[Lex] Replace hash_combine with a stable hash

Author: MaskRay

clang/lib/Lex/HeaderSearch.cpp

@@ -25,18 +25,19 @@
 #include "clang/Lex/Preprocessor.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/VirtualFileSystem.h"
+#include "llvm/Support/xxhash.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
@@ -282,10 +283,10 @@ std::string HeaderSearch::getCachedModuleFileNameImpl(StringRef ModuleName,
     if (getModuleMap().canonicalizeModuleMapPath(CanonicalPath))
       return {};
 
-    llvm::hash_code Hash = llvm::hash_combine(CanonicalPath.str().lower());
+    auto Hash = llvm::xxh3_64bits(CanonicalPath.str().lower());
 
     SmallString<128> HashStr;
-    llvm::APInt(64, size_t(Hash)).toStringUnsigned(HashStr, /*Radix*/36);
+    llvm::APInt(64, Hash).toStringUnsigned(HashStr, /*Radix*/36);
     llvm::sys::path::append(Result, ModuleName + "-" + HashStr + ".pcm");
   }
   return Result.str().str();