[llvm] annotate interfaces in Demangle for DLL export (llvm#147564)

## Purpose

This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the `Demangle` interface with
a new `DEMANGLE_ABI` annotation, which behaves like the `LLVM_ABI`. This
annotation currently has no meaningful impact on the LLVM build;
however, it is a prerequisite to support an LLVM Windows DLL (shared
library) build.

## Overview

1. Add a new `Demangle/Visibility.h` header file that defines a new
`DEMANGLE_ABI` macro. The macro resolves to the proper DLL export/import
annotation on Windows and a "default" visibility annotation elsewhere.
2. Add a new `LLVM_ENABLE_DEMANGLE_EXPORT_ANNOTATIONS ` `#cmakedefine`
that is used to gate the definition of `DEMANGLE_ABI`.
3. Code-mod annotate the public `Demangle` interface using the
[Interface Definition Scanner (IDS)](https://github.com/compnerd/ids)
tool.
4. Manually fix-up `#include` statements for consistency.
5. Format the changes with `clang-format`.
6. Add a "stub" version of `Visibility.h` under `libcxxabi/src/demangle`
that always defines `DEMANGLE_ABI` to nothing.
7. Update the canonical `libcxxabi/src/demangle/ItaniumDemangle.h`
instead of the llvm copy, and run `cp-to-llvm.sh` to ensure the llvm
copy matches. NOTE: we rely on `ccp-to-llvm.sh` not copying
`Visibillity.h` as is already the case for `DemangleConfig.h`.

## Background

This PR follows the pattern established with the `llvm-c` changes made
in llvm#141701.

This effort is tracked in llvm#109483. Additional context is provided in
[this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307),
and documentation for `LLVM_ABI` and related annotations is found in the
LLVM repo
[here](https://github.com/llvm/llvm-project/blob/main/llvm/docs/InterfaceExportAnnotations.rst).

## Validation

Local builds and tests to validate cross-platform compatibility. This
included llvm, clang, and lldb on the following configurations:

- Windows with MSVC
- Windows with Clang
- Linux with GCC
- Linux with Clang
- Darwin with Clang

---------

Co-authored-by: Louis Dionne <[email protected]>

Author: andrurogerz

libcxxabi/src/demangle/DemangleConfig.h

@@ -115,4 +115,8 @@
 #define DEMANGLE_NAMESPACE_BEGIN namespace { namespace itanium_demangle {
 #define DEMANGLE_NAMESPACE_END } }
 
+// The DEMANGLE_ABI macro resolves to nothing when building libc++abi. Only
+// the llvm copy defines DEMANGLE_ABI as a visibility attribute.
+#define DEMANGLE_ABI
+
 #endif // LIBCXXABI_DEMANGLE_DEMANGLE_CONFIG_H

libcxxabi/src/demangle/ItaniumDemangle.h

@@ -3049,7 +3049,8 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
   Node *parse(bool ParseParams = true);
 };
 
-const char* parse_discriminator(const char* first, const char* last);
+DEMANGLE_ABI const char *parse_discriminator(const char *first,
+                                             const char *last);
 
 // <name> ::= <nested-name> // N
 //        ::= <local-name> # See Scope Encoding below  // Z

llvm/include/llvm/Demangle/Demangle.h

@@ -9,6 +9,7 @@
 #ifndef LLVM_DEMANGLE_DEMANGLE_H
 #define LLVM_DEMANGLE_DEMANGLE_H
 
