When we vectorize fold-left reductions with partial vectors but
no target operation available we use a vector conditional to force
excess elements to zero. But that doesn't correctly preserve
the sign of zero. The following patch disables partial vector
support in that case.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
Does this look OK? With -frounding-math -fno-signed-zeros we are
happily using the masking again, but that's OK, right? An additional
+ 0.0 shouldn't do anything here.
Thanks,
Richard.
PR tree-optimization/110979
* tree-vect-loop.cc (vectorizable_reduction): For
FOLD_LEFT_REDUCTION without target support make sure
we don't need to honor signed zeros.
* gcc.dg/torture/pr110979.c: New testcase.
---
gcc/testsuite/gcc.dg/torture/pr110979.c | 25 +++++++++++++++++++++++++
gcc/tree-vect-loop.cc | 11 +++++++++++
2 files changed, 36 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/torture/pr110979.c
diff --git a/gcc/testsuite/gcc.dg/torture/pr110979.c
b/gcc/testsuite/gcc.dg/torture/pr110979.c
new file mode 100644
index 00000000000..c25ad7a8a31
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr110979.c
@@ -0,0 +1,25 @@
+/* { dg-do run } */
+/* { dg-additional-options "--param vect-partial-vector-usage=2" } */
+
+#define FLT double
+#define N 20
+
+__attribute__((noipa))
+FLT
+foo3 (FLT *a)
+{
+ FLT sum = -0.0;
+ for (int i = 0; i != N; i++)
+ sum += a[i];
+ return sum;
+}
+
+int main()
+{
+ FLT a[N];
+ for (int i = 0; i != N; i++)
+ a[i] = -0.0;
+ if (!__builtin_signbit(foo3(a)))
+ __builtin_abort();
+ return 0;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index bf8d677b584..741b5c20389 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -8037,6 +8037,17 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
" no conditional operation is available.\n");
LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
}
+ else if (reduction_type == FOLD_LEFT_REDUCTION
+ && reduc_fn == IFN_LAST
+ && FLOAT_TYPE_P (vectype_in)
+ && HONOR_SIGNED_ZEROS (vectype_in))
+ {
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+ "can't operate on partial vectors because"
+ " signed zeros need to be handled.\n");
+ LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
+ }
else
{
internal_fn mask_reduc_fn
--
2.35.3
