ms-inline-asm: Correctly mark MS inline ASM labels as used

[• ehsan]

Summary

This fixes PR21155.

[rnk]

lgtm

[• ehsan]

Closed by commit rL219322 (authored by @ehsan).

lib/Sema/SemaStmtAsm.cpp

 }
 
 LabelDecl *Sema::GetOrCreateMSAsmLabel(StringRef ExternalLabelName,
                                        SourceLocation Location,
                                        bool AlwaysCreate) {
   LabelDecl* Label = LookupOrCreateLabel(PP.getIdentifierInfo(ExternalLabelName),
                                          Location);
 
-  if (!Label->isMSAsmLabel()) {
+  if (Label->isMSAsmLabel()) {
+    // If we have previously created this label implicitly, mark it as used.
+    Label->markUsed(Context);
+  } else {
     // Otherwise, insert it, but only resolve it if we have seen the label itself.
     std::string InternalName;
     llvm::raw_string_ostream OS(InternalName);
     // Create an internal name for the label.  The name should not be a valid mangled
     // name, and should be unique.  We use a dot to make the name an invalid mangled
     // name.
     OS << "__MSASMLABEL_." << MSAsmLabelNameCounter++ << "__" << ExternalLabelName;
     Label->setMSAsmLabel(OS.str());

test/Sema/ms-inline-asm.c

 // REQUIRES: x86-registered-target
-// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -fasm-blocks -Wno-microsoft -verify -fsyntax-only
+// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -fasm-blocks -Wno-microsoft -Wunused-label -verify -fsyntax-only
 
 void t1(void) { 
  __asm __asm // expected-error {{__asm used with no assembly instructions}}
 }
 
 void f() {
   int foo;
   __asm { 

 void t10() {
   goto foo; // expected-error {{cannot jump from this goto statement to label 'foo' inside an inline assembly block}}
   __asm foo: // expected-note {{inline assembly label 'foo' declared here}}
   __asm mov eax, 0
 }
 
 void t11() {
 foo:
-  __asm mov eax, foo // expected-error {{use of undeclared label 'foo'}}
+  __asm mov eax, foo // expected-error {{use of undeclared label 'foo'}} expected-warning {{unused label 'foo'}}
+}
+
+void t12() {
+  __asm foo:
+  __asm bar: // expected-warning {{unused label 'bar'}}
+  __asm jmp foo
 }