Widen 16-bit object counts before absl::bit_width in CentralFreeList. - #719
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Widen 16-bit object counts before absl::bit_width in CentralFreeList.#719copybara-service[bot] wants to merge 1 commit into
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CentralFreeList::RemoveRange and ReleaseToSpans index the span-utilization histogram by absl::bit_width of the per-span allocated-object count, which is a uint16_t. The uint16_t overload of absl::bit_width dispatches to CountLeadingZeroes16, which emulates a 16-bit count-leading-zeros with extra shifts and masks on top of the native 32-bit clz/lzcnt instruction. Widen the count to uint32_t before calling absl::bit_width so codegen emits a single native clz/lzcnt; the resulting bit_width values and histogram bucket indices are unchanged. The rewrite is confined to the non-legacy locking path (TCMALLOC_INTERNAL_LEGACY_LOCKING), leaving the legacy path byte-for-byte identical. PiperOrigin-RevId: 979950772
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Widen 16-bit object counts before absl::bit_width in CentralFreeList.
CentralFreeList::RemoveRange and ReleaseToSpans index the span-utilization
histogram by absl::bit_width of the per-span allocated-object count, which is a
uint16_t. The uint16_t overload of absl::bit_width dispatches to
CountLeadingZeroes16, which emulates a 16-bit count-leading-zeros with extra
shifts and masks on top of the native 32-bit clz/lzcnt instruction. Widen the
count to uint32_t before calling absl::bit_width so codegen emits a single
native clz/lzcnt; the resulting bit_width values and histogram bucket indices
are unchanged.
The rewrite is confined to the non-legacy locking path
(TCMALLOC_INTERNAL_LEGACY_LOCKING), leaving the legacy path byte-for-byte
identical.