[llvm] [ADT] Use xxh3_64bits in DenseMapInfo<StringRef>::getHashValue (PR #191115)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay updated https://github.com/llvm/llvm-project/pull/191115

>From e31a89967a76eac1fa9e57c7df89eab0dc88e5c3 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Wed, 8 Apr 2026 22:49:19 -0700
Subject: [PATCH] [ADT] Use xxh3_64bits in
 DenseMapInfo<StringRef>::getHashValue

This function is heavily used in lld/ELF to hash symbol names. When
linking a clang Release+Asserts benchmark, this yields ~1% wall-time
improvement.

In LLVM_ENABLE_ABI_BREAKING_CHECKS builds, the result is XORed with
get_execution_seed() to preserve the non-deterministic seed protection
from Hashing.h.
---
 llvm/lib/Support/StringRef.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
index 2e8fba8cbfa37..8b303a2be0857 100644
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -13,6 +13,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/edit_distance.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/xxhash.h"
 #include <bitset>
 
 using namespace llvm;
@@ -614,5 +615,12 @@ unsigned DenseMapInfo<StringRef, void>::getHashValue(StringRef Val) {
          "Cannot hash the empty key!");
   assert(Val.data() != getTombstoneKey().data() &&
          "Cannot hash the tombstone key!");
-  return (unsigned)(hash_value(Val));
+  auto hash = xxh3_64bits(Val);
+  // In LLVM_ENABLE_ABI_BREAKING_CHECKS builds, the seed is non-deterministic
+  // per process (address of a function in LLVMSupport) to prevent having users
+  // depend on the particular hash values.
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+  hash ^= hashing::detail::get_execution_seed();
+#endif
+  return hash;
 }