From 87c9bae4e32b54829dce0a93ff735412d5f684f8 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 20 Apr 2023 19:44:27 +0200
Subject: [PATCH] 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).
---
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 d1b86e8b5e00..a49b09539776 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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