https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71802
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- if-conversion builds _51 = LOOP_VECTORIZED (3, 4); but new phi replacement stmt prephitmp_63 = prephitmp_62 != 0 ? _3 : prephitmp_62; Degenerate phi! prephitmp_52 = PHI <3(6)> Degenerate phi! prephitmp_54 = PHI <prephitmp_63(6)> Applying pattern match.pd:865, generic-match.c:429 Removing basic block 5 basic block 5, loop depth 1 pred: succ: Removing basic block 6 basic block 6, loop depth 1 pred: succ: Merging blocks 17 and 11 Merging blocks 4 and 24 Merging blocks 21 and 22 gimple_simplified to if (1 != 0) Applying pattern match.pd:853, gimple-match.c:164 Applying pattern match.pd:2618, gimple-match.c:57412 Removing basic block 23 basic block 23, loop depth 1 pred: 21 goto <bb 19>; succ: 19 fix_loop_structure: fixing up loops for function fix_loop_structure: removing loop 4 so there is no loop 4 in the end ... Before if-conversion the IL has <bb 11>: # prephitmp_52 = PHI <3(6)> # prephitmp_54 = PHI <prephitmp_63(6)> if (prephitmp_52 != 0) which likely messes things up. copyprop leaves us with this unpropagated constant by means of stmt folding during SSA substitution phase. We are generally not fixing up a LOOP_VECTORIZED call when loops vanish as we assume that doesn't happen between if-conversion and vectorization.
