From 567dd1f5d0ae454e7c51ef070bbb8d31a43ed4bc Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 26 Apr 2010 18:46:46 +0000
Subject: [PATCH] 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102365 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/AsmPrinter/AsmPrinter.cpp | 10 +++++++++-
 test/CodeGen/X86/alignment.ll         | 18 ++++++++++++++++++
 test/CodeGen/X86/unaligned-load.ll    |  1 +
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/CodeGen/X86/alignment.ll

diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 4660e1b2ccd..6fc883359be 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/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()) {
diff --git a/test/CodeGen/X86/alignment.ll b/test/CodeGen/X86/alignment.ll
new file mode 100644
index 00000000000..06a4f3f8e88
--- /dev/null
+++ b/test/CodeGen/X86/alignment.ll
@@ -0,0 +1,18 @@
+; RUN: llc %s -o - -mtriple=x86_64-linux-gnu | FileCheck %s
+
+; This cannot get rounded up to the preferred alignment (16) if they have an
+; explicit alignment specified.
+@GlobalA = global { [384 x i8] } zeroinitializer, align 8 
+
+; CHECK:	.bss
+; CHECK:	.globl	GlobalA
+; CHECK:	.align	8
+; CHECK: GlobalA:
+; CHECK:	.zero	384
+
+; Common variables should not get rounded up to the preferred alignment (16) if
+; they have an explicit alignment specified.
+; PR6921
+@GlobalB = common global { [384 x i8] } zeroinitializer, align 8
+
+; CHECK: 	.comm	GlobalB,384,8
\ No newline at end of file
diff --git a/test/CodeGen/X86/unaligned-load.ll b/test/CodeGen/X86/unaligned-load.ll
index e210531068e..b26097f31b4 100644
--- a/test/CodeGen/X86/unaligned-load.ll
+++ b/test/CodeGen/X86/unaligned-load.ll
@@ -28,6 +28,7 @@ return:
 
 declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
 
+; CORE2: .section
 ; CORE2: .align  3
 ; CORE2-NEXT: _.str1:
 ; CORE2-NEXT: .asciz "DHRYSTONE PROGRAM, SOME STRING"