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[TSan, SanitizerBinaryMetadata] Improve instrument for derived pointers via phis/selects #132752

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Merged
merged 1 commit into from
Apr 17, 2025
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[TSan, SanitizerBinaryMetadata] Improve instrument for derived pointers via phis/selects #132752

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4 changes: 2 additions & 2 deletions llvm/lib/Transforms/Instrumentation/SanitizerBinaryMetadata.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -393,8 +393,8 @@ bool maybeSharedMutable(const Value *Addr) {
if (!Addr)
return true;

if (isa<AllocaInst>(getUnderlyingObject(Addr)) &&
!PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true))
const AllocaInst *AI = findAllocaForValue(Addr);
if (AI && !PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true))
return false; // Object is on stack but does not escape.

Addr = Addr->stripInBoundsOffsets();
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4 changes: 2 additions & 2 deletions llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
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Expand Up @@ -448,8 +448,8 @@ void ThreadSanitizer::chooseInstructionsToInstrument(
}
}

if (isa<AllocaInst>(getUnderlyingObject(Addr)) &&
!PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true)) {
const AllocaInst *AI = findAllocaForValue(Addr);
if (AI && !PointerMayBeCaptured(Addr, /*ReturnCaptures=*/true)) {
// The variable is addressable but not captured, so it cannot be
// referenced from a different thread and participate in a data race
// (see llvm/Analysis/CaptureTracking.h for details).
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31 changes: 31 additions & 0 deletions llvm/test/Instrumentation/ThreadSanitizer/capture.ll
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Expand Up @@ -88,4 +88,35 @@ entry:
; CHECK: __tsan_write
; CHECK: ret void

define void @notcaptured3(i1 %cond) nounwind uwtable sanitize_thread {
entry:
%stkobj = alloca [2 x i32], align 8
%derived = getelementptr inbounds i32, ptr %stkobj, i64 1
%ptr = select i1 %cond, ptr %derived, ptr %stkobj
store i32 42, ptr %ptr, align 4
ret void
}
; CHECK-LABEL: define void @notcaptured3
; CHECK-NOT: call void @__tsan_write4(ptr %ptr)
; CHECK: ret void

define void @notcaptured4() nounwind uwtable sanitize_thread {
entry:
%stkobj = alloca [10 x i8], align 1
br label %loop

exit:
ret void

loop:
%count = phi i32 [ 0, %entry ], [ %addone, %loop ]
%derived = phi ptr [ %stkobj, %entry ], [ %ptraddone, %loop ]
store i32 %count, ptr %derived, align 4
%ptraddone = getelementptr inbounds i32, ptr %derived, i64 1
%addone = add nuw nsw i32 %count, 1
%eq10 = icmp eq i32 %addone, 10
br i1 %eq10, label %exit, label %loop
}
; CHECK-LABEL: define void @notcaptured4
; CHECK: ret void
; CHECK-NOT: call void @__tsan_write4(ptr %derived)