From e549e39190589b6ce6f9f865bc030eb0b95bf724 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Tue, 9 Sep 2014 15:59:12 +0000
Subject: [PATCH] When merging two common GlobalValues, keep the largest.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217451 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Linker/LinkModules.cpp     | 19 +++++++++++++++++--
 test/Linker/Inputs/linkage2.ll |  2 ++
 test/Linker/linkage2.ll        |  7 +++++--
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/lib/Linker/LinkModules.cpp b/lib/Linker/LinkModules.cpp
index 87d075fb03e..65fe30c94f7 100644
--- a/lib/Linker/LinkModules.cpp
+++ b/lib/Linker/LinkModules.cpp
@@ -688,6 +688,9 @@ bool ModuleLinker::shouldLinkFromSource(const GlobalValue &Dest,
   bool SrcIsDeclaration = isDeclaration(Src);
   bool DestIsDeclaration = isDeclaration(Dest);
 
+  // FIXME: Make datalayout mandatory and just use getDataLayout().
+  DataLayout DL(Dest.getParent());
+
   if (SrcIsDeclaration) {
     // If Src is external or if both Src & Dest are external..  Just link the
     // external globals, we aren't adding anything.
@@ -702,14 +705,26 @@ bool ModuleLinker::shouldLinkFromSource(const GlobalValue &Dest,
     // If Dest is external but Src is not:
     return true;
 
+  if (Src.hasCommonLinkage()) {
+    if (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage())
+      return true;
+
+    if (!Dest.hasCommonLinkage())
+      return false;
+
+    uint64_t DestSize = DL.getTypeAllocSize(Dest.getType()->getElementType());
+    uint64_t SrcSize = DL.getTypeAllocSize(Src.getType()->getElementType());
+    return SrcSize > DestSize;
+  }
+
   if (Src.isWeakForLinker()) {
     assert(!Dest.hasExternalWeakLinkage());
     assert(!Dest.hasAvailableExternallyLinkage());
+
     if (Dest.hasLinkOnceLinkage() && Src.hasWeakLinkage())
       return true;
 
-    return (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage()) &&
-           Src.hasCommonLinkage();
+    return false;
   }
 
   if (Dest.isWeakForLinker()) {
diff --git a/test/Linker/Inputs/linkage2.ll b/test/Linker/Inputs/linkage2.ll
index 6ecaeb55a0f..6f320e40e0a 100644
--- a/test/Linker/Inputs/linkage2.ll
+++ b/test/Linker/Inputs/linkage2.ll
@@ -1,3 +1,5 @@
 @test1_a = weak global i8 1
 
 @test2_a = external dllimport global i8
+
+@test3_a = common global i16 0
diff --git a/test/Linker/linkage2.ll b/test/Linker/linkage2.ll
index 99cb22c05c2..283a3b941df 100644
--- a/test/Linker/linkage2.ll
+++ b/test/Linker/linkage2.ll
@@ -2,7 +2,10 @@
 ; RUN: llvm-link %p/Inputs/linkage2.ll %s -S | FileCheck %s
 
 @test1_a = common global i8 0
-; CHECK: @test1_a = common global i8 0
+; CHECK-DAG: @test1_a = common global i8 0
 
 @test2_a = global i8 0
-; CHECK: @test2_a = global i8 0
+; CHECK-DAG: @test2_a = global i8 0
+
+@test3_a = common global i8 0
+; CHECK-DAG: @test3_a = common global i16 0
-- 
2.34.1