-march=x86-64-v3 kept the port and the installer to CPUs with AVX2 and FMA. --cpu v2 compiles the generated code and the runtime for SSE4.2 instead. Without FMA3 the FP lowering calls fma/fmaf, so runtime/fma.c provides correctly rounded ones (musl, MIT) that honour MXCSR's rounding mode, FTZ and DAZ; the UCRT's software fallback rounds incorrectly by up to half an ulp. simd.h's fast paths keep their assumptions.
The installer's host check asks for x86-64-v2 and selects libtotkrt.a or libtotkrt-v2.a; both release scripts build and ship the pair. The differential tests compile fma.c as well, so a --cflags=-march=x86-64-v2 run tests it.
Tested on an i7-3770K (no AVX2, FMA or BMI) with an RTX 3060 Ti, game 1.4.3: the installer ran end to end, --selftest passed and play holds 40-60 fps at 1080p. fma and fmaf matched 152,288 exact vectors over two seeds, including ties, subnormals and every rounding mode, FTZ and DAZ combination. The v3 build is unchanged: fma.c is an empty translation unit there.
The FP helpers compared c->fpcr with a cached copy before every operation to resync MXCSR lazily. MXCSR now
follows FPCR.FZ at once: MSR FPCR calls rt_fpcr_sync, and so do rt_call (thread, fiber and host entry into guest
code), fiber resume (FIBER_FLAG_FLOAT_SWITCH fibers keep their own MXCSR) and the differential test harness per
case. op and vop only test FPCR.RMode for the slow path, and their redo check is one ordered-not-equal compare of
|r| with the smallest normal, the same NaN-or-smallest-normal set as before.
Hot guest code shrinks by about a quarter (132 functions holding half the guest cycles, 1.4.3); fight frame time
moves 1-3%, inside the run-to-run spread. lift, simd, func, atomic and flags_check pass on 1.4.3; simd.py fails
without the harness sync.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
CHEN Feng