[PATCH] GlobalOpt: Aliases don't have sections, don't copy them when replacing

[Reid Kleckner]

Hi rafael.espindola,

As defined in LangRef, aliases do not have sections.  However, LLVM's
GlobalAlias class inherits from GlobalValue, which means we can read and
set its section.  We should probably ban that as a separate change,
since it doesn't make much sense for an alias to have a section that
differs from its aliasee.

Fixes PR18757, where the section was being lost on the global in code
from Clang like:

extern "C" {
__attribute__((used, section("CUSTOM"))) static int in_custom_section;
}

http://llvm-reviews.chandlerc.com/D2758

Files:
  lib/Transforms/IPO/GlobalOpt.cpp
  test/Transforms/GlobalOpt/alias-resolve.ll
  test/Transforms/GlobalOpt/alias-used-section.ll

Index: lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- lib/Transforms/IPO/GlobalOpt.cpp
+++ lib/Transforms/IPO/GlobalOpt.cpp
@@ -3018,7 +3018,8 @@
       // Give the aliasee the name, linkage and other attributes of the alias.
       Target->takeName(J);
       Target->setLinkage(J->getLinkage());
-      Target->GlobalValue::copyAttributesFrom(J);
+      Target->setVisibility(J->getVisibility());
+      Target->setDLLStorageClass(J->getDLLStorageClass());
 
       if (Used.usedErase(J))
         Used.usedInsert(Target);
Index: test/Transforms/GlobalOpt/alias-resolve.ll
===================================================================
--- test/Transforms/GlobalOpt/alias-resolve.ll
+++ test/Transforms/GlobalOpt/alias-resolve.ll
@@ -1,7 +1,4 @@
-; We use a temporary file so that the test fails when opt crashes.
-
-; RUN: opt < %s -globalopt -S > %t
-; RUN: FileCheck %s < %t
+; RUN: opt < %s -globalopt -S | FileCheck %s
 
 @foo1 = alias void ()* @foo2
 ; CHECK: @foo1 = alias void ()* @foo2
Index: test/Transforms/GlobalOpt/alias-used-section.ll
===================================================================
--- /dev/null
+++ test/Transforms/GlobalOpt/alias-used-section.ll
@@ -0,0 +1,8 @@
+; RUN: opt -S -globalopt < %s | FileCheck %s
+
+ at _Z17in_custom_section = internal global i8 42, section "CUSTOM"
+ at in_custom_section = protected dllexport alias internal i8* @_Z17in_custom_section
+
+; CHECK: @in_custom_section = internal protected dllexport global i8 42, section "CUSTOM"
+
+ at llvm.used = appending global [1 x i8*] [i8* @in_custom_section], section "llvm.metadata"
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