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Avoid combining GEPs that might overflow at runtime.

Browse Source 
rdar://problem/9267970

Patch by Julien Lerouge!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131339 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Stuart Hastings 2011-05-14 05:55:10 +00:00
parent d0118a2371
commit 67f071e697
2 changed files with 22 additions and 1 deletions
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4
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -634,6 +634,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
if (AllZeros)
return FoldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I);
bool GEPsInBounds = GEPLHS->isInBounds() && GEPRHS->isInBounds();
if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) {
// If the GEPs only differ by one index, compare it.
unsigned NumDifferences = 0; // Keep track of # differences.
@ -656,7 +657,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
ConstantInt::get(Type::getInt1Ty(I.getContext()),
ICmpInst::isTrueWhenEqual(Cond)));
else if (NumDifferences == 1) {
else if (NumDifferences == 1 && GEPsInBounds) {
Value *LHSV = GEPLHS->getOperand(DiffOperand);
Value *RHSV = GEPRHS->getOperand(DiffOperand);
// Make sure we do a signed comparison here.
@ -667,6 +668,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
// Only lower this if the icmp is the only user of the GEP or if we expect
// the result to fold to a constant!
if (TD &&
GEPsInBounds &&
(isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
(isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2)

19
test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: opt < %s -instcombine | lli
; rdar://problem/9267970
; ideally this test will run on a 32-bit host
; must not discard GEPs that might overflow at runtime (aren't inbounds)
define i32 @main(i32 %argc) {
entry:
%tmp1 = add i32 %argc, -2
%tmp2 = add i32 %argc, 1879048192
%p = alloca i8
%p1 = getelementptr i8* %p, i32 %tmp1
%p2 = getelementptr i8* %p, i32 %tmp2
%cmp = icmp ult i8* %p1, %p2
br i1 %cmp, label %bbtrue, label %bbfalse
bbtrue: ; preds = %entry
ret i32 -1
bbfalse: ; preds = %entry
ret i32 0
}