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Fix a bug in Dead Argument Elimination.
If a function seen at compile time is not necessarily the one linked to the binary being built, it is illegal to change the actual arguments passing to it. e.g. -------------------------- void foo(int lol) { // foo() has linkage satisifying isWeakForLinker() // "lol" is not used at all. } void bar(int lo2) { // xform to foo(undef) is illegal, as compiler dose not know which // instance of foo() will be linked to the the binary being built. foo(lol2); } ----------------------------- Such functions can be captured by isWeakForLinker(). NOTE that mayBeOverridden() is insufficient for this purpose as it dosen't include linkage types like AvailableExternallyLinkage and LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of *EQUIVALENT* globals that can be merged at link-time. However, the semantic of *EQUIVALENT*-functions includes parameters. Changing parameters breaks the assumption. Thank John McCall for help, especially for the explanation of subtle difference between linkage types. rdar://11546243 llvm-svn: 192302
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@ -357,6 +357,19 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
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if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
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return false;
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// If a function seen at compile time is not necessarily the one linked to
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// the binary being built, it is illegal to change the actual arguments
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// passing to it. These functions can be captured by isWeakForLinker().
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// *NOTE* that mayBeOverridden() is insufficient for this purpose as it
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// dosen't include linkage types like AvailableExternallyLinkage and
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// LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
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// *EQUIVALENT* globals that can be merged at link-time. However, the
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// semantic of *EQUIVALENT*-functions includes parameters. Changing
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// parameters breaks the assumption.
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//
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if (Fn.isWeakForLinker())
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return false;
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if (Fn.use_empty())
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return false;
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21
test/Transforms/DeadArgElim/linkage.ll
Normal file
21
test/Transforms/DeadArgElim/linkage.ll
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@ -0,0 +1,21 @@
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; RUN: opt < %s -deadargelim -S | FileCheck %s
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; rdar://11546243
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%struct.A = type { i8 }
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define available_externally void @_Z17externallyDefinedP1A(%struct.A* %a) {
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entry:
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call void @_Z3foov()
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ret void
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}
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declare void @_Z3foov()
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define void @_Z4testP1A(%struct.A* %a) {
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; CHECK: @_Z4testP1A
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; CHECK: @_Z17externallyDefinedP1A(%struct.A* %a)
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entry:
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call void @_Z17externallyDefinedP1A(%struct.A* %a)
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ret void
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}
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