[PATCH] CodeGen: Emit globals with a constant initializer but no definition as available_externally.

[Reid Kleckner]

================
Comment at: lib/CodeGen/CodeGenModule.cpp:1244-1247
@@ +1243,6 @@
+bool CodeGenModule::shouldEmitGlobalVariable(const VarDecl *VD) {
+  if (GetLLVMLinkageVarDefinition(VD, /*isConstant=*/true) !=
+      llvm::Function::AvailableExternallyLinkage)
+    return true;
+  return CodeGenOpts.OptimizationLevel != 0;
+}
----------------
This seems more intuitive as:

  if (isAvailableExternally)
    return CGO.OptLevel != 0;
  return true;

Also, how do we know isConstant is true?  Can you assert that it is like you do below?

================
Comment at: lib/CodeGen/CodeGenModule.cpp:1846
@@ +1845,3 @@
+           "Variable with init but no definition should be constant!");
+    return llvm::GlobalValue::AvailableExternallyLinkage;
+  }
----------------
What if the variable is thread local, or fits any of the below special cases involving templates?  This probably goes towards the end of the if/else chain, not first, considering that it's for an optimization.


http://llvm-reviews.chandlerc.com/D1982