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Change hasUniqueInitializer() to call isStrongDefinitionForLinker() instead of !isWeakForLinker()

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Summary:
Available_externally global variable with initializer were considered "hasInitializer()",
while obviously it can't match the description:

    Whether the global variable has an initializer, and any changes made to the
    initializer will turn up in the final executable.

since modifying the initializer of an externally available variable does not make sense.

Reviewers: pcc, rafael

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15351

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 255123
This commit is contained in:
Mehdi Amini 2015-12-09 16:17:07 +00:00
parent d19d7b747a
commit 300ed48d90
2 changed files with 29 additions and 12 deletions
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19
include/llvm/IR/GlobalVariable.h
View File

@ -105,18 +105,13 @@ public:
/// hasUniqueInitializer - Whether the global variable has an initializer, and
/// any changes made to the initializer will turn up in the final executable.
inline bool hasUniqueInitializer() const {
return hasInitializer() &&
// It's not safe to modify initializers of global variables with weak
// linkage, because the linker might choose to discard the initializer and
// use the initializer from another instance of the global variable
// instead. It is wrong to modify the initializer of a global variable
// with *_odr linkage because then different instances of the global may
// have different initializers, breaking the One Definition Rule.
!isWeakForLinker() &&
// It is not safe to modify initializers of global variables with the
// external_initializer marker since the value may be changed at runtime
// before C++ initializers are evaluated.
!isExternallyInitialized();
return
// We need to be sure this is the definition that will actually be used
isStrongDefinitionForLinker() &&
// It is not safe to modify initializers of global variables with the
// external_initializer marker since the value may be changed at runtime
// before C++ initializers are evaluated.
!isExternallyInitialized();
}
/// getInitializer - Return the initializer for this global variable. It is

22
test/Transforms/GlobalOpt/available_externally_global_ctors.ll Normal file
View File

@ -0,0 +1,22 @@
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.11.0"
; RUN: opt -S -globalopt < %s | FileCheck %s
; Verify that the initialization of the available_externally global is not eliminated
; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @foo_static_init, i8* null }]
@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @foo_static_init, i8* null }]
@foo_external = available_externally global void ()* null
define internal void @foo_static_init() {
entry:
store void ()* @foo_impl, void ()** @foo_external
ret void
}
define internal void @foo_impl() {
entry:
ret void
}