Skip to content

[BasicAA] Gracefully handle large LocationSize #138528

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
May 6, 2025
Merged

[BasicAA] Gracefully handle large LocationSize #138528

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
36c3fcf
[BasicAA] Gracefully handle large LocationSize
nikic May 5, 2025
caebfd4
fix test
nikic May 5, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 5 additions & 3 deletions llvm/lib/Analysis/BasicAliasAnalysis.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1237,8 +1237,11 @@ AliasResult BasicAAResult::aliasGEP(
if (V1Size.isScalable() || V2Size.isScalable())
return AliasResult::MayAlias;

// We need to know both acess sizes for all the following heuristics.
if (!V1Size.hasValue() || !V2Size.hasValue())
// We need to know both access sizes for all the following heuristics. Don't
// try to reason about sizes larger than the index space.
unsigned BW = DecompGEP1.Offset.getBitWidth();
if (!V1Size.hasValue() || !V2Size.hasValue() ||
!isUIntN(BW, V1Size.getValue()) || !isUIntN(BW, V2Size.getValue()))
return AliasResult::MayAlias;

APInt GCD;
Expand Down Expand Up @@ -1293,7 +1296,6 @@ AliasResult BasicAAResult::aliasGEP(

// Compute ranges of potentially accessed bytes for both accesses. If the
// interseciton is empty, there can be no overlap.
unsigned BW = OffsetRange.getBitWidth();
ConstantRange Range1 = OffsetRange.add(
ConstantRange(APInt(BW, 0), APInt(BW, V1Size.getValue())));
ConstantRange Range2 =
Expand Down
14 changes: 14 additions & 0 deletions llvm/test/Analysis/BasicAA/size-overflow.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
; RUN: opt -passes=aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s

target datalayout = "p:32:32"

; Make sure that using a LocationSize larget than the index space does not
; assert.

; Just Mod: Ptr: i32* %gep <-> call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 68719476736, i1 false)
Copy link
Contributor

@fhahn fhahn May 5, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Missing CHECK below?

Suggested change
; Just Mod: Ptr: i32* %gep <-> call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 68719476736, i1 false)
; CHECK: Just Mod: Ptr: i32* %gep <-> call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 68719476736, i1 false)

Copy link
Contributor Author

@nikic nikic May 5, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Oops, looks like I never actually ran the new test...

define void @test(ptr %p, i32 %idx) {
%gep = getelementptr i8, ptr %p, i32 %idx
load i32, ptr %gep
call void @llvm.memset.i64(ptr %p, i8 0, i64 u0x100000000, i1 false)
ret void
}
Loading