Teach instsimplify to be more aggressive when analyzing comparisons of pointers
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
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 37253f7..a6a080e 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -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 @@
}
}
- // 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 @@
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))