[gcc r14-121] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011]

[gcc r14-121] tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR109011]

[Jakub Jelinek]

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).  */