[llvm] r239560 - Object: Prepend __imp_ when mangling a dllimport symbol in IRObjectFile.

[Peter Collingbourne]

Author: pcc
Date: Thu Jun 11 16:42:18 2015
New Revision: 239560

URL: http://llvm.org/viewvc/llvm-project?rev=239560&view=rev
Log:
Object: Prepend __imp_ when mangling a dllimport symbol in IRObjectFile.

We cannot prepend __imp_ in the IR mangler because a function reference may
be emitted unmangled in a constant initializer. The linker is expected to
resolve such references to thunks. This is covered by the new test case.

Strictly speaking we ought to emit two undefined symbols, one with __imp_ and
one without, as we cannot know which symbol the final object file will refer
to. However, this would require rather intrusive changes to IRObjectFile,
and lld works fine without it for now.

This reimplements r239437, which was reverted in r239502.

Differential Revision: http://reviews.llvm.org/D10400

Added:
    llvm/trunk/test/Object/dllimport.ll
Modified:
    llvm/trunk/lib/Object/IRObjectFile.cpp
    llvm/trunk/test/CodeGen/X86/dllimport.ll

Modified: llvm/trunk/lib/Object/IRObjectFile.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/IRObjectFile.cpp?rev=239560&r1=239559&r2=239560&view=diff
==============================================================================
--- llvm/trunk/lib/Object/IRObjectFile.cpp (original)
+++ llvm/trunk/lib/Object/IRObjectFile.cpp Thu Jun 11 16:42:18 2015
@@ -198,6 +198,9 @@ std::error_code IRObjectFile::printSymbo
     return std::error_code();
   }
 
+  if (GV->hasDLLImportStorageClass())
+    OS << "__imp_";
+
   if (Mang)
     Mang->getNameWithPrefix(OS, GV, false);
   else

Modified: llvm/trunk/test/CodeGen/X86/dllimport.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/dllimport.ll?rev=239560&r1=239559&r2=239560&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/dllimport.ll (original)
+++ llvm/trunk/test/CodeGen/X86/dllimport.ll Thu Jun 11 16:42:18 2015
@@ -57,3 +57,7 @@ define void @use() nounwind {
 
   ret void
 }
+
+; CHECK: _fp:
+; CHECK-NEXT: .long _fun
+ at fp = constant void ()* @fun

Added: llvm/trunk/test/Object/dllimport.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Object/dllimport.ll?rev=239560&view=auto
==============================================================================
--- llvm/trunk/test/Object/dllimport.ll (added)
+++ llvm/trunk/test/Object/dllimport.ll Thu Jun 11 16:42:18 2015
@@ -0,0 +1,17 @@
+; RUN: llvm-as %s -o - | llvm-nm - | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; CHECK: U __imp_f
+; CHECK: U __imp_v
+; CHECK: T g
+
+declare dllimport void @f()
+ at v = external dllimport global i32
+
+define void @g() {
+  call void @f()
+  store i32 42, i32* @v
+  ret void
+}