[demangler] Resync demangler sources

[urnathan]

Summary

ChuanqiXu noticed that D117879 contained some unintended changes. Serge's recent patches to llvm/include/llvm/Demangle didn't also change libcxxabi/src/Demangle, which is the canonical source location. This resyncs those commits to the libcxxabi directory.

Commits:

• 1f9e18b6565fd1bb69c4b649b9efd3467b3c7c7d
• f53d359816e66a107195e1e4b581e2a33bbafaa4
• 065044c443f4041f32e0a8d6e633f9d92580fbca

I'll update D117879 shortly

[urnathan]

I missed the ItaniumDemangle.h #include changes.

libcxxabi/src/demangle/ItaniumDemangle.h

 
 // FIXME: (possibly) incomplete list of features that clang mangles that this
 // file does not yet support:
 //   - C++ modules TS
 
 #include "DemangleConfig.h"
 #include "StringView.h"
 #include "Utility.h"
+#include <algorithm>
 #include <cassert>
 #include <cctype>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
-#include <numeric>
+#include <limits>
 #include <utility>
 
 #define FOR_EACH_NODE_KIND(X) \
     X(NodeArrayNode) \
     X(DotSuffix) \
     X(VendorExtQualType) \
     X(QualType) \
     X(ConversionOperatorType) \

libcxxabi/src/demangle/StringView.h

 //===--- StringView.h -------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // FIXME: Use std::string_view instead when we support C++17.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef DEMANGLE_STRINGVIEW_H
 #define DEMANGLE_STRINGVIEW_H
 
 #include "DemangleConfig.h"
-#include <algorithm>
 #include <cassert>
 #include <cstring>
 
 DEMANGLE_NAMESPACE_BEGIN
 
 class StringView {
   const char *First;
   const char *Last;
 
 public:
   static const size_t npos = ~size_t(0);
 
   template <size_t N>
   StringView(const char (&Str)[N]) : First(Str), Last(Str + N - 1) {}
   StringView(const char *First_, const char *Last_)
       : First(First_), Last(Last_) {}
   StringView(const char *First_, size_t Len)
       : First(First_), Last(First_ + Len) {}
   StringView(const char *Str) : First(Str), Last(Str + std::strlen(Str)) {}
   StringView() : First(nullptr), Last(nullptr) {}
 
   StringView substr(size_t Pos, size_t Len = npos) const {
     assert(Pos <= size());
-    return StringView(begin() + Pos, std::min(Len, size() - Pos));
+    if (Len > size() - Pos)
+      Len = size() - Pos;
+    return StringView(begin() + Pos, Len);
   }
 
   size_t find(char C, size_t From = 0) const {
-    size_t FindBegin = std::min(From, size());
     // Avoid calling memchr with nullptr.
-    if (FindBegin < size()) {
+    if (From < size()) {
       // Just forward to memchr, which is faster than a hand-rolled loop.
-      if (const void *P = ::memchr(First + FindBegin, C, size() - FindBegin))
+      if (const void *P = ::memchr(First + From, C, size() - From))
         return size_t(static_cast<const char *>(P) - First);
     }
     return npos;
   }
 
   StringView dropFront(size_t N = 1) const {
     if (N >= size())
       N = size();
bool consumeFront(StringView S) {
     return true;
   }
 
   bool startsWith(char C) const { return !empty() && *begin() == C; }
 
   bool startsWith(StringView Str) const {
     if (Str.size() > size())
       return false;
-    return std::equal(Str.begin(), Str.end(), begin());
+    return std::strncmp(Str.begin(), begin(), Str.size()) == 0;
   }
 
   const char &operator[](size_t Idx) const { return *(begin() + Idx); }
 
   const char *begin() const { return First; }
   const char *end() const { return Last; }
   size_t size() const { return static_cast<size_t>(Last - First); }
   bool empty() const { return First == Last; }
 };
 
 inline bool operator==(const StringView &LHS, const StringView &RHS) {
   return LHS.size() == RHS.size() &&
-         std::equal(LHS.begin(), LHS.end(), RHS.begin());
+         std::strncmp(LHS.begin(), RHS.begin(), LHS.size()) == 0;
 }
 
 DEMANGLE_NAMESPACE_END
 
 #endif

libcxxabi/src/demangle/Utility.h

 //===--- Utility.h ----------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // Provide some utility classes for use in the demangler(s).
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef DEMANGLE_UTILITY_H
 #define DEMANGLE_UTILITY_H
 
 #include "StringView.h"
+#include <array>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
-#include <iterator>
+#include <exception>
 #include <limits>
 
 DEMANGLE_NAMESPACE_BEGIN
 
 // Stream that AST nodes write their string representation into after the AST
 // has been parsed.
 class OutputBuffer {
   char *Buffer = nullptr;
class OutputBuffer {
 
   void writeUnsigned(uint64_t N, bool isNeg = false) {
     // Handle special case...
     if (N == 0) {
       *this << '0';
       return;
     }
 
-    char Temp[21];
-    char *TempPtr = std::end(Temp);
+    std::array<char, 21> Temp;
+    char *TempPtr = Temp.data() + Temp.size();
 
     while (N) {
       *--TempPtr = char('0' + N % 10);
       N /= 10;
     }
 
     // Add negative sign...
     if (isNeg)
       *--TempPtr = '-';
-    this->operator<<(StringView(TempPtr, std::end(Temp)));
+    this->operator<<(StringView(TempPtr, Temp.data() + Temp.size()));
   }
 
 public:
   OutputBuffer(char *StartBuf, size_t Size)
       : Buffer(StartBuf), CurrentPosition(0), BufferCapacity(Size) {}
   OutputBuffer() = default;
   void reset(char *Buffer_, size_t BufferCapacity_) {
     CurrentPosition = 0;