Worker F's 0x8002622C (44 B) — A RECORDED NEGATIVE OVERTURNED, with a new class.
The old record said 'cc1 folds it, unreachable' and tried FOUR ALGEBRAIC re-spellings. All four
were doomed: the fold is at RTL combine, not in the front end, so no re-spelling can avoid it.
Only LIVENESS can. Same body with 'return 0' is 32 B LENGTH-MISMATCH; with 'return n' (the
difference live past the addition) it is 44/0/MATCH. Diagnostic that proves the pass: cc1 -da
shows the minus present in the .flow dump and gone in the .combine dump, while cse/cse2/jump/
loop/sched/sched2 all still contain it.
181: when an original keeps an arithmetically-cancelling pair (subu+addu, x-c+c), the intermediate
is LIVE PAST the second operation — find the later reader.
182: a negative with a NAMED mechanism is overturnable; one without is not. 'cc1 folds it' is not
a classification; 'RTL combine cancels it, and algebraic re-spelling cannot reach combine' is,
and it immediately implies the liveness lever.
Christopher Williams
b0ed17d494