+#include "DemangleConfig.h"
 #include <cstddef>
 #include <optional>
 #include <string>
@@ -33,7 +34,8 @@ enum : int {
 /// Returns a non-NULL pointer to a NUL-terminated C style string
 /// that should be explicitly freed, if successful. Otherwise, may return
 /// nullptr if mangled_name is not a valid mangling or is nullptr.
-char *itaniumDemangle(std::string_view mangled_name, bool ParseParams = true);
+DEMANGLE_ABI char *itaniumDemangle(std::string_view mangled_name,
+                                   bool ParseParams = true);
 
 enum MSDemangleFlags {
   MSDF_None = 0,
@@ -52,87 +54,90 @@ enum MSDemangleFlags {
 /// bytes of the input string were consumed.
 /// status receives one of the demangle_ enum entries above if it's not nullptr.
 /// Flags controls various details of the demangled representation.
-char *microsoftDemangle(std::string_view mangled_name, size_t *n_read,
-                        int *status, MSDemangleFlags Flags = MSDF_None);
+DEMANGLE_ABI char *microsoftDemangle(std::string_view mangled_name,
+                                     size_t *n_read, int *status,
+                                     MSDemangleFlags Flags = MSDF_None);
 
-std::optional<size_t>
+DEMANGLE_ABI std::optional<size_t>
 getArm64ECInsertionPointInMangledName(std::string_view MangledName);
 
 // Demangles a Rust v0 mangled symbol.
-char *rustDemangle(std::string_view MangledName);
+DEMANGLE_ABI char *rustDemangle(std::string_view MangledName);
 
 // Demangles a D mangled symbol.
-char *dlangDemangle(std::string_view MangledName);
+DEMANGLE_ABI char *dlangDemangle(std::string_view MangledName);
 
 /// Attempt to demangle a string using different demangling schemes.
 /// The function uses heuristics to determine which demangling scheme to use.
 /// \param MangledName - reference to string to demangle.
 /// \returns - the demangled string, or a copy of the input string if no
 /// demangling occurred.
-std::string demangle(std::string_view MangledName);
+DEMANGLE_ABI std::string demangle(std::string_view MangledName);
 
-bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result,
-                          bool CanHaveLeadingDot = true,
-                          bool ParseParams = true);
+DEMANGLE_ABI bool nonMicrosoftDemangle(std::string_view MangledName,
+                                       std::string &Result,
+                                       bool CanHaveLeadingDot = true,
+                                       bool ParseParams = true);
 
 /// "Partial" demangler. This supports demangling a string into an AST
 /// (typically an intermediate stage in itaniumDemangle) and querying certain
 /// properties or partially printing the demangled name.
 struct ItaniumPartialDemangler {
-  ItaniumPartialDemangler();
+  DEMANGLE_ABI ItaniumPartialDemangler();
 
-  ItaniumPartialDemangler(ItaniumPartialDemangler &&Other);
-  ItaniumPartialDemangler &operator=(ItaniumPartialDemangler &&Other);
+  DEMANGLE_ABI ItaniumPartialDemangler(ItaniumPartialDemangler &&Other);
+  DEMANGLE_ABI ItaniumPartialDemangler &
+  operator=(ItaniumPartialDemangler &&Other);
 
   /// Demangle into an AST. Subsequent calls to the rest of the member functions
   /// implicitly operate on the AST this produces.
   /// \return true on error, false otherwise
-  bool partialDemangle(const char *MangledName);
+  DEMANGLE_ABI bool partialDemangle(const char *MangledName);
 
   /// Just print the entire mangled name into Buf. Buf and N behave like the
   /// second and third parameters to __cxa_demangle.
-  char *finishDemangle(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *finishDemangle(char *Buf, size_t *N) const;
 
   /// See \ref finishDemangle
   ///
   /// \param[in] OB A llvm::itanium_demangle::OutputBuffer that the demangled
   /// name will be printed into.
   ///
-  char *finishDemangle(void *OB) const;
+  DEMANGLE_ABI char *finishDemangle(void *OB) const;
 
   /// Get the base name of a function. This doesn't include trailing template
   /// arguments, ie for "a::b<int>" this function returns "b".
-  char *getFunctionBaseName(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *getFunctionBaseName(char *Buf, size_t *N) const;
 
   /// Get the context name for a function. For "a::b::c", this function returns
   /// "a::b".
-  char *getFunctionDeclContextName(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *getFunctionDeclContextName(char *Buf, size_t *N) const;
 
   /// Get the entire name of this function.
-  char *getFunctionName(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *getFunctionName(char *Buf, size_t *N) const;
 
