Second coverage batch, data-driven from the histogram. Diff harness validates
every op against the interpreter (MISMATCHES=0 over 47.96M blocks).
Update-form load/stores (24 ops: lbzu..stdux, lfsu..stfdux and their x-forms):
same access as the base form but with EA = gpr[ra] + offset (ra used directly —
update forms are illegal with ra==0) and rA := EA written back (zero-extended)
after the access. New ea_d_update/ea_x_update/write_ea_back helpers; loads write
rD then rA (so rA wins if rd==ra, matching the interpreter). stwu especially is
the standard stack-frame push in every function prologue.
mfspr/mtspr for LR and CTR only (64-bit field copies): the ubiquitous mflr/mtlr
prologue-epilogue pair and mtctr. covered() gates on the compile-time SPR number
so the offset always resolves; XER (packs CA/OV/SO) and the modelled SPRs stay
uncovered. This is the biggest single jump — mflr/mtlr gate almost every
non-leaf function's prologue and epilogue blocks.
Coverage (single-block, diff mode): 80.6% -> 82.8% (update forms) -> 89.6%
(mfspr/mtspr). 7/7 jit unit tests; foreground-validated per the bg-SIGTERM
finding. Carry-setting shifts (sraw*/srad*), rotate-double (rldic*), and XER
mfspr/mtspr remain for later batches; VMX128 is the long pole.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
5950dc86d5