remove compare and branch in fast path for c++ operator delete[]
Summary: sdallocx is checking a flag that will never be set (at least in the provided C++ destructor implementation). This branch will probably only rarely be mispredicted however it removes two instructions in sdallocx and one at the callsite (to zero out flags).
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@ -2909,6 +2909,7 @@ sub RemoveUninterestingFrames {
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'@JEMALLOC_PREFIX@xallocx',
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'@JEMALLOC_PREFIX@dallocx',
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'@JEMALLOC_PREFIX@sdallocx',
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'@JEMALLOC_PREFIX@sdallocx_noflags',
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'tc_calloc',
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'tc_cfree',
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'tc_malloc',
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@ -51,5 +51,6 @@ void jemalloc_prefork(void);
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void jemalloc_postfork_parent(void);
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void jemalloc_postfork_child(void);
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bool malloc_initialized(void);
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void je_sdallocx_noflags(void *ptr, size_t size);
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#endif /* JEMALLOC_INTERNAL_EXTERNS_H */
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@ -3522,6 +3522,18 @@ je_sdallocx(void *ptr, size_t size, int flags) {
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LOG("core.sdallocx.exit", "");
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}
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void JEMALLOC_NOTHROW
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je_sdallocx_noflags(void *ptr, size_t size) {
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LOG("core.sdallocx.entry", "ptr: %p, size: %zu, flags: 0", ptr,
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size);
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if (!free_fastpath(ptr, size, true)) {
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sdallocx_default(ptr, size, 0);
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}
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LOG("core.sdallocx.exit", "");
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}
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JEMALLOC_EXPORT size_t JEMALLOC_NOTHROW
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JEMALLOC_ATTR(pure)
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je_nallocx(size_t size, int flags) {
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@ -128,14 +128,14 @@ operator delete(void *ptr, std::size_t size) noexcept {
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if (unlikely(ptr == nullptr)) {
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return;
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}
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je_sdallocx(ptr, size, /*flags=*/0);
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je_sdallocx_noflags(ptr, size);
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}
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void operator delete[](void *ptr, std::size_t size) noexcept {
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if (unlikely(ptr == nullptr)) {
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return;
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}
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je_sdallocx(ptr, size, /*flags=*/0);
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je_sdallocx_noflags(ptr, size);
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}
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#endif // __cpp_sized_deallocation
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