[NFC] Move FoldingSetNodeIDRef::ComputeHash and FoldingSetNodeID::ComputeHash definitions to header

[yurai007]

Summary

Lack of ComputeHash inlining slows down slightly FoldingSetBase::FindNodeOrInsertPos calls.
Inlining makes it faster which matters in particular for FoldingSet users in ASTContext.

Extracted from: https://reviews.llvm.org/D118385

[serge-sans-paille]

Not a big fan of moving Hashing.h to the header, but performance >> compilation time, so I'm fine with that patch (backed by the benchmark @nikic ran https://reviews.llvm.org/D118385#3281620)

[aeubanks]

if you want the most performance, shouldn't you be building with ThinLTO -DLLVM_ENABLE_LTO=Thin? or is this helping even with LTO?

[yurai007]

In D118612#3290697, @aeubanks wrote:

if you want the most performance, shouldn't you be building with ThinLTO -DLLVM_ENABLE_LTO=Thin? or is this helping even with LTO?

We discussed LTO topic a bit here: https://reviews.llvm.org/D118385#3278901 On my local build I can use LTO but in general not all distros enable it for Clang/LLVM packages. I'm not sure whether change would give any gains on top of LTO build.

llvm/include/llvm/ADT/FoldingSet.h

 /// in a graph.  This code was originally created by Chris Lattner for use with
 /// SelectionDAGCSEMap, but was isolated to provide use across the llvm code
 /// set.
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_FOLDINGSET_H
 #define LLVM_ADT_FOLDINGSET_H
 
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/Support/Allocator.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <utility>
 
class FoldingSetNodeIDRef {
   size_t Size = 0;
 
 public:
   FoldingSetNodeIDRef() = default;
   FoldingSetNodeIDRef(const unsigned *D, size_t S) : Data(D), Size(S) {}
 
   /// ComputeHash - Compute a strong hash value for this FoldingSetNodeIDRef,
   /// used to lookup the node in the FoldingSetBase.
-  unsigned ComputeHash() const;
+  unsigned ComputeHash() const {
+    return static_cast<unsigned>(hash_combine_range(Data, Data + Size));
+  }
 
   bool operator==(FoldingSetNodeIDRef) const;
 
   bool operator!=(FoldingSetNodeIDRef RHS) const { return !(*this == RHS); }
 
   /// Used to compare the "ordering" of two nodes as defined by the
   /// profiled bits and their ordering defined by memcmp().
   bool operator<(FoldingSetNodeIDRef) const;
public:
   inline void Add(const T &x) { FoldingSetTrait<T>::Profile(x, *this); }
 
   /// clear - Clear the accumulated profile, allowing this FoldingSetNodeID
   /// object to be used to compute a new profile.
   inline void clear() { Bits.clear(); }
 
   /// ComputeHash - Compute a strong hash value for this FoldingSetNodeID, used
   /// to lookup the node in the FoldingSetBase.
-  unsigned ComputeHash() const;
+  unsigned ComputeHash() const {
+    return FoldingSetNodeIDRef(Bits.data(), Bits.size()).ComputeHash();
+  }
 
   /// operator== - Used to compare two nodes to each other.
   bool operator==(const FoldingSetNodeID &RHS) const;
   bool operator==(const FoldingSetNodeIDRef RHS) const;
 
   bool operator!=(const FoldingSetNodeID &RHS) const { return !(*this == RHS); }
   bool operator!=(const FoldingSetNodeIDRef RHS) const { return !(*this ==RHS);}
 

llvm/lib/Support/FoldingSet.cpp

 //===-- Support/FoldingSet.cpp - Uniquing Hash Set --------------*- 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements a hash set that can be used to remove duplication of
 // nodes in a graph.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/FoldingSet.h"
-#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MathExtras.h"
 #include <cassert>
 #include <cstring>
 using namespace llvm;
 
 //===----------------------------------------------------------------------===//
 // FoldingSetNodeIDRef Implementation
 
-/// ComputeHash - Compute a strong hash value for this FoldingSetNodeIDRef,
-/// used to lookup the node in the FoldingSetBase.
-unsigned FoldingSetNodeIDRef::ComputeHash() const {
-  return static_cast<unsigned>(hash_combine_range(Data, Data+Size));
-}
-
 bool FoldingSetNodeIDRef::operator==(FoldingSetNodeIDRef RHS) const {
   if (Size != RHS.Size) return false;
   return memcmp(Data, RHS.Data, Size*sizeof(*Data)) == 0;
 }
 
 /// Used to compare the "ordering" of two nodes as defined by the
 /// profiled bits and their ordering defined by memcmp().
 bool FoldingSetNodeIDRef::operator<(FoldingSetNodeIDRef RHS) const {
void FoldingSetNodeID::AddString(StringRef String) {
   Bits.push_back(V);
 }
 
 // AddNodeID - Adds the Bit data of another ID to *this.
 void FoldingSetNodeID::AddNodeID(const FoldingSetNodeID &ID) {
   Bits.append(ID.Bits.begin(), ID.Bits.end());
 }
 
-/// ComputeHash - Compute a strong hash value for this FoldingSetNodeID, used to
-/// lookup the node in the FoldingSetBase.
-unsigned FoldingSetNodeID::ComputeHash() const {
-  return FoldingSetNodeIDRef(Bits.data(), Bits.size()).ComputeHash();
-}
-
 /// operator== - Used to compare two nodes to each other.
 ///
 bool FoldingSetNodeID::operator==(const FoldingSetNodeID &RHS) const {
   return *this == FoldingSetNodeIDRef(RHS.Bits.data(), RHS.Bits.size());
 }
 
 /// operator== - Used to compare two nodes to each other.
 ///