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fix PR6921 a different way. Intead of increasing the

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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
This commit is contained in:
Chris Lattner 2010-04-26 18:46:46 +00:00
parent 6fa7636e61
commit 567dd1f5d0
3 changed files with 28 additions and 1 deletions
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10
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
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@ -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()) {

18
test/CodeGen/X86/alignment.ll Normal file
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@ -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

1
test/CodeGen/X86/unaligned-load.ll
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@ -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"