[COFF] Use COFF stubs for extern_weak functions

Summary:
A COFF stub indirects the reference to a symbol through memory. A
.refptr.$sym global variable pointer is created to refer to $sym.
Typically mingw uses these for external global variable declarations,
but we can use them for weak function declarations as well.

Updates the dso_local classification to add a special case for
extern_weak symbols on COFF in both clang and LLVM.

Fixes PR37598

Reviewers: smeenai, mstorsjo

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D61615

llvm-svn: 360207

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 80dcd74a5d2..6fca1acb009 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -3503,8 +3503,9 @@ bool X86FastISel::fastLowerCall(CallLoweringInfo &CLI) {
 
     // This will be a direct call, or an indirect call through memory for
     // NonLazyBind calls or dllimport calls.
-    bool NeedLoad =
-        OpFlags == X86II::MO_DLLIMPORT || OpFlags == X86II::MO_GOTPCREL;
+    bool NeedLoad = OpFlags == X86II::MO_DLLIMPORT ||
+                    OpFlags == X86II::MO_GOTPCREL ||
+                    OpFlags == X86II::MO_COFFSTUB;
     unsigned CallOpc = NeedLoad
                            ? (Is64Bit ? X86::CALL64m : X86::CALL32m)
                            : (Is64Bit ? X86::CALL64pcrel32 : X86::CALLpcrel32);