   /// Get the parameters for this function.
-  char *getFunctionParameters(char *Buf, size_t *N) const;
-  char *getFunctionReturnType(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *getFunctionParameters(char *Buf, size_t *N) const;
+  DEMANGLE_ABI char *getFunctionReturnType(char *Buf, size_t *N) const;
 
   /// If this function has any cv or reference qualifiers. These imply that
   /// the function is a non-static member function.
-  bool hasFunctionQualifiers() const;
+  DEMANGLE_ABI bool hasFunctionQualifiers() const;
 
   /// If this symbol describes a constructor or destructor.
-  bool isCtorOrDtor() const;
+  DEMANGLE_ABI bool isCtorOrDtor() const;
 
   /// If this symbol describes a function.
-  bool isFunction() const;
+  DEMANGLE_ABI bool isFunction() const;
 
   /// If this symbol describes a variable.
-  bool isData() const;
+  DEMANGLE_ABI bool isData() const;
 
   /// If this symbol is a <special-name>. These are generally implicitly
   /// generated by the implementation, such as vtables and typeinfo names.
-  bool isSpecialName() const;
+  DEMANGLE_ABI bool isSpecialName() const;
 
-  ~ItaniumPartialDemangler();
+  DEMANGLE_ABI ~ItaniumPartialDemangler();
 
 private:
   void *RootNode;

llvm/include/llvm/Demangle/DemangleConfig.h

@@ -94,4 +94,24 @@
 #define DEMANGLE_NAMESPACE_BEGIN namespace llvm { namespace itanium_demangle {
 #define DEMANGLE_NAMESPACE_END } }
 
+/// DEMANGLE_ABI is the export/visibility macro used to mark symbols delcared in
+/// llvm/Demangle as exported when built as a shared library.
+#if defined(LLVM_BUILD_STATIC) || !defined(LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS)
+#define DEMANGLE_ABI
+#else
+#if defined(_WIN32)
+#if defined(LLVM_EXPORTS)
+#define DEMANGLE_ABI __declspec(dllexport)
+#else
+#define DEMANGLE_ABI__declspec(dllimport)
+#endif
+#else
+#if __has_attribute(visibility)
+#define DEMANGLE_ABI __attribute__((__visibility__("default")))
+#else
+#define DEMANGLE_ABI
+#endif
+#endif
+#endif
+
 #endif

llvm/include/llvm/Demangle/ItaniumDemangle.h

@@ -3049,7 +3049,8 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
   Node *parse(bool ParseParams = true);
 };
 
-const char* parse_discriminator(const char* first, const char* last);
+DEMANGLE_ABI const char *parse_discriminator(const char *first,
+                                             const char *last);
 
 // <name> ::= <nested-name> // N
 //        ::= <local-name> # See Scope Encoding below  // Z

llvm/include/llvm/Demangle/MicrosoftDemangle.h

@@ -10,6 +10,7 @@
 #define LLVM_DEMANGLE_MICROSOFTDEMANGLE_H
 
 #include "llvm/Demangle/Demangle.h"
+#include "llvm/Demangle/DemangleConfig.h"
 #include "llvm/Demangle/MicrosoftDemangleNodes.h"
 
 #include <cassert>
@@ -151,14 +152,14 @@ class Demangler {
 
   // You are supposed to call parse() first and then check if error is true.  If
   // it is false, call output() to write the formatted name to the given stream.
-  SymbolNode *parse(std::string_view &MangledName);
+  DEMANGLE_ABI SymbolNode *parse(std::string_view &MangledName);
 
-  TagTypeNode *parseTagUniqueName(std::string_view &MangledName);
+  DEMANGLE_ABI TagTypeNode *parseTagUniqueName(std::string_view &MangledName);
 
   // True if an error occurred.
   bool Error = false;
 
-  void dumpBackReferences();
+  DEMANGLE_ABI void dumpBackReferences();
 
 private:
   SymbolNode *demangleEncodedSymbol(std::string_view &MangledName,