fold comparisons of gep'd alloca points with null to false,
implementing PR12013. We now compile the testcase to:
__Z4testv: ## @_Z4testv
## BB#0: ## %_ZN4llvm15SmallVectorImplIiE9push_backERKi.exit
pushq %rbx
subq $64, %rsp
leaq 32(%rsp), %rbx
movq %rbx, (%rsp)
leaq 64(%rsp), %rax
movq %rax, 16(%rsp)
movl $1, 32(%rsp)
leaq 36(%rsp), %rax
movq %rax, 8(%rsp)
leaq (%rsp), %rdi
callq __Z1gRN4llvm11SmallVectorIiLj8EEE
movq (%rsp), %rdi
cmpq %rbx, %rdi
je LBB0_2
## BB#1:
callq _free
LBB0_2: ## %_ZN4llvm11SmallVectorIiLj8EED1Ev.exit
addq $64, %rsp
popq %rbx
ret
instead of:
__Z4testv: ## @_Z4testv
## BB#0:
pushq %rbx
subq $64, %rsp
xorl %eax, %eax
leaq (%rsp), %rbx
addq $32, %rbx
movq %rbx, (%rsp)
movq %rbx, 8(%rsp)
leaq 64(%rsp), %rcx
movq %rcx, 16(%rsp)
je LBB0_2
## BB#1:
movl $1, 32(%rsp)
movq %rbx, %rax
LBB0_2: ## %_ZN4llvm15SmallVectorImplIiE9push_backERKi.exit
addq $4, %rax
movq %rax, 8(%rsp)
leaq (%rsp), %rdi
callq __Z1gRN4llvm11SmallVectorIiLj8EEE
movq (%rsp), %rdi
cmpq %rbx, %rdi
je LBB0_4
## BB#3:
callq _free
LBB0_4: ## %_ZN4llvm11SmallVectorIiLj8EED1Ev.exit
addq $64, %rsp
popq %rbx
ret
This doesn't shrink clang noticably though.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150944 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 88a2c53..9b0ce11 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1520,6 +1520,15 @@
return 0;
}
+/// stripPointerAdjustments - This is like Value::stripPointerCasts, but also
+/// removes inbounds gep operations, regardless of their indices.
+static Value *stripPointerAdjustments(Value *V) {
+ if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
+ if (GEP->isInBounds())
+ return stripPointerAdjustments(GEP->getOperand(0)->stripPointerCasts());
+ return V;
+}
+
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
@@ -1595,10 +1604,18 @@
Value *RHSPtr = RHS->stripPointerCasts();
if (LHSPtr == RHSPtr)
return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
- if (isa<AllocaInst>(LHSPtr) && (isa<GlobalValue>(RHSPtr) ||
- isa<AllocaInst>(RHSPtr) ||
- isa<ConstantPointerNull>(RHSPtr)))
- return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(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)) {
+ RHSPtr = stripPointerAdjustments(RHSPtr);
+ if (LHSPtr != RHSPtr &&
+ (isa<GlobalValue>(RHSPtr) || isa<AllocaInst>(RHSPtr) ||
+ isa<ConstantPointerNull>(RHSPtr)))
+ return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+ }
// If we are comparing with zero then try hard since this is a common case.
if (match(RHS, m_Zero())) {