[MS Compat] Second try to fix quoting behavior of linker directives

[mkuper]

Summary

Apparently, MSVC behavior is somewhat surprising:
For #pragma comment(linker, ...) it expects the comment string to be quoted, but for #pragma comment(lib, ...) it quotes the library name.

So, these are legal:
#pragma comment(linker, "/DEFAULTLIB:\"foo bar.lib\"")
#pragma comment(lib, "foo bar.lib")
And these get rejected:
#pragma comment(linker, "/DEFAULTLIB:foo bar.lib")
#pragma comment(lib, "\"foo bar.lib\"")

[mkuper]

Accompanying clang patch here:
http://reviews.llvm.org/D7653

[rnk]

lgtm

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

emitModuleFlags(MCStreamer &Streamer,
   // Emit the linker options to the linker .drectve section.  According to the
   // spec, this section is a space-separated string containing flags for linker.
   const MCSection *Sec = getDrectveSection();
   Streamer.SwitchSection(Sec);
   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
-      StringRef Op = MDOption->getString();
       // Lead with a space for consistency with our dllexport implementation.
-      std::string Escaped(" ");
-      if (!Op.startswith("\"") && (Op.find(" ") != StringRef::npos)) {
-        // The PE-COFF spec says args with spaces must be quoted.  It doesn't say
-        // how to escape quotes, but it probably uses this algorithm:
-        // http://msdn.microsoft.com/en-us/library/17w5ykft(v=vs.85).aspx
-        // FIXME: Reuse escaping code from Support/Windows/Program.inc
-        Escaped.push_back('\"');
-        Escaped.append(Op);
-        Escaped.push_back('\"');
-      } else {
-        Escaped.append(Op);
-      }
-      Streamer.EmitBytes(Escaped);
+      std::string Directive(" ");
+      Directive.append(MDOption->getString());
+      Streamer.EmitBytes(Directive);
     }
   }
 }
 
 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
     unsigned Priority, const MCSymbol *KeySym) const {
   return getContext().getAssociativeCOFFSection(
       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
 }
 
 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
     unsigned Priority, const MCSymbol *KeySym) const {
   return getContext().getAssociativeCOFFSection(
       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
 }

test/MC/COFF/linker-options.ll

 ; RUN: llc -O0 -mtriple=i386-pc-win32 -filetype=asm -o - %s | FileCheck %s
 
-!0 = !{i32 6, !"Linker Options", !{!{!"/DEFAULTLIB:msvcrt.lib"}, !{!"/DEFAULTLIB:msvcrt.lib", !"/DEFAULTLIB:secur32.lib"}, !{!"/DEFAULTLIB:C:\5Cpath to\5Casan_rt.lib"}, !{!"/with spaces"}, !{!"\22/quoted spaces\22"}}}
+!0 = !{i32 6, !"Linker Options", !{!{!"/DEFAULTLIB:msvcrt.lib"}, !{!"/DEFAULTLIB:msvcrt.lib", !"/DEFAULTLIB:secur32.lib"}, !{!"/DEFAULTLIB:\22C:\5Cpath to\5Casan_rt.lib\22"}, !{!"\22/with spaces\22"}}}
 
 !llvm.module.flags = !{ !0 }
 
 define dllexport void @foo() {
   ret void
 }
 
 ; CHECK: .section        .drectve,"yn"
 ; CHECK: .ascii   " /DEFAULTLIB:msvcrt.lib"
 ; CHECK: .ascii   " /DEFAULTLIB:msvcrt.lib"
 ; CHECK: .ascii   " /DEFAULTLIB:secur32.lib"
-; CHECK: .ascii   " \"/DEFAULTLIB:C:\\path to\\asan_rt.lib\""
+; CHECK: .ascii   " /DEFAULTLIB:\"C:\\path to\\asan_rt.lib\""
 ; CHECK: .ascii   " \"/with spaces\""
-; CHECK: .ascii   " \"/quoted spaces\""
 ; CHECK: .ascii   " /EXPORT:_foo"