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From: Jakub Jelinek <jakub@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-121] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011] Date: Thu, 20 Apr 2023 17:45:42 +0000 (GMT) [thread overview] Message-ID: <20230420174542.4B9093858422@sourceware.org> (raw) https://gcc.gnu.org/g:87c9bae4e32b54829dce0a93ff735412d5f684f8 commit r14-121-g87c9bae4e32b54829dce0a93ff735412d5f684f8 Author: Jakub Jelinek <jakub@redhat.com> Date: Thu Apr 20 19:44:27 2023 +0200 tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011] 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. 2023-04-20 Jakub Jelinek <jakub@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). Diff: --- gcc/tree-vect-patterns.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc index d1b86e8b5e0..a49b0953977 100644 --- a/gcc/tree-vect-patterns.cc +++ b/gcc/tree-vect-patterns.cc @@ -1630,7 +1630,7 @@ vect_recog_ctz_ffs_pattern (vec_info *vinfo, stmt_vec_info stmt_vinfo, && 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). */
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