Hi! On Thu, Oct 15, 2020 at 03:52:01PM +0800, guojiufu wrote: > I just had a check on below patch for PR66552. > https://gcc.gnu.org/pipermail/gcc-patches/2020-February/540930.html > It seems this patch works fine now. This patch fixes PR66552 which > request to optimizes (x shift (n mod C)) to > (x shift (n bit_and (C - 1))) when C is a constant and power of two.
> /* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR, > i.e. "X % C" into "X & (C - 1)", if X and C are positive. > Also optimize A % (C << N) where C is a power of 2, > - to A & ((C << N) - 1). */ > + to A & ((C << N) - 1). And optimize "A shift (B % C)" where C > + is a power of 2, shift operation included "<<" and ">>" and assume > + (B % C) will not be negative as shifts negative values would be UB, > + to "A shift (B & (C - 1))". */ Maybe this can be phrased better? Not that I have any proposed text :-/ The patch looks good to me, fwiw. Segher
