From e1318b1d03725bda7bf8c9f76959007e2f6067d8 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <nnethercote@mozilla.com>
Date: Mon, 16 Apr 2018 08:37:15 +1000
Subject: [PATCH] Bug 1451278 - Remove ConstExpr hash functions. r=froydnj

MozReview-Commit-ID: L6yRyt4DZRR

--HG--
extra : rebase_source : 2d56a50b1a99e66c397165b9b851e23ca66d97a0
---
 mfbt/HashFunctions.h | 33 ++++-----------------------------
 xpcom/ds/nsAtom.h    |  2 +-
 2 files changed, 5 insertions(+), 30 deletions(-)

diff --git a/mfbt/HashFunctions.h b/mfbt/HashFunctions.h
index 737e322844e0..ad7b708ceef7 100644
--- a/mfbt/HashFunctions.h
+++ b/mfbt/HashFunctions.h
@@ -210,29 +210,16 @@ HashGeneric(Args... aArgs)
 namespace detail {
 
 template<typename T>
-uint32_t
+constexpr uint32_t
 HashUntilZero(const T* aStr)
 {
   uint32_t hash = 0;
-  for (T c; (c = *aStr); aStr++) {
+  for (; T c = *aStr; aStr++) {
     hash = AddToHash(hash, c);
   }
   return hash;
 }
 
-// This is a `constexpr` alternative to HashUntilZero(const T*). It should
-// only be used for compile-time computation because it uses recursion.
-// XXX: once support for GCC 4.9 is dropped, this function should be removed
-// and HashUntilZero(const T*) should be made `constexpr`.
-template<typename T>
-constexpr uint32_t
-ConstExprHashUntilZero(const T* aStr, uint32_t aHash)
-{
-  return !*aStr
-       ? aHash
-       : ConstExprHashUntilZero(aStr + 1, AddToHash(aHash, *aStr));
-}
-
 template<typename T>
 uint32_t
 HashKnownLength(const T* aStr, size_t aLength)
@@ -271,25 +258,13 @@ HashString(const unsigned char* aStr, size_t aLength)
   return detail::HashKnownLength(aStr, aLength);
 }
 
-MOZ_MUST_USE inline uint32_t
-HashString(const char16_t* aStr)
-{
-  return detail::HashUntilZero(aStr);
-}
-
-// This is a `constexpr` alternative to HashString(const char16_t*). It should
-// only be used for compile-time computation because it uses recursion.
-//
 // You may need to use the
 // MOZ_{PUSH,POP}_DISABLE_INTEGRAL_CONSTANT_OVERFLOW_WARNING macros if you use
 // this function. See the comment on those macros' definitions for more detail.
-//
-// XXX: once support for GCC 4.9 is dropped, this function should be removed
-// and HashString(const char16_t*) should be made `constexpr`.
 MOZ_MUST_USE constexpr uint32_t
-ConstExprHashString(const char16_t* aStr)
+HashString(const char16_t* aStr)
 {
-  return detail::ConstExprHashUntilZero(aStr, 0);
+  return detail::HashUntilZero(aStr);
 }
 
 MOZ_MUST_USE inline uint32_t
diff --git a/xpcom/ds/nsAtom.h b/xpcom/ds/nsAtom.h
index 7fb9f4fe97b1..b4999e5f9f7e 100644
--- a/xpcom/ds/nsAtom.h
+++ b/xpcom/ds/nsAtom.h
@@ -107,7 +107,7 @@ protected:
   constexpr nsAtom(const char16_t* aStr, uint32_t aLength)
     : mLength(aLength)
     , mKind(static_cast<uint32_t>(nsAtom::AtomKind::Static))
-    , mHash(mozilla::ConstExprHashString(aStr))
+    , mHash(mozilla::HashString(aStr))
   {}
 
   // Used by nsDynamicAtom.