Add a Microsoft Demangler.

This adds initial support for a demangling library (LLVMDemangle)
and tool (llvm-undname) for demangling Microsoft names.  This
doesn't cover 100% of cases and there are some known limitations
which I intend to address in followup patches, at least until such
time that we have (near) 100% test coverage matching up with all
of the test cases in clang/test/CodeGenCXX/mangle-ms-*.

Differential Revision: https://reviews.llvm.org/D49552

llvm-svn: 337584

llvm/include/llvm/Demangle/Demangle.h

@@ -16,7 +16,7 @@ namespace llvm {
 /// The mangled_name is demangled into buf and returned. If the buffer is not
 /// large enough, realloc is used to expand it.
 ///
-/// The *status will be set to a value from the enumeration
+/// The *status will be set to a value from the following enumeration
 enum : int {
   demangle_unknown_error = -4,
   demangle_invalid_args = -3,
@@ -27,6 +27,8 @@ enum : int {
 
 char *itaniumDemangle(const char *mangled_name, char *buf, size_t *n,
                       int *status);
+char *microsoftDemangle(const char *mangled_name, char *buf, size_t *n,
+                        int *status);
 
 /// "Partial" demangler. This supports demangling a string into an AST
 /// (typically an intermediate stage in itaniumDemangle) and querying certain

llvm/lib/Demangle/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_llvm_library(LLVMDemangle
   ItaniumDemangle.cpp
-
+  MicrosoftDemangle.cpp
+
   ADDITIONAL_HEADER_DIRS
   "${LLVM_MAIN_INCLUDE_DIR}/llvm/Demangle"
 )