From e74a63076b7c21bd45f5156fc028d41db8aa5eb0 Mon Sep 17 00:00:00 2001
From: Alon Zakai <azakai@google.com>
Date: Wed, 28 Sep 2022 16:01:58 -0700
Subject: [GUFA] Improve hashing (#5091)

Avoid manually doing bitshifts etc. - leave combining to the core hash
logic, which can do a better job.
---
 src/ir/possible-contents.h | 21 ++++++++++-----------
 src/support/hash.h         |  2 +-
 2 files changed, 11 insertions(+), 12 deletions(-)

(limited to 'src')

diff --git a/src/ir/possible-contents.h b/src/ir/possible-contents.h
index f7c39e1f9..863a0dbab 100644
--- a/src/ir/possible-contents.h
+++ b/src/ir/possible-contents.h
@@ -21,6 +21,7 @@
 
 #include "ir/possible-constant.h"
 #include "ir/subtypes.h"
+#include "support/hash.h"
 #include "support/small_vector.h"
 #include "wasm-builder.h"
 #include "wasm.h"
@@ -213,23 +214,21 @@ public:
   }
 
   size_t hash() const {
-    // Encode this using three bits for the variant type, then the rest of the
-    // contents.
-    if (isNone()) {
-      return 0;
+    // First hash the index of the variant, then add the internals for each.
+    size_t ret = std::hash<size_t>()(value.index());
+    if (isNone() || isMany()) {
+      // Nothing to add.
     } else if (isLiteral()) {
-      return size_t(1) | (std::hash<Literal>()(getLiteral()) << 3);
+      rehash(ret, getLiteral());
     } else if (isGlobal()) {
-      return size_t(2) | (std::hash<Name>()(getGlobal()) << 3);
+      rehash(ret, getGlobal());
     } else if (auto* coneType = std::get_if<ConeType>(&value)) {
-      return size_t(3) | ((std::hash<std::pair<Type, Index>>{}(
-                            {coneType->type, coneType->depth}))
-                          << 3);
-    } else if (isMany()) {
-      return 4;
+      rehash(ret, coneType->type);
+      rehash(ret, coneType->depth);
     } else {
       WASM_UNREACHABLE("bad variant");
     }
+    return ret;
   }
 
   void dump(std::ostream& o, Module* wasm = nullptr) const {
diff --git a/src/support/hash.h b/src/support/hash.h
index d3a858698..fb0e710a5 100644
--- a/src/support/hash.h
+++ b/src/support/hash.h
@@ -29,7 +29,7 @@ template<typename T> inline std::size_t hash(const T& value) {
 
 // Combines two digests into the first digest. Use instead of `rehash` if
 // `otherDigest` is another digest and not a `size_t` value.
-static inline void hash_combine(std::size_t& digest, std::size_t otherDigest) {
+inline void hash_combine(std::size_t& digest, const std::size_t otherDigest) {
   // see: boost/container_hash/hash.hpp
   // The constant is the N-bits reciprocal of the golden ratio:
   //  phi = (1 + sqrt(5)) / 2
-- 
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