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Teach instsimplify how to simplify comparisons of pointers which are

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constant-offsets of a common base using the generic GEP-walking logic
I added for computing pointer differences in the same situation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153419 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-03-25 21:28:14 +00:00
parent 9d9e29b4a8
commit 58725a66c0
2 changed files with 107 additions and 1 deletions
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46
lib/Analysis/InstructionSimplify.cpp
View File

@ -1591,6 +1591,45 @@ static Value *ExtractEquivalentCondition(Value *V, CmpInst::Predicate Pred,
return 0;
}
static Constant *computePointerICmp(const TargetData &TD,
CmpInst::Predicate Pred,
Value *LHS, Value *RHS) {
// We can only fold certain predicates on pointer comparisons.
switch (Pred) {
default:
return 0;
// Equality comaprisons are easy to fold.
case CmpInst::ICMP_EQ:
case CmpInst::ICMP_NE:
break;
// We can only handle unsigned relational comparisons because 'inbounds' on
// a GEP only protects against unsigned wrapping.
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_ULT:
case CmpInst::ICMP_ULE:
// However, we have to switch them to their signed variants to handle
// negative indices from the base pointer.
Pred = ICmpInst::getSignedPredicate(Pred);
break;
}
Constant *LHSOffset = stripAndComputeConstantOffsets(TD, LHS);
if (!LHSOffset)
return 0;
Constant *RHSOffset = stripAndComputeConstantOffsets(TD, RHS);
if (!RHSOffset)
return 0;
// If LHS and RHS are not related via constant offsets to the same base
// value, there is nothing we can do here.
if (LHS != RHS)
return 0;
return ConstantExpr::getICmp(Pred, LHSOffset, RHSOffset);
}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
@ -2311,7 +2350,12 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
return getFalse(ITy);
}
// Simplify comparisons of GEPs.
// Simplify comparisons of related pointers using a powerful, recursive
// GEP-walk when we have target data available..
if (Q.TD && LHS->getType()->isPointerTy() && RHS->getType()->isPointerTy())
if (Constant *C = computePointerICmp(*Q.TD, Pred, LHS, RHS))
return C;
if (GetElementPtrInst *GLHS = dyn_cast<GetElementPtrInst>(LHS)) {
if (GEPOperator *GRHS = dyn_cast<GEPOperator>(RHS)) {
if (GLHS->getPointerOperand() == GRHS->getPointerOperand() &&

62
test/Transforms/InstSimplify/compare.ll
View File

@ -103,6 +103,68 @@ define i1 @gep8(%gept* %x) {
; CHECK: ret i1 %equal
}
define i1 @gep9(i8* %ptr) {
; CHECK: @gep9
; CHECK-NOT: ret
; CHECK: ret i1 true
entry:
%first1 = getelementptr inbounds i8* %ptr, i32 0
%first2 = getelementptr inbounds i8* %first1, i32 1
%first3 = getelementptr inbounds i8* %first2, i32 2
%first4 = getelementptr inbounds i8* %first3, i32 4
%last1 = getelementptr inbounds i8* %first2, i32 48
%last2 = getelementptr inbounds i8* %last1, i32 8
%last3 = getelementptr inbounds i8* %last2, i32 -4
%last4 = getelementptr inbounds i8* %last3, i32 -4
%first.int = ptrtoint i8* %first4 to i32
%last.int = ptrtoint i8* %last4 to i32
%cmp = icmp ne i32 %last.int, %first.int
ret i1 %cmp
}
define i1 @gep10(i8* %ptr) {
; CHECK: @gep10
; CHECK-NOT: ret
; CHECK: ret i1 true
entry:
%first1 = getelementptr inbounds i8* %ptr, i32 -2
%first2 = getelementptr inbounds i8* %first1, i32 44
%last1 = getelementptr inbounds i8* %ptr, i32 48
%last2 = getelementptr inbounds i8* %last1, i32 -6
%first.int = ptrtoint i8* %first2 to i32
%last.int = ptrtoint i8* %last2 to i32
%cmp = icmp eq i32 %last.int, %first.int
ret i1 %cmp
}
define i1 @gep11(i8* %ptr) {
; CHECK: @gep11
; CHECK-NOT: ret
; CHECK: ret i1 true
entry:
%first1 = getelementptr inbounds i8* %ptr, i32 -2
%last1 = getelementptr inbounds i8* %ptr, i32 48
%last2 = getelementptr inbounds i8* %last1, i32 -6
%cmp = icmp ult i8* %first1, %last2
ret i1 %cmp
}
define i1 @gep12(i8* %ptr) {
; CHECK: @gep12
; CHECK-NOT: ret
; CHECK: ret i1 %cmp
entry:
%first1 = getelementptr inbounds i8* %ptr, i32 -2
%last1 = getelementptr inbounds i8* %ptr, i32 48
%last2 = getelementptr inbounds i8* %last1, i32 -6
%cmp = icmp slt i8* %first1, %last2
ret i1 %cmp
}
define i1 @zext(i32 %x) {
; CHECK: @zext
%e1 = zext i32 %x to i64