison of an alloca address to another object. We can rip off all
// inbounds GEP operations, even if they are variable.
LHSPtr = stripPointerAdjustments(LHSPtr);
if (isa<AllocaInst>(LHSPtr)) {
if (llvm::isIdentifiedObject(LHSPtr)) {
RHSPtr = stripPointerAdjustments(RHSPtr);
if (LHSPtr != RHSPtr &&
(isa<GlobalValue>(RHSPtr) || isa<AllocaInst>(RHSPtr) ||
isa<ConstantPointerNull>(RHSPtr)))
// If both sides are different identified objects, they aren't equal unless
// they're null.
if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr) &&
(llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// Assume that the null is on the right.
if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// A local instruction (alloca or noalias call) can't alias any incoming
// argument.
if ((isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr)) ||
(isa<Instruction>(RHSPtr) && isa<Argument>(LHSPtr)))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
}
@ -2239,6 +2251,25 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
return getFalse(ITy);
}
// Simplify comparisons of GEPs.
if (GetElementPtrInst *GLHS = dyn_cast<GetElementPtrInst>(LHS)) {
if (GEPOperator *GRHS = dyn_cast<GEPOperator>(RHS)) {
if (GLHS->getPointerOperand() == GRHS->getPointerOperand() &&
GLHS->hasAllConstantIndices() && GRHS->hasAllConstantIndices()) {
// The bases are equal and the indices are constant. Build a constant
// expression GEP with the same indices and a null base pointer to see
// what constant folding can make out of it.
Constant *Null = Constant::getNullValue(GLHS->getPointerOperandType());
SmallVector<Value *, 4> IndicesLHS(GLHS->idx_begin(), GLHS->idx_end());
Constant *NewLHS = ConstantExpr::getGetElementPtr(Null, IndicesLHS);
SmallVector<Value *, 4> IndicesRHS(GRHS->idx_begin(), GRHS->idx_end());
Constant *NewRHS = ConstantExpr::getGetElementPtr(Null, IndicesRHS);
return ConstantExpr::getICmp(Pred, NewLHS, NewRHS);
}
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))