c6692f819e
Generalize D99629 for ELF. A default visibility non-local symbol is preemptible
in a -shared link. `isInterposable` is an insufficient condition.
Moreover, a non-preemptible alias may be referenced in a sub constant expression
which intends to lower to a PC-relative relocation. Replacing the alias with a
preemptible aliasee may introduce a linker error.
Respect dso_preemptable and suppress optimization to fix the abose issues. With
the change, `alias = 345` will not be rewritten to use aliasee in a `-fpic`
compile.
```
int aliasee;
extern int alias __attribute__((alias("aliasee"), visibility("hidden")));
void foo() { alias = 345; } // intended to access the local copy
```
While here, refine the condition for the alias as well.
For some binary formats like COFF, `isInterposable` is a sufficient condition.
But I think canonicalization for the changed case has little advantage, so I
don't bother to add the `Triple(M.getTargetTriple()).isOSBinFormatELF()` or
`getPICLevel/getPIELevel` complexity.
For instrumentations, it's recommended not to create aliases that refer to
globals that have a weak linkage or is preemptible. However, the following is
supported and the IR needs to handle such cases.
```
int aliasee __attribute__((weak));
extern int alias __attribute__((alias("aliasee")));
```
There are other places where GlobalAlias isInterposable usage may need to be
fixed.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D107249
67 lines
1.8 KiB
LLVM
67 lines
1.8 KiB
LLVM
; RUN: opt < %s -passes=globalopt -S | FileCheck %s
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@foo1 = alias void (), void ()* @foo2
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;; foo2 is dso_local and non-weak. Resolved.
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; CHECK: @foo1 = alias void (), void ()* @bar2
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@foo2 = dso_local alias void(), void()* @bar1
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;; bar1 is dso_local and non-weak. Resolved.
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; CHECK: @foo2 = dso_local alias void (), void ()* @bar2
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@bar1 = dso_local alias void (), void ()* @bar2
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; CHECK: @bar1 = dso_local alias void (), void ()* @bar2
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@weak1 = weak dso_local alias void (), void ()* @bar2
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;; weak1 may be replaced with another definition in the linkage unit. Not resolved.
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; CHECK: @weak1 = weak dso_local alias void (), void ()* @bar2
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@bar4 = private unnamed_addr constant [2 x i8*] zeroinitializer
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@foo4 = weak_odr unnamed_addr alias i8*, getelementptr inbounds ([2 x i8*], [2 x i8*]* @bar4, i32 0, i32 1)
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; CHECK: @foo4 = weak_odr unnamed_addr alias i8*, getelementptr inbounds ([2 x i8*], [2 x i8*]* @bar4, i32 0, i32 1)
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@priva = private alias void (), void ()* @bar5
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; CHECK: @priva = private alias void (), void ()* @bar5
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define dso_local void @bar2() {
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ret void
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}
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; CHECK: define dso_local void @bar2()
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define weak void @bar5() {
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ret void
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}
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; CHECK: define weak void @bar5()
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define void @baz() {
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entry:
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call void @foo1()
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;; foo1 is dso_preemptable. Not resolved.
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; CHECK: call void @foo1()
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call void @foo2()
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;; foo2 is dso_local and non-weak. Resolved.
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; CHECK: call void @bar2()
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call void @bar1()
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;; bar1 is dso_local and non-weak. Resolved.
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; CHECK: call void @bar2()
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call void @weak1()
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;; weak1 is weak. Not resolved.
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; CHECK: call void @weak1()
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call void @priva()
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;; priva has a local linkage. Resolved.
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; CHECK: call void @priva()
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ret void
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}
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@foo3 = dso_local alias void (), void ()* @bar3
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; CHECK-NOT: bar3
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define internal void @bar3() {
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ret void
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}
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;CHECK: define dso_local void @foo3
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