https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117088
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Andrew Macleod from comment #4) ... > Its never been clear ot me why we still change loop branches to use !=. We > turn > for (int y = 0 ; y < 10; y++) > b[y] = x; > into > > if (y_1 != 10) > goto <bb 3>; [INV] > else > goto <bb 5>; [INV] > > and as a result, range analysis only picks up that y_1 is not 10. whereas > if that had remained > if (y_1 < 10) > goto <bb 3>; [INV] > else > goto <bb 5>; [INV] > > we'd at least have picked up y_1 is [-INF, 9] at in BB3 instead of > [-INF,9[11, +INF] > Instead, it has to depend on loop analysis to find values that could just be > apparent. It's probably a misguided optimization thinking that != is cheaper. It possibly is when it's != 0 as compared to < 0 for a decrement IV and the decrement is flag setting. IIRC we do this adjustment as part of VRP folding itself, right? I'd be fine dropping this (next stage1, that is).
