From the S76 func_80039B20 agent (79 ins, prior best 16 -> 10). Two findings.
A volatile-asm launder on the WRONG loop invariant displaced the address
chain and cost an entire cluster (16 -> 81 with it present); the matched
sibling func_8003A0E4 uses the plain idiom. Another invariant in the same
loop genuinely needs its launder. So the lever is per-invariant, not
per-loop, and it can go backwards.
Scope correction to Residual A (L875): the first-dying-operand / source-order
fix works on a SINGLE binary op and does NOT transfer to a PLUS chain —
measured byte-identical output when swapping operands on a 3-term chain,
because fold.c canonicalizes associative PLUS before combine sees it. Worth
recording as a negative result so nobody re-derives it.
Drew T
371a18b6de