[PATCH] ms-inline-asm: Add facilities for rewriting labels in X86AsmParser

[Reid Kleckner]

================
Comment at: include/llvm/MC/MCParser/MCAsmParser.h:57
@@ -54,2 +56,3 @@
                                           bool IsUnevaluatedContext) = 0;
+  virtual void LookupInlineAsmLabel(StringRef &Identifier, SourceMgr &SM, SMLoc Location) = 0;
 
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It's generally nicer to avoid having API breakage between LLVM in clang if it can be avoided.  In this case, I'd give this a no-op implementation that clang overrides instead of a pure virtual method which will break the clang build for a few revisions when this lands.

================
Comment at: lib/MC/MCParser/AsmParser.cpp:4620
@@ +4619,3 @@
+    case AOK_Identifier:
+      OS << AR.Identifier;
+      break;
----------------
This should really be making an local label that doesn't make it into the object file.  MC should know what the local label prefix is.  It's usually 'L', I think.

If you add the prefix here, then maybe this should be AOK_Label or something.

================
Comment at: lib/Target/X86/AsmParser/X86AsmParser.cpp:1305
@@ +1304,3 @@
+
+  // If the identifier lookup was unsuccessful, assume that we are dealing with
+  // a label.
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What does MSVC do in this case?  I assume it uses the opposite logic for this code:

  void foo();
  void __declspec(naked) bar() {
    __asm {
    foo:
      jmp foo ; probably infinite loops instead of tail calling bar.
    }
  }

I guess this is the hard case:

  void foo();
  void __declspec(naked) bar() {
    __asm {
      test ecx, ecx
      xor eax, eax
      jz foo
      mov eax 1
  foo:
     ret
  }

http://reviews.llvm.org/D4587