Add Available Externally linkage type to isWeakForLinker()

[mehdi_amini]

Summary

Per LangRef: "Globals with available_externally linkage are
allowed to be discarded at will, and are otherwise the same
as linkonce_odr", since linkonce_odr is in this list it makes
sense to have available_externally there as well.

[• rafael]

LGTM

test/Transforms/GlobalOpt/available_externally_global_ctors.ll

18

Please clean up the test.

You don't need the comments, the #0, the alignment, etc.

[mehdi_amini]

r255043

[pcc]

I don't think this is right. It basically reverts part of D10941.

Should we instead fix globaldce to do the right thing with these types of globals?

[mehdi_amini]

We can fix whatever transformation is wrong because of that, but we first have to fix the LangRef...

[pcc]

D15343 is the wording change for the LangRef.

[• rafael]

Yes, sorry. I think my review was wrong.

It would be reasonable for isWeakForLinker to return true iff it
returned true for declarations, which is not the case.

Sorry,
Rafael

include/llvm/IR/GlobalValue.h

public:
 
   /// Whether the definition of this global may be replaced at link time.  NB:
   /// Using this method outside of the code generators is almost always a
   /// mistake: when working at the IR level use mayBeOverridden instead as it
   /// knows about ODR semantics.
   static bool isWeakForLinker(LinkageTypes Linkage)  {
     return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
            Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
-           Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
+           Linkage == CommonLinkage || Linkage == ExternalWeakLinkage ||
+           Linkage == AvailableExternallyLinkage;
   }
 
   bool hasExternalLinkage() const { return isExternalLinkage(Linkage); }
   bool hasAvailableExternallyLinkage() const {
     return isAvailableExternallyLinkage(Linkage);
   }
   bool hasLinkOnceLinkage() const {
     return isLinkOnceLinkage(Linkage);

test/Transforms/GlobalOpt/available_externally_global_ctors.ll

+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 }]
+
[e-mail]_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, align 8
+
+define internal void @foo_static_init() {
+entry:
+  store void ()* @foo_impl, void ()** @foo_external, align 8
+  ret void
+}
+
+; Function Attrs: norecurse nounwind readnone ssp uwtable
+define internal void @foo_impl() #0 {
+entry:
+  ret void
+}
+