Redo "Make global aliases have symbol size equal to their type"

r242520 was reverted in r244313 as the expected behaviour of the alias
attribute in C is that the alias has the same size as the aliasee. However
we can re-introduce adding the size on the alias when the aliasee does not,
from a source code or object perspective, exist as a discrete entity. This
happens when the aliasee is not a symbol, or when that symbol is private.

Differential Revision: http://reviews.llvm.org/D11943

llvm-svn: 244752

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 0ea2c66757a..e69febc6ad6 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1184,6 +1184,20 @@ bool AsmPrinter::doFinalization(Module &M) {
 
     // Emit the directives as assignments aka .set:
     OutStreamer->EmitAssignment(Name, lowerConstant(Alias.getAliasee()));
+
+    // If the aliasee does not correspond to a symbol in the output, i.e. the
+    // alias is not of an object or the aliased object is private, then set the
+    // size of the alias symbol from the type of the alias. We don't do this in
+    // other situations as the alias and aliasee having differing types but same
+    // size may be intentional.
+    const GlobalObject *BaseObject = Alias.getBaseObject();
+    if (MAI->hasDotTypeDotSizeDirective() && Alias.getValueType()->isSized() &&
+        (!BaseObject || BaseObject->hasPrivateLinkage())) {
+      const DataLayout &DL = M.getDataLayout();
+      uint64_t Size = DL.getTypeAllocSize(Alias.getValueType());
+      OutStreamer->emitELFSize(cast<MCSymbolELF>(Name),
+                               MCConstantExpr::create(Size, OutContext));
+    }
   }
 
   GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();