https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712
--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Marc Glisse from comment #11) > (In reply to Jakub Jelinek from comment #10) > > I know, it will be a small complication, sure, but it can be handled. > > Ah, I think I understand now. But still > > x=-1 > a=INT_MAX > a*x+x gives INT_MIN without overflow. > Now a could be (int)((unsigned)b-1) where b is INT_MIN. But we don't want to > generate b*x for that (INT_MIN*-1), since it overflows. So we would need to > do the multiplication in some unsigned type. If we go there (do everything > unsigned), we could do the transformation always, and restricting it is just > a heuristic for when the signed type information might be more useful than > the factorized form. The comments at least in fold-const.c say clearly that we do not want to perform unsigned multiplication. I was talking about the int a, b; ((int)(a-1U))*b+b transformation into a*b. Even for a=0, it is -1*b+b into 0, there could be UB before, but there is none after. a=INT_MIN used to be INT_MAX*b+b and newly INT_MIN*b, well defined for b=0, UB for b > 0, UB for b < -1, but it is true that INT_MAX*-1+-1 is well defined INT_MIN, but INT_MIN*-1 is UB. So guess we need to use range info only then.
