From: John Brawn <john.brawn@arm.com>
Date: Wed, 12 Aug 2015 13:36:48 +0000 (+0000)
Subject: [GlobalMerge] Only emit aliases for internal linkage variables for non-Mach-O
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1a5ed7be24acd9035006af4de59bb78d190bd0cc;p=oota-llvm.git

[GlobalMerge] Only emit aliases for internal linkage variables for non-Mach-O

On Mach-O emitting aliases for the variables that make up a MergedGlobals
variable can cause problems when linking with dead stripping enabled so don't
do that, except for external variables where we must emit an alias.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244748 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/GlobalMerge.cpp b/lib/CodeGen/GlobalMerge.cpp
index 3a7e2f47686..d8739c4aaac 100644
--- a/lib/CodeGen/GlobalMerge.cpp
+++ b/lib/CodeGen/GlobalMerge.cpp
@@ -459,9 +459,16 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable *> &Globals,
       Globals[k]->replaceAllUsesWith(GEP);
       Globals[k]->eraseFromParent();
 
-      // Generate a new alias...
-      auto *PTy = cast<PointerType>(GEP->getType());
-      GlobalAlias::create(PTy, Linkage, Name, GEP, &M);
+      // When the linkage is not internal we must emit an alias for the original
+      // variable name as it may be accessed from another object. On non-Mach-O
+      // we can also emit an alias for internal linkage as it's safe to do so.
+      // It's not safe on Mach-O as the alias (and thus the portion of the
+      // MergedGlobals variable) may be dead stripped at link time.
+      if (Linkage != GlobalValue::InternalLinkage ||
+          !TM->getTargetTriple().isOSBinFormatMachO()) {
+        auto *PTy = cast<PointerType>(GEP->getType());
+        GlobalAlias::create(PTy, Linkage, Name, GEP, &M);
+      }
 
       NumMerged++;
     }
diff --git a/test/CodeGen/AArch64/global-merge-1.ll b/test/CodeGen/AArch64/global-merge-1.ll
index 304d0a78c2c..b93f41c07df 100644
--- a/test/CodeGen/AArch64/global-merge-1.ll
+++ b/test/CodeGen/AArch64/global-merge-1.ll
@@ -23,5 +23,9 @@ define void @f1(i32 %a1, i32 %a2) {
 ;CHECK:	.type	.L_MergedGlobals,@object  // @_MergedGlobals
 ;CHECK:	.local	.L_MergedGlobals
 ;CHECK:	.comm	.L_MergedGlobals,8,8
+;CHECK: m = .L_MergedGlobals
+;CHECK: n = .L_MergedGlobals+4
 
 ;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals,8,3 ; @_MergedGlobals
+;CHECK-APPLE-IOS-NOT: _m = l__MergedGlobals
+;CHECK-APPLE-IOS-NOT: _n = l__MergedGlobals+4
diff --git a/test/CodeGen/AArch64/global-merge-3.ll b/test/CodeGen/AArch64/global-merge-3.ll
index a6a8a7e8a04..095fa4f7881 100644
--- a/test/CodeGen/AArch64/global-merge-3.ll
+++ b/test/CodeGen/AArch64/global-merge-3.ll
@@ -36,11 +36,13 @@ define void @f1(i32 %a1, i32 %a2, i32 %a3) {
 
 ;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals.1,4000,4
 
+;CHECK: z = .L_MergedGlobals
 ;CHECK:	.globl	x
 ;CHECK: x = .L_MergedGlobals+4
 ;CHECK:	.globl	y
 ;CHECK: y = .L_MergedGlobals.1
 
+;CHECK-APPLE-IOS-NOT: _z = l__MergedGlobals
 ;CHECK-APPLE-IOS:.globl	_x
 ;CHECK-APPLE-IOS: _x = l__MergedGlobals+4
 ;CHECK-APPLE-IOS:.globl	_y