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tree-optimization/115372 - failed store-lanes in some cases

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The gcc.target/riscv/rvv/autovec/struct/struct_vect-4.c testcase shows
that we sometimes fail to use store-lanes even though it should be
profitable.  We're currently relying on vect_slp_prefer_store_lanes_p
at the point we run into the first SLP discovery mismatch with obviously
limited information.  For the case at hand we have 3, 5 or 7 lanes
of VnDImode [2, 2] vectors with the first mismatch at lane 2 so the
new group size is 1.  The heuristic says that might be an OK split
given the rest is a multiple of the vector lanes.  Now we continue
discovery but in the end mismatches result in uniformly single-lane
SLP instances which we can handle via interleaving but of course are
prime candidates for store-lanes.  The following patch re-assesses
with the extra knowledge now just relying on the fact whether the
target supports store-lanes for the given group size.

	PR tree-optimization/115372
	* tree-vect-slp.cc (vect_build_slp_instance): Compute the
	uniform, if, number of lanes of the RHS sub-graphs feeding
	the store and if uniformly one, use store-lanes if the target
	supports that.
This commit is contained in:
Richard Biener 2024-09-20 15:07:24 +02:00 • committed by Richard Biener
parent 618871ff09
commit f594008dcc
1 changed files with 18 additions and 0 deletions
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18
gcc/tree-vect-slp.cc
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@ -3957,6 +3957,7 @@ vect_build_slp_instance (vec_info *vinfo,
/* Calculate the unrolling factor based on the smallest type. */
poly_uint64 unrolling_factor = 1;
unsigned int rhs_common_nlanes = 0;
unsigned int start = 0, end = i;
while (start < group_size)
{
@ -3978,6 +3979,10 @@ vect_build_slp_instance (vec_info *vinfo,
calculate_unrolling_factor
(max_nunits, end - start));
rhs_nodes.safe_push (node);
if (start == 0)
rhs_common_nlanes = SLP_TREE_LANES (node);
else if (rhs_common_nlanes != SLP_TREE_LANES (node))
rhs_common_nlanes = 0;
start = end;
if (want_store_lanes || force_single_lane)
end = start + 1;
@ -4015,6 +4020,19 @@ vect_build_slp_instance (vec_info *vinfo,
}
}
/* Now re-assess whether we want store lanes in case the
discovery ended up producing all single-lane RHSs. */
if (rhs_common_nlanes == 1
&& ! STMT_VINFO_GATHER_SCATTER_P (stmt_info)
&& ! STMT_VINFO_STRIDED_P (stmt_info)
&& compare_step_with_zero (vinfo, stmt_info) > 0
&& (vect_store_lanes_supported (SLP_TREE_VECTYPE (rhs_nodes[0]),
group_size,
SLP_TREE_CHILDREN
(rhs_nodes[0]).length () != 1)
!= IFN_LAST))
want_store_lanes = true;
/* Now we assume we can build the root SLP node from all stores. */
if (want_store_lanes)
{