fcostaoliveira cb5d9cd9a4 Skip materializing the integer/fraction spans on the hot path ... parsed_number_string_t carries two span<UC const> members (integer, fraction) that are only read on the rare slow paths (digit_comp, and the >19-significant- digit truncation recompute). Materializing them on every parse forces the ~56/64- byte struct to be written out and marshaled through the by-value return, which shows up as backend/store pressure on the hot path. This adds a runtime `store_spans` flag (default true, so all existing callers are unchanged) to parse_number_string; from_chars_float_advanced parses with it false, attempts the Clinger and Eisel-Lemire fast paths inline, and only re-parses with spans on the two rare slow branches. The re-parse is pushed into a single `fastfloat_noinline` (noinline+cold) helper so the force-inlined hot scanner is emitted once rather than duplicated into the caller (without this the extra inline copies regress some targets, e.g. ARM gcc, by bloating the hot frame and lengthening the loop-carried dependency chain). A runtime flag is used deliberately rather than a template parameter: a template would create a second instantiation of the whole scanner whose icache cost wipes out the gain. Measured (per-parser microbench, median of 5, pinned core), fast_float from_chars <double>/<float>, vs the current tip: - Intel Ice Lake (Xeon 8360Y): +17-19% (gcc), Intel TMA shows backend-bound 26.0% -> 2.2% and retiring 60.3% -> 77.3% on short floats (the eliminated span spill), with -36% pipeline slots. - Intel Cascade Lake (Xeon 6248): +18-22% (gcc), +13-23% (clang). - ARM Neoverse-V2 (Graviton4): +73-196% (gcc), +8-11% (clang) -- the struct spill dominated the gcc hot loop there. Correctness: the full float exhaustive suite (exhaustive32, exhaustive32_64, exhaustive32_midpoint, random64) passes, and a 2^32 sweep is byte-identical to the current tip. Public from_chars / from_chars_advanced / parsed_number_string_t are unchanged.		2026-06-03 09:30:42 +01:00
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fast_float	Skip materializing the integer/fraction spans on the hot path	2026-06-03 09:30:42 +01:00