fix PR6921 a different way. Intead of increasing the

alignment of globals with a specified alignment, we fix
common variables to obey their alignment.  Add a comment
explaining why this behavior is important.

llvm-svn: 102365

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 4660e1b2ccd..6fc883359be 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -228,7 +228,15 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
 
   const TargetData *TD = TM.getTargetData();
   unsigned Size = TD->getTypeAllocSize(GV->getType()->getElementType());
-  unsigned AlignLog = TD->getPreferredAlignmentLog(GV);
+  
+  // If the alignment is specified, we *must* obey it.  Overaligning a global
+  // with a specified alignment is a prompt way to break globals emitted to
+  // sections and expected to be contiguous (e.g. ObjC metadata).
+  unsigned AlignLog;
+  if (unsigned GVAlign = GV->getAlignment())
+    AlignLog = Log2_32(GVAlign);
+  else
+    AlignLog = TD->getPreferredAlignmentLog(GV);
   
   // Handle common and BSS local symbols (.lcomm).
   if (GVKind.isCommon() || GVKind.isBSSLocal()) {