From 6e1293b5f7142552f87c3ad84efa7de64dbea418 Mon Sep 17 00:00:00 2001
From: Mike Hommey <mh+mozilla@glandium.org>
Date: Tue, 9 Jan 2024 01:48:31 +0000
Subject: [PATCH] Bug 1718516 - Fix AddToHash of 64-bits numbers on 32-bits
 platforms. r=nika,anba

Differential Revision: https://phabricator.services.mozilla.com/D197302
---
 js/src/jit/MacroAssembler.cpp | 15 +--------------
 mfbt/HashFunctions.h          | 25 ++++++++++++++-----------
 2 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/js/src/jit/MacroAssembler.cpp b/js/src/jit/MacroAssembler.cpp
index a62ea0f61395..d6f7de6c358b 100644
--- a/js/src/jit/MacroAssembler.cpp
+++ b/js/src/jit/MacroAssembler.cpp
@@ -7639,18 +7639,7 @@ void MacroAssembler::prepareHashNonGCThing(ValueOperand value, Register result,
   move64(value.toRegister64(), r64);
   rshift64Arithmetic(Imm32(32), r64);
 #else
-  // TODO: This seems like a bug in mozilla::detail::AddUintptrToHash().
-  // The uint64_t input is first converted to uintptr_t and then back to
-  // uint64_t. But |uint64_t(uintptr_t(bits))| actually only clears the high
-  // bits, so this computation:
-  //
-  // aValue = uintptr_t(bits)
-  // v2 = static_cast<uint32_t>(static_cast<uint64_t>(aValue) >> 32)
-  //
-  // really just sets |v2 = 0|. And that means the xor-operation in AddU32ToHash
-  // can be optimized away, because |x ^ 0 = x|.
-  //
-  // Filed as bug 1718516.
+  move32(value.typeReg(), temp);
 #endif
 
   // mozilla::WrappingMultiply(kGoldenRatioU32, RotateLeft5(aHash) ^ aValue);
@@ -7660,9 +7649,7 @@ void MacroAssembler::prepareHashNonGCThing(ValueOperand value, Register result,
   // mozilla::WrappingMultiply(kGoldenRatioU32, RotateLeft5(aHash) ^ aValue);
   // with |aHash = <above hash>| and |aValue = v2|.
   rotateLeft(Imm32(5), result, result);
-#ifdef JS_PUNBOX64
   xor32(temp, result);
-#endif
 
   // Combine |mul32| and |scrambleHashCode| by directly multiplying with
   // |kGoldenRatioU32 * kGoldenRatioU32|.
diff --git a/mfbt/HashFunctions.h b/mfbt/HashFunctions.h
index 4b740a3db16b..b9c2d5e98d7a 100644
--- a/mfbt/HashFunctions.h
+++ b/mfbt/HashFunctions.h
@@ -153,17 +153,20 @@ constexpr HashNumber AddU32ToHash(HashNumber aHash, uint32_t aValue) {
 }
 
 /**
- * AddUintptrToHash takes sizeof(uintptr_t) as a template parameter.
+ * AddUintNToHash takes sizeof(int_type) as a template parameter.
+ * Changes to these functions need to be propagated to
+ * MacroAssembler::prepareHashNonGCThing, which inlines them manually for
+ * the JIT.
  */
-template <size_t PtrSize>
-constexpr HashNumber AddUintptrToHash(HashNumber aHash, uintptr_t aValue) {
+template <size_t Size>
+constexpr HashNumber AddUintNToHash(HashNumber aHash, uint64_t aValue) {
   return AddU32ToHash(aHash, static_cast<uint32_t>(aValue));
 }
 
 template <>
-inline HashNumber AddUintptrToHash<8>(HashNumber aHash, uintptr_t aValue) {
+inline HashNumber AddUintNToHash<8>(HashNumber aHash, uint64_t aValue) {
   uint32_t v1 = static_cast<uint32_t>(aValue);
-  uint32_t v2 = static_cast<uint32_t>(static_cast<uint64_t>(aValue) >> 32);
+  uint32_t v2 = static_cast<uint32_t>(aValue >> 32);
   return AddU32ToHash(AddU32ToHash(aHash, v1), v2);
 }
 
@@ -196,23 +199,23 @@ template <typename A>
 
   static_assert(sizeof(aA) == sizeof(uintptr_t), "Strange pointer!");
 
-  return detail::AddUintptrToHash<sizeof(uintptr_t)>(aHash, uintptr_t(aA));
+  return detail::AddUintNToHash<sizeof(uintptr_t)>(aHash, uintptr_t(aA));
 }
 
-// We use AddUintptrToHash() for hashing all integral types.  8-byte integral
+// We use AddUintNToHash() for hashing all integral types.  8-byte integral
 // types are treated the same as 64-bit pointers, and smaller integral types are
-// first implicitly converted to 32 bits and then passed to AddUintptrToHash()
+// first implicitly converted to 32 bits and then passed to AddUintNToHash()
 // to be hashed.
 template <typename T, std::enable_if_t<std::is_integral_v<T>, int> = 0>
 [[nodiscard]] constexpr HashNumber AddToHash(HashNumber aHash, T aA) {
-  return detail::AddUintptrToHash<sizeof(T)>(aHash, aA);
+  return detail::AddUintNToHash<sizeof(T)>(aHash, aA);
 }
 
 template <typename T, std::enable_if_t<std::is_enum_v<T>, int> = 0>
 [[nodiscard]] constexpr HashNumber AddToHash(HashNumber aHash, T aA) {
-  // Hash using AddUintptrToHash with the underlying type of the enum type
+  // Hash using AddUintNToHash with the underlying type of the enum type
   using UnderlyingType = typename std::underlying_type<T>::type;
-  return detail::AddUintptrToHash<sizeof(UnderlyingType)>(
+  return detail::AddUintNToHash<sizeof(UnderlyingType)>(
       aHash, static_cast<UnderlyingType>(aA));
 }