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Don't infer whether a value is captured in the current function from the

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'nocapture' attribute.

The nocapture attribute only specifies that no copies are made that
outlive the function. This isn't the same as there being no copies at all.
This fixes PR14045.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167381 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Osborne 2012-11-05 10:48:24 +00:00
parent e507fc6eea
commit 544533301e
2 changed files with 26 additions and 5 deletions
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10
lib/Analysis/BasicAliasAnalysis.cpp
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@ -58,12 +58,12 @@ static bool isNonEscapingLocalObject(const Value *V) {
// then it has not escaped before entering the function. Check if it escapes
// inside the function.
if (const Argument *A = dyn_cast<Argument>(V))
if (A->hasByValAttr() || A->hasNoAliasAttr()) {
// Don't bother analyzing arguments already known not to escape.
if (A->hasNoCaptureAttr())
return true;
if (A->hasByValAttr() || A->hasNoAliasAttr())
// Note even if the argument is marked nocapture we still need to check
// for copies made inside the function. The nocapture attribute only
// specifies that there are no copies made that outlive the function.
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
}
return false;
}

21
test/Analysis/BasicAA/nocapture.ll
View File

@ -13,3 +13,24 @@ define i32 @test2() {
ret i32 %c
}
declare void @test3(i32** %p, i32* %q) nounwind
define i32 @test4(i32* noalias nocapture %p) nounwind {
; CHECK: call void @test3
; CHECK: store i32 0, i32* %p
; CHECK: store i32 1, i32* %x
; CHECK: %y = load i32* %p
; CHECK: ret i32 %y
entry:
%q = alloca i32*
; Here test3 might store %p to %q. This doesn't violate %p's nocapture
; attribute since the copy doesn't outlive the function.
call void @test3(i32** %q, i32* %p) nounwind
store i32 0, i32* %p
%x = load i32** %q
; This store might write to %p and so we can't eliminate the subsequent
; load
store i32 1, i32* %x
%y = load i32* %p
ret i32 %y
}