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Don't use PodCopy/PodMove to implement typed-array element-to-element copying

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Standard std::copy and std::copy_n are readily optimized to the same thing, and they don't have a non-obvious requirement that the type being copied be trivial.
This commit is contained in:
trav90 2018-09-19 19:05:22 -05:00 • committed by Roy Tam
commit 74983ef77e
1 changed files with 17 additions and 4 deletions
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21
js/src/vm/TypedArrayCommon.h
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@ -11,7 +11,8 @@
#include "mozilla/Assertions.h" #include "mozilla/Assertions.h"
#include "mozilla/FloatingPoint.h" #include "mozilla/FloatingPoint.h"
#include "mozilla/PodOperations.h"
#include <algorithm>
#include "jsarray.h" #include "jsarray.h"
#include "jscntxt.h" #include "jscntxt.h"
@ -245,12 +246,24 @@ class UnsharedOps
template<typename T> template<typename T>
static void podCopy(SharedMem<T*> dest, SharedMem<T*> src, size_t nelem) { static void podCopy(SharedMem<T*> dest, SharedMem<T*> src, size_t nelem) {
mozilla::PodCopy(dest.unwrapUnshared(), src.unwrapUnshared(), nelem); // std::copy_n better matches the argument values/types of this
// function, but as noted below it allows the input/output ranges to
// overlap. std::copy does not, so use it so the compiler has extra
// ability to optimize.
const auto* first = src.unwrapUnshared();
const auto* last = first + nelem;
auto* result = dest.unwrapUnshared();
std::copy(first, last, result);
} }
template<typename T> template<typename T>
static void podMove(SharedMem<T*> dest, SharedMem<T*> src, size_t nelem) { static void podMove(SharedMem<T*> dest, SharedMem<T*> src, size_t n) {
mozilla::PodMove(dest.unwrapUnshared(), src.unwrapUnshared(), nelem); // std::copy_n copies from |src| to |dest| starting from |src|, so
// input/output ranges *may* permissibly overlap, as this function
// allows.
const auto* start = src.unwrapUnshared();
auto* result = dest.unwrapUnshared();
std::copy_n(start, n, result);
} }
static SharedMem<void*> extract(TypedArrayObject* obj) { static SharedMem<void*> extract(TypedArrayObject* obj) {