https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122474
--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> ---
Looking at the PR123053 testcase the guard of the VEC_SHL_INSERT optab check
is false.
if ((double_reduc || neutral_op)
&& !nunits_out.is_constant ()
&& (SLP_TREE_LANES (slp_node) != 1 && !reduc_chain)
&& (!neutral_op
|| !operand_equal_p (neutral_op,
vect_phi_initial_value (reduc_def_phi)))
&& !direct_internal_fn_supported_p (IFN_VEC_SHL_INSERT,
vectype_out, OPTIMIZE_FOR_SPEED))
in particular SLP_TREE_LANES (slp_node) == 1. r16-4558-g1b387bd8978577
added this check, commenting
"This is however not needed if the target can do the reduction using the new
optabs, and the initial reduction value matches the neutral value and we
have one SLP lane while not having a reduction chain."
But the check does not match what is done - instead
&& (!(SLP_TREE_LANES (slp_node) == 1
&& !reduc_chain
&& neutral_op
&& operand_equal_p (neutral_op, ...))
instead would match what the comment in the commit says.
The following patch fixes that particular testcase for me. I'll post it
and see if the risc-v CI still works.
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index aa59cd1a39d..d3bb788d866 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -7653,12 +7653,16 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
/* For double reductions, and for SLP reductions with a neutral value,
we construct a variable-length initial vector by loading a vector
full of the neutral value and then shift-and-inserting the start
- values into the low-numbered elements. */
+ values into the low-numbered elements. This is however not needed
+ if the target can do the reduction using the new optabs, and the initial
+ reduction value matches the neutral value and we have one SLP lane
+ while not having a reduction chain. */
if ((double_reduc || neutral_op)
&& !nunits_out.is_constant ()
- && (SLP_TREE_LANES (slp_node) != 1 && !reduc_chain)
- && (!neutral_op
- || !operand_equal_p (neutral_op,
+ && !(SLP_TREE_LANES (slp_node) == 1
+ && !reduc_chain
+ && neutral_op
+ && operand_equal_p (neutral_op,
vect_phi_initial_value (reduc_def_phi)))
&& !direct_internal_fn_supported_p (IFN_VEC_SHL_INSERT,
vectype_out, OPTIMIZE_FOR_SPEED))
