X86: Do not produce GOT relocations on windows

[MatzeB]

Summary

r270209 ("Refactor X86 symbol access classification.") broke some EFI firmware projects targetting x86_64-pc-windows-macho. This patch fixes that:

Windows has no GOT relocations the way elf/darwin has.
"x86_64-pc-win32-macho" is sometimes used to build EFI firmware; Use windows style reloction (no-GOT) for this target.

[majnemer]

LGTM

llvm/trunk/lib/Target/TargetMachine.cpp

bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
                                          const GlobalValue *GV) const {
   Reloc::Model RM = getRelocationModel();
   const Triple &TT = getTargetTriple();
 
   // DLLImport explicitly marks the GV as external.
   if (GV && GV->hasDLLImportStorageClass())
     return false;
 
-  // Every other GV is local on COFF
-  if (TT.isOSBinFormatCOFF())
+  // Every other GV is local on COFF.
+  // Make an exception for windows OS in the triple: Some firmwares builds use
+  // *-win32-macho triples. This (accidentally?) produced windows relocations
+  // without GOT tables in older clang versions; Keep this behaviour.
+  if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
     return true;
 
   if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility()))
     return true;
 
   if (TT.isOSBinFormatMachO()) {
     if (RM == Reloc::Static)
       return true;

llvm/trunk/test/CodeGen/X86/x86-64-pic-12.ll

+; RUN: llc -o - %s -relocation-model=pic | FileCheck %s
+; Check that we do not get GOT relocations with the x86_64-pc-windows-macho
+; triple.
+target triple = "x86_64-pc-windows-macho"
+
+@g = common global i32 0, align 4
+
+declare i32 @extbar()
+
+; CHECK-LABEL: bar:
+; CHECK: callq _extbar
+; CHECK: leaq _extbar(%rip),
+; CHECK-NOT: @GOT
+define i8* @bar() {
+  call i32 @extbar()
+  ret i8* bitcast (i32 ()* @extbar to i8*)
+}
+
+; CHECK-LABEL: foo:
+; CHECK: callq _bar
+; CHECK: movl _g(%rip),
+; CHECK-NOT: @GOT
+define i32 @foo() {
+  call i8* @bar()
+  %gval = load i32, i32* @g, align 4
+  ret i32 %gval
+}