[llvm][support] Replace `std::vector<bool>` use in YAMLTraits

[jansvoboda11]

Summary

LLVM Programmer’s Manual strongly discourages the use of std::vector<bool> and suggests llvm::BitVector as a possible replacement.

This patch replaces the use of std::vector with llvm::BitVector in LLVM's YAML traits and replaces the call to Vec.insert(Vec.begin(), N, false) on empty Vec with Vec.resize(N, false), which has the same sematnics but avoids using insert and iterators, which llvm::BitVector doesn't possess.

[dblaikie]

SGTM!

[dexonsmith]

LGTM, with an alternative inline.

llvm/lib/Support/YAMLTraits.cpp

302

I might drop the explicit false parameter, since it feels implied to me (and very slightly noisy), but up to you.

[mehdi_amini]

llvm/include/llvm/Support/YAMLTraits.h

34

Is the <vector> header still needed then?

[jansvoboda11]

llvm/include/llvm/Support/YAMLTraits.h

34

Yes, see the rest of the diff.

llvm/include/llvm/Support/YAMLTraits.h

 //===- llvm/Support/YAMLTraits.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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_YAMLTRAITS_H
 #define LLVM_SUPPORT_YAMLTRAITS_H
 
+#include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/YAMLParser.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cctype>
 #include <map>
 #include <memory>
 #include <new>
 #include <string>
 #include <system_error>
 #include <type_traits>
 #include <vector>
 
 namespace llvm {
 
 class VersionTuple;
 
 namespace yaml {
 
 enum class NodeKind : uint8_t {

 
 private:
   SourceMgr                           SrcMgr; // must be before Strm
   std::unique_ptr<llvm::yaml::Stream> Strm;
   std::unique_ptr<HNode>              TopNode;
   std::error_code                     EC;
   BumpPtrAllocator                    StringAllocator;
   document_iterator                   DocIterator;
-  std::vector<bool>                   BitValuesUsed;
+  llvm::BitVector                     BitValuesUsed;
   HNode *CurrentNode = nullptr;
   bool                                ScalarMatchFound = false;
   bool AllowUnknownKeys = false;
 };
 
 ///
 /// The Output class is used to generate a yaml document from in-memory structs
 /// and vectors.

llvm/lib/Support/YAMLTraits.cpp

void Input::endEnumScalar() {
   if (!ScalarMatchFound) {
     setError(CurrentNode, "unknown enumerated scalar");
   }
 }
 
 bool Input::beginBitSetScalar(bool &DoClear) {
   BitValuesUsed.clear();
   if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode)) {
-    BitValuesUsed.insert(BitValuesUsed.begin(), SQ->Entries.size(), false);
+    BitValuesUsed.resize(SQ->Entries.size());
   } else {
     setError(CurrentNode, "expected sequence of bit values");
   }
   DoClear = true;
   return true;
 }
 
 bool Input::bitSetMatch(const char *Str, bool) {