[Mangle] Add flag to asm labels to disable '\01' prefixing

LLDB synthesizes decls using asm labels. These decls cannot have a mangle
different than the one specified in the label name. I.e., the '\01' prefix
should not be added.

Fixes an expression evaluation failure in lldb's TestVirtual.py on iOS.

rdar://45827323

Differential Revision: https://reviews.llvm.org/D67774

llvm-svn: 372903
diff --git a/clang/unittests/AST/DeclTest.cpp b/clang/unittests/AST/DeclTest.cpp
index 6691952..b3bc064 100644
--- a/clang/unittests/AST/DeclTest.cpp
+++ b/clang/unittests/AST/DeclTest.cpp
@@ -10,12 +10,16 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Mangle.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Basic/LLVM.h"
 #include "clang/Tooling/Tooling.h"
 #include "gtest/gtest.h"
 
 using namespace clang::ast_matchers;
 using namespace clang::tooling;
+using namespace clang;
 
 TEST(Decl, CleansUpAPValues) {
   MatchFinder Finder;
@@ -56,3 +60,48 @@
       "constexpr _Complex __uint128_t c = 0xffffffffffffffff;",
       Args));
 }
+
+TEST(Decl, AsmLabelAttr) {
+  // Create two method decls: `f` and `g`.
+  StringRef Code = R"(
+    struct S {
+      void f() {}
+      void g() {}
+    };
+  )";
+  auto AST =
+      tooling::buildASTFromCodeWithArgs(Code, {"-target", "i386-apple-darwin"});
+  ASTContext &Ctx = AST->getASTContext();
+  assert(Ctx.getTargetInfo().getDataLayout().getGlobalPrefix() &&
+         "Expected target to have a global prefix");
+  DiagnosticsEngine &Diags = AST->getDiagnostics();
+  SourceManager &SM = AST->getSourceManager();
+  FileID MainFileID = SM.getMainFileID();
+
+  // Find the method decls within the AST.
+  SmallVector<Decl *, 1> Decls;
+  AST->findFileRegionDecls(MainFileID, Code.find('{'), 0, Decls);
+  ASSERT_TRUE(Decls.size() == 1);
+  CXXRecordDecl *DeclS = cast<CXXRecordDecl>(Decls[0]);
+  NamedDecl *DeclF = *DeclS->method_begin();
+  NamedDecl *DeclG = *(++DeclS->method_begin());
+
+  // Attach asm labels to the decls: one literal, and one not.
+  DeclF->addAttr(::new (Ctx) AsmLabelAttr(Ctx, SourceLocation(), "foo",
+                                          /*LiteralLabel=*/true));
+  DeclG->addAttr(::new (Ctx) AsmLabelAttr(Ctx, SourceLocation(), "goo",
+                                          /*LiteralLabel=*/false));
+
+  // Mangle the decl names.
+  std::string MangleF, MangleG;
+  MangleContext *MC = ItaniumMangleContext::create(Ctx, Diags);
+  {
+    llvm::raw_string_ostream OS_F(MangleF);
+    llvm::raw_string_ostream OS_G(MangleG);
+    MC->mangleName(DeclF, OS_F);
+    MC->mangleName(DeclG, OS_G);
+  }
+
+  ASSERT_TRUE(0 == MangleF.compare("\x01" "foo"));
+  ASSERT_TRUE(0 == MangleG.compare("goo"));
+}