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Bug 1967062 - Partial Backout of "Bug 933149 - Remove PodCopy loop heuristic r=mstange" on Linux only. a=dmeehan

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We'll remove the loop heuristic on non-linux platforms, but keep it there as
that's where it continues to be effective.

Differential Revision: https://phabricator.services.mozilla.com/D250470
This commit is contained in:
Matthew Gaudet
2025-06-04 17:38:05 +00:00
committed by dmeehan@mozilla.com
parent c00915984c
commit f5f4c2a04d
2 changed files with 19 additions and 0 deletions
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6
js/src/builtin/String.cpp
View File

@@ -8,6 +8,7 @@
#include "mozilla/Attributes.h" #include "mozilla/Attributes.h"
#include "mozilla/CheckedInt.h" #include "mozilla/CheckedInt.h"
#include "mozilla/Compiler.h"
#include "mozilla/FloatingPoint.h" #include "mozilla/FloatingPoint.h"
#if JS_HAS_INTL_API #if JS_HAS_INTL_API
# include "mozilla/intl/String.h" # include "mozilla/intl/String.h"
@@ -544,7 +545,12 @@ template <typename DestChar, typename SrcChar>
static inline void CopyChars(DestChar* destChars, const SrcChar* srcChars, static inline void CopyChars(DestChar* destChars, const SrcChar* srcChars,
size_t length) { size_t length) {
if constexpr (std::is_same_v<DestChar, SrcChar>) { if constexpr (std::is_same_v<DestChar, SrcChar>) {
#if MOZ_IS_GCC
// Directly call memcpy to work around bug 1863131.
memcpy(destChars, srcChars, length * sizeof(DestChar));
#else
PodCopy(destChars, srcChars, length); PodCopy(destChars, srcChars, length);
#endif
} else { } else {
for (size_t i = 0; i < length; i++) { for (size_t i = 0; i < length; i++) {
destChars[i] = srcChars[i]; destChars[i] = srcChars[i];

13
mfbt/PodOperations.h
View File

@@ -96,6 +96,19 @@ static MOZ_ALWAYS_INLINE void PodCopy(T* aDst, const T* aSrc, size_t aNElem) {
MOZ_ASSERT(aDst + aNElem <= aSrc || aSrc + aNElem <= aDst, MOZ_ASSERT(aDst + aNElem <= aSrc || aSrc + aNElem <= aDst,
"destination and source must not overlap"); "destination and source must not overlap");
// Linux memcpy for small sizes seems slower than on other
// platforms. So we use a loop for small sizes there only.
//
// See Bug 1967062 for details.
#if defined(XP_LINUX)
if (aNElem < 128) {
for (const T* srcend = aSrc + aNElem; aSrc < srcend; aSrc++, aDst++) {
*aDst = *aSrc;
}
return;
}
#endif
memcpy(aDst, aSrc, aNElem * sizeof(T)); memcpy(aDst, aSrc, aNElem * sizeof(T));
} }