From 82e657b509b33611620076ab8065cb485b54c348 Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Thu, 11 Jun 2015 21:42:18 +0000
Subject: [PATCH] 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

llvm-svn: 239560
---
 llvm/lib/Object/IRObjectFile.cpp   |  3 +++
 llvm/test/CodeGen/X86/dllimport.ll |  4 ++++
 llvm/test/Object/dllimport.ll      | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 llvm/test/Object/dllimport.ll

diff --git a/llvm/lib/Object/IRObjectFile.cpp b/llvm/lib/Object/IRObjectFile.cpp
index e89cb8e..b3d5db8 100644
--- a/llvm/lib/Object/IRObjectFile.cpp
+++ b/llvm/lib/Object/IRObjectFile.cpp
@@ -198,6 +198,9 @@ std::error_code IRObjectFile::printSymbolName(raw_ostream &OS,
     return std::error_code();
   }
 
+  if (GV->hasDLLImportStorageClass())
+    OS << "__imp_";
+
   if (Mang)
     Mang->getNameWithPrefix(OS, GV, false);
   else
diff --git a/llvm/test/CodeGen/X86/dllimport.ll b/llvm/test/CodeGen/X86/dllimport.ll
index 9db654f..34faaeb 100644
--- a/llvm/test/CodeGen/X86/dllimport.ll
+++ b/llvm/test/CodeGen/X86/dllimport.ll
@@ -57,3 +57,7 @@ define void @use() nounwind {
 
   ret void
 }
+
+; CHECK: _fp:
+; CHECK-NEXT: .long _fun
+@fp = constant void ()* @fun
diff --git a/llvm/test/Object/dllimport.ll b/llvm/test/Object/dllimport.ll
new file mode 100644
index 0000000..afdb456
--- /dev/null
+++ b/llvm/test/Object/dllimport.ll
@@ -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()
+@v = external dllimport global i32
+
+define void @g() {
+  call void @f()
+  store i32 42, i32* @v
+  ret void
+}
-- 
2.7.4