Merging r304537:

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r304537 | john.brawn | 2017-06-02 06:24:14 -0400 (Fri, 02 Jun 2017) | 9 lines

[GlobalMerge] Don't merge globals that may be preempted

When a global may be preempted it needs to be accessed directly, instead of
indirectly through a MergedGlobals symbol, for the preemption to work.

This fixes PR33136.

Differential Revision: https://reviews.llvm.org/D33727

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_40@305187 91177308-0d34-0410-b5e6-96231b3b80d8

Author: tstellar

lib/CodeGen/GlobalMerge.cpp

@@ -559,6 +559,10 @@ bool GlobalMerge::doInitialization(Module &M) {
     if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasSection())
       continue;
 
+    // It's not safe to merge globals that may be preempted
+    if (TM && !TM->shouldAssumeDSOLocal(M, &GV))
+      continue;
+
     if (!(MergeExternalGlobals && GV.hasExternalLinkage()) &&
         !GV.hasInternalLinkage())
       continue;

test/CodeGen/ARM/global-merge-external.ll

@@ -2,6 +2,7 @@
 ; RUN: llc < %s -mtriple=arm-eabi  -arm-global-merge -global-merge-on-external=true  | FileCheck %s --check-prefix=CHECK-MERGE
 ; RUN: llc < %s -mtriple=arm-eabi  -arm-global-merge -global-merge-on-external=false | FileCheck %s --check-prefix=CHECK-NO-MERGE
 ; RUN: llc < %s -mtriple=arm-macho -arm-global-merge                                 | FileCheck %s --check-prefix=CHECK-NO-MERGE
+; RUN: llc < %s -mtriple=arm-eabi  -arm-global-merge -relocation-model=pic           | FileCheck %s --check-prefix=CHECK-NO-MERGE
 
 @x = global i32 0, align 4
 @y = global i32 0, align 4