Hi! I've noticed I've made a typo, ifn in this function this late is always only IFN_CTZ or IFN_FFS, never IFN_CLZ.
Due to this typo, we weren't using the originally intended .CTZ (X) = .POPCOUNT ((X - 1) & ~X) but .CTZ (X) = PREC - .POPCOUNT (X | -X) instead when we want to emit __builtin_ctz*/.CTZ using .POPCOUNT. Both compute the same value, both are defined at 0 with the same value (PREC), both have same number of GIMPLE statements, but I think the former ought to be preferred, because lots of targets have andn as a single operation rather than two, and also putting a -1 constant into a vector register is often cheaper than vector with broadcast PREC power of two value. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2023-04-20 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/109011 * tree-vect-patterns.cc (vect_recog_ctz_ffs_pattern): Use .CTZ (X) = .POPCOUNT ((X - 1) & ~X) in preference to .CTZ (X) = PREC - .POPCOUNT (X | -X). --- gcc/tree-vect-patterns.cc.jj 2023-04-20 11:55:03.576154120 +0200 +++ gcc/tree-vect-patterns.cc 2023-04-20 12:09:17.884633795 +0200 @@ -1630,7 +1630,7 @@ vect_recog_ctz_ffs_pattern (vec_info *vi && defined_at_zero_new && val == prec && val_new == prec) - || (ifnnew == IFN_POPCOUNT && ifn == IFN_CLZ)) + || (ifnnew == IFN_POPCOUNT && ifn == IFN_CTZ)) { /* .CTZ (X) = PREC - .CLZ ((X - 1) & ~X) .CTZ (X) = .POPCOUNT ((X - 1) & ~X). */ Jakub