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, 12 insertions, 24 deletions

diff --git a/llvm/lib/Target/ARM/ARMSubtarget.cpp b/llvm/lib/Target/ARM/ARMSubtarget.cpp
index 55808dfb9ef..af18eeabf0e 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.cpp
+++ b/llvm/lib/Target/ARM/ARMSubtarget.cpp
@@ -286,7 +286,7 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
   if (RelocM == Reloc::Static)
     return false;
 
-  bool isDecl = GV->isDeclarationForLinker();
+  bool isDef = GV->isStrongDefinitionForLinker();
 
   if (!isTargetMachO()) {
     // Extra load is needed for all externally visible.
@@ -294,34 +294,22 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
       return false;
     return true;
   } else {
-    if (RelocM == Reloc::PIC_) {
-      // If this is a strong reference to a definition, it is definitely not
-      // through a stub.
-      if (!isDecl && !GV->isWeakForLinker())
-        return false;
-
-      // Unless we have a symbol with hidden visibility, we have to go through a
-      // normal $non_lazy_ptr stub because this symbol might be resolved late.
-      if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
-        return true;
+    // If this is a strong reference to a definition, it is definitely not
+    // through a stub.
+    if (isDef)
+      return false;
+
+    // Unless we have a symbol with hidden visibility, we have to go through a
+    // normal $non_lazy_ptr stub because this symbol might be resolved late.
+    if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
+      return true;
 
+    if (RelocM == Reloc::PIC_) {
       // If symbol visibility is hidden, we have a stub for common symbol
       // references and external declarations.
-      if (isDecl || GV->hasCommonLinkage())
+      if (GV->isDeclarationForLinker() || GV->hasCommonLinkage())
         // Hidden $non_lazy_ptr reference.
         return true;
-
-      return false;
-    } else {
-      // If this is a strong reference to a definition, it is definitely not
-      // through a stub.
-      if (!isDecl && !GV->isWeakForLinker())
-        return false;
-
-      // Unless we have a symbol with hidden visibility, we have to go through a
-      // normal $non_lazy_ptr stub because this symbol might be resolved late.
-      if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
-        return true;
     }
   }