https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89247
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> --- I think this is a duplicate of that other bug, at least I seem to remember seeing this: <bb 16> [local count: 536817226]: # prephitmp_12 = PHI <1(15)> if (prephitmp_12 != 0) goto <bb 10>; [50.00%] else goto <bb 17>; [50.00%] when we if-convert this CFG cleanup elides the loop. It is ch_vect that leaves us with this PHI when it operates on <bb 2> [local count: 53687]: a.0_1 = a; pretmp_4 = *a.0_1; <bb 3> [local count: 536870913]: # prephitmp_5 = PHI <1(5), pretmp_4(2)> d: if (prephitmp_5 != 0) goto <bb 10>; [50.00%] else goto <bb 5>; [50.00%] <bb 5> [local count: 536870913]: *a.0_1 = 1; goto <bb 3>; [100.00%] on trunk we run CSE on the copied blocks but not the resulting loop body. If we CSE also the loop body the PR is fixed but the expense is possibly too large? Another possibility is to somehow link .LOOP_VECTORIZED from loop info and elide that when a loop is removed (which is what happens here). Or simply do that in if-conversion.
