On Thu, May 21, 2015 at 09:24:37AM -0600, Jeff Law wrote: > When combine needs to split a complex insn, it will canonicalize a > simple (mult X (const_int Y)) where Y is a power of 2 into the expected > (ashift X (const_int Y')) if the (mult ...) is selected as a split point. > > However if the split point is (plus (mult (X (const_int Y)) Z) combine > fails to canonicalize.
> OK for the trunk? Okay. Something went wrong with your changelog though. Rebasing changelogs is a recipe for disaster. The following is just copy-paste, but anyway... > + /* Similarly for (plus (mult FOO (const_int pow2))). */ > + if (split_code == PLUS > + && GET_CODE (XEXP (*split, 0)) == MULT > + && CONST_INT_P (XEXP (XEXP (*split, 0), 1)) > + && INTVAL (XEXP (XEXP (*split, 0), 1)) > 0 > + && (i = exact_log2 (UINTVAL (XEXP (XEXP (*split, 0), 1)))) >= 0) INTVAL (..) > 0 here disallows 1<<63 while exact_log2 allows it (with a 64-bit HWI). Most places don't check the > 0 and it doesn't seem necessary in the places that do. This won't ever trigger for a SImode 1<<31 either. None of this matters when we're just looking at scaled indexing, of course. But exact_log2 is much harder to use correctly than to use it incorrectly :-( Segher
