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Prevent alias from pointing to weak aliases.

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Committed
rafaelMar 27 2014, 8:26 AM
Parents
rL204933: [OPENMP] OMPExecutableDirective re-factoring
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Description

Prevent alias from pointing to weak aliases.

This adds back r204781.

Original message:

Aliases are just another name for a position in a file. As such, the
regular symbol resolutions are not applied. For example, given

define void @my_func() {

ret void

}
@my_alias = alias weak void ()* @my_func
@my_alias2 = alias void ()* @my_alias

We produce without this patch:

.weak   my_alias

my_alias = my_func

.globl  my_alias2

my_alias2 = my_alias

That is, in the resulting ELF file my_alias, my_func and my_alias are
just 3 names pointing to offset 0 of .text. That is *not* the
semantics of IR linking. For example, linking in a

@my_alias = alias void ()* @other_func

would require the strong my_alias to override the weak one and
my_alias2 would end up pointing to other_func.

There is no way to represent that with aliases being just another
name, so the best solution seems to be to just disallow it, converting
a miscompile into an error.

rL204934

llvm/trunk/docs/LangRef.rst

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llvm/trunk/include/llvm/IR/GlobalAlias.h

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llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

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llvm/trunk/lib/ExecutionEngine/JIT/JITEmitter.cpp

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llvm/trunk/lib/IR/Globals.cpp

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llvm/trunk/lib/IR/Verifier.cpp

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llvm/trunk/lib/Target/PowerPC/PPCAsmPrinter.cpp

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llvm/trunk/lib/Target/PowerPC/PPCFastISel.cpp

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llvm/trunk/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

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llvm/trunk/lib/Target/TargetMachine.cpp

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llvm/trunk/lib/Target/X86/X86FastISel.cpp

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llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

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llvm/trunk/lib/Target/XCore/XCoreISelLowering.cpp

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llvm/trunk/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

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llvm/trunk/test/CodeGen/X86/dllexport-x86_64.ll

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llvm/trunk/test/CodeGen/X86/dllexport.ll

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llvm/trunk/test/Feature/aliases.ll

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llvm/trunk/test/Transforms/GlobalOpt/alias-resolve.ll

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