From 93c2d559a12bf72c7eb96b6a2a5a5bb77ecdc4b4 Mon Sep 17 00:00:00 2001
From: Ben Clayton <bclayton@google.com>
Date: Tue, 23 Aug 2022 19:09:34 +0000
Subject: [PATCH] tint/utils: Default to using Hasher instead of std::hash

STL std::hash<T*> implementations have a tendency of just reinterpreting the
pointer as a size_t. This is fast, but produces a bad hash, as most pointers
tend to be 4 or 16 byte aligned. The lack of entropy in the LSBs causes
clustering of hashmap slots. Use tint::utils::Hasher to get better hashes.

Change-Id: Ife768d573cd1875e746ca9d77a4ac19e43b06aca
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/99281
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
---
 src/tint/utils/hashmap.h | 3 ++-
 src/tint/utils/hashset.h | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/tint/utils/hashmap.h b/src/tint/utils/hashmap.h
index 81bebf2410..e17938987f 100644
--- a/src/tint/utils/hashmap.h
+++ b/src/tint/utils/hashmap.h
@@ -19,6 +19,7 @@
 #include <optional>
 #include <utility>
 
+#include "src/tint/utils/hash.h"
 #include "src/tint/utils/hashset.h"
 
 namespace tint::utils {
@@ -31,7 +32,7 @@ namespace tint::utils {
 template <typename K,
           typename V,
           size_t N,
-          typename HASH = std::hash<K>,
+          typename HASH = Hasher<K>,
           typename EQUAL = std::equal_to<K>>
 class Hashmap {
     /// LazyCreator is a transient structure used to late-build the Entry::value, when inserted into
diff --git a/src/tint/utils/hashset.h b/src/tint/utils/hashset.h
index f88a304bf9..3009c72eba 100644
--- a/src/tint/utils/hashset.h
+++ b/src/tint/utils/hashset.h
@@ -23,6 +23,7 @@
 #include <utility>
 
 #include "src/tint/debug.h"
+#include "src/tint/utils/hash.h"
 #include "src/tint/utils/vector.h"
 
 namespace tint::utils {
@@ -39,7 +40,7 @@ enum class AddAction {
 
 /// An unordered set that uses a robin-hood hashing algorithm.
 /// @see the fantastic tutorial: https://programming.guide/robin-hood-hashing.html
-template <typename T, size_t N, typename HASH = std::hash<T>, typename EQUAL = std::equal_to<T>>
+template <typename T, size_t N, typename HASH = Hasher<T>, typename EQUAL = std::equal_to<T>>
 class Hashset {
     /// A slot is a single entry in the underlying vector.
     /// A slot can either be empty or filled with a value. If the slot is empty, #hash and #distance