The pattern ends up using the argument more than one time which
isn't supported. When FFS directly maps to CTZ + 1 it works though.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
PR tree-optimization/123038
* tree-vect-patterns.cc (vect_recog_ctz_ffs_pattern): Reject
pattern for reductions when the call argument is used multiple
times.
* gcc.dg/vect/pr123038.c: New testcase.
---
gcc/testsuite/gcc.dg/vect/pr123038.c | 8 ++++++++
gcc/tree-vect-patterns.cc | 14 ++++++++++++++
2 files changed, 22 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/vect/pr123038.c
diff --git a/gcc/testsuite/gcc.dg/vect/pr123038.c
b/gcc/testsuite/gcc.dg/vect/pr123038.c
new file mode 100644
index 00000000000..bca831f9c08
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr123038.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+
+unsigned char f(int b)
+{
+ for (int a = 0; a < 10; a += 1)
+ b = __builtin_ffs(b);
+ return b;
+}
diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 555986b4fec..af64cb84e41 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -1914,6 +1914,9 @@ vect_recog_ctz_ffs_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
&& val_new == prec)
|| (ifnnew == IFN_POPCOUNT && ifn == IFN_CTZ))
{
+ if (vect_is_reduction (stmt_vinfo))
+ return NULL;
+
/* .CTZ (X) = PREC - .CLZ ((X - 1) & ~X)
.CTZ (X) = .POPCOUNT ((X - 1) & ~X). */
if (ifnnew == IFN_CLZ)
@@ -1952,6 +1955,9 @@ vect_recog_ctz_ffs_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
}
else if (ifnnew == IFN_CLZ)
{
+ if (vect_is_reduction (stmt_vinfo))
+ return NULL;
+
/* .CTZ (X) = (PREC - 1) - .CLZ (X & -X)
.FFS (X) = PREC - .CLZ (X & -X). */
sub = prec - (ifn == IFN_CTZ);
@@ -1971,6 +1977,9 @@ vect_recog_ctz_ffs_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
}
else if (ifnnew == IFN_POPCOUNT)
{
+ if (vect_is_reduction (stmt_vinfo))
+ return NULL;
+
/* .CTZ (X) = PREC - .POPCOUNT (X | -X)
.FFS (X) = (PREC + 1) - .POPCOUNT (X | -X). */
sub = prec + (ifn == IFN_FFS);
@@ -1993,6 +2002,11 @@ vect_recog_ctz_ffs_pattern (vec_info *vinfo,
stmt_vec_info stmt_vinfo,
/* .FFS (X) = .CTZ (X) + 1. */
add = 1;
val_cmp++;
+
+ if (vect_is_reduction (stmt_vinfo)
+ && defined_at_zero
+ && (!defined_at_zero_new || val != val_cmp))
+ return NULL;
}
/* Create B = .IFNNEW (A). */
--
2.51.0
