IR: Do not consider available_externally linkage to be linker-weak.

From the linker's perspective, an available_externally global is equivalent
to an external declaration (per isDeclarationForLinker()), so it is incorrect
to consider it to be a weak definition.

Also clean up some logic in the dead argument elimination pass and clarify
its comments to better explain how its behavior depends on linkage,
introduce GlobalValue::isStrongDefinitionForLinker() and start using
it throughout the optimizers and backend.

Differential Revision: http://reviews.llvm.org/D10941

llvm-svn: 241413

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index c45005f343d..fa0d7798cae 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1464,7 +1464,7 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
           // If the object is defined in the current Module, we'll be giving
           // it the preferred alignment. Otherwise, we have to assume that it
           // may only have the minimum ABI alignment.
-          if (!GVar->isDeclaration() && !GVar->isWeakForLinker())
+          if (GVar->isStrongDefinitionForLinker())
             Align = DL.getPreferredAlignment(GVar);
           else
             Align = DL.getABITypeAlignment(ObjectType);