https://gcc.gnu.org/g:5aca8510abea6c3fac3336a7445863db07fd4a06
commit r16-1673-g5aca8510abea6c3fac3336a7445863db07fd4a06
Author: Richard Biener <rguent...@suse.de>
Date: Wed Jun 25 10:36:59 2025 +0200
tree-optimization/109892 - SLP reduction of fma
The following adds the ability to vectorize a fma reduction pair
as SLP reduction (we cannot yet handle ternary association in
reduction vectorization yet).
PR tree-optimization/109892
* tree-vect-loop.cc (check_reduction_path): Handle fma.
(vectorizable_reduction): Apply FOLD_LEFT_REDUCTION code
generation constraints.
* gcc.dg/vect/vect-reduc-fma-1.c: New testcase.
* gcc.dg/vect/vect-reduc-fma-2.c: Likewise.
* gcc.dg/vect/vect-reduc-fma-3.c: Likewise.
Diff:
---
gcc/testsuite/gcc.dg/vect/vect-reduc-fma-1.c | 15 +++++++++++++++
gcc/testsuite/gcc.dg/vect/vect-reduc-fma-2.c | 20 ++++++++++++++++++++
gcc/testsuite/gcc.dg/vect/vect-reduc-fma-3.c | 16 ++++++++++++++++
gcc/tree-vect-loop.cc | 17 +++++++++++++++++
4 files changed, 68 insertions(+)
diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-1.c
b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-1.c
new file mode 100644
index 000000000000..e958b43e23b6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-mfma" { target { x86_64-*-* i?86-*-* } } } */
+
+double f(double x[], long n)
+{
+ double r0 = 0, r1 = 0;
+ for (; n; x += 2, n--) {
+ r0 = __builtin_fma(x[0], x[0], r0);
+ r1 = __builtin_fma(x[1], x[1], r1);
+ }
+ return r0 + r1;
+}
+
+/* We should vectorize this as SLP reduction. */
+/* { dg-final { scan-tree-dump "loop vectorized using 16 byte vectors and
unroll factor 1" "vect" { target { x86_64-*-* i?86-*-* } } } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-2.c
b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-2.c
new file mode 100644
index 000000000000..ea1ca9720e5a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-2.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-ffp-contract=on" } */
+/* { dg-additional-options "-mfma" { target { x86_64-*-* i?86-*-* } } } */
+
+static double muladd(double x, double y, double z)
+{
+ return x * y + z;
+}
+double g(double x[], long n)
+{
+ double r0 = 0, r1 = 0;
+ for (; n; x += 2, n--) {
+ r0 = muladd(x[0], x[0], r0);
+ r1 = muladd(x[1], x[1], r1);
+ }
+ return r0 + r1;
+}
+
+/* We should vectorize this as SLP reduction. */
+/* { dg-final { scan-tree-dump "loop vectorized using 16 byte vectors and
unroll factor 1" "vect" { target { x86_64-*-* i?86-*-* } } } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-3.c
b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-3.c
new file mode 100644
index 000000000000..10cecedd8e5f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-fma-3.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-ffast-math" } */
+/* { dg-additional-options "-mfma" { target { x86_64-*-* i?86-*-* } } } */
+
+double f(double x[], long n)
+{
+ double r0 = 0, r1 = 0;
+ for (; n; x += 2, n--) {
+ r0 = __builtin_fma(x[0], x[0], r0);
+ r1 = __builtin_fma(x[1], x[1], r1);
+ }
+ return r0 + r1;
+}
+
+/* We should vectorize this as SLP reduction, higher VF possible. */
+/* { dg-final { scan-tree-dump "optimized: loop vectorized" "vect" { target {
x86_64-*-* i?86-*-* } } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 9ee8e50ee75a..5b6769af31c3 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -4126,6 +4126,10 @@ pop:
if (op.ops[2] == op.ops[opi])
neg = ! neg;
}
+ /* For an FMA the reduction code is the PLUS if the addition chain
+ is the reduction. */
+ else if (op.code == IFN_FMA && opi == 2)
+ op.code = PLUS_EXPR;
if (CONVERT_EXPR_CODE_P (op.code)
&& tree_nop_conversion_p (op.type, TREE_TYPE (op.ops[0])))
;
@@ -8070,6 +8074,19 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
"in-order reduction chain without SLP.\n");
return false;
}
+ /* Code generation doesn't support function calls other
+ than .COND_*. */
+ if (!op.code.is_tree_code ()
+ && !(op.code.is_internal_fn ()
+ && conditional_internal_fn_code (internal_fn (op.code))
+ != ERROR_MARK))
+ {
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+ "in-order reduction chain operation not "
+ "supported.\n");
+ return false;
+ }
STMT_VINFO_REDUC_TYPE (reduc_info)
= reduction_type = FOLD_LEFT_REDUCTION;
}
