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Fix overly restrictive live-lane extraction replacement

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The following fixes a regression introduced by r11-5542 which
restricts replacing uses of live original defs of now vectorized
stmts to when that does not require new loop-closed PHIs to be
inserted.  That restriction keeps the original scalar definition
live which is sub-optimal and also not reflected in costing.

The particular case the following fixes can be seen in
gcc.dg/vect/bb-slp-57.c is the case where we are replacing an
existing loop closed PHI argument.

	PR tree-optimization/98064
	* tree-vect-loop.cc (vectorizable_live_operation): Do
	not restrict replacing uses in a LC PHI.

	* gcc.dg/vect/bb-slp-57.c: Verify we do not keep original
	stmts live.
This commit is contained in:
Richard Biener
2026-03-05 11:39:38 +01:00
committed by Richard Biener
parent 8b39ec7074
commit c1926449ca
2 changed files with 29 additions and 19 deletions
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1
gcc/testsuite/gcc.dg/vect/bb-slp-57.c
View File

@@ -36,3 +36,4 @@ void l()
/* { dg-final { scan-tree-dump-times "transform load" 1 "slp1" { target { { x86_64-*-* i?86-*-* } && lp64 } } } } */
/* { dg-final { scan-tree-dump "optimized: basic block" "slp1" { target { { x86_64-*-* i?86-*-* } && lp64 } } } } */
/* { dg-final { scan-tree-dump-not "missed: Using original scalar computation" "slp1" } } */

47
gcc/tree-vect-loop.cc
View File

@@ -10441,26 +10441,35 @@ vectorizable_live_operation (vec_info *vinfo, stmt_vec_info stmt_info,
"def\n");
continue;
}
/* ??? It can also happen that we end up pulling a def into
a loop where replacing out-of-loop uses would require
a new LC SSA PHI node. Retain the original scalar in
those cases as well. PR98064. */
if (TREE_CODE (new_tree) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (new_tree)
&& (gimple_bb (use_stmt)->loop_father
!= gimple_bb (vec_stmt)->loop_father)
&& !flow_loop_nested_p (gimple_bb (vec_stmt)->loop_father,
gimple_bb (use_stmt)->loop_father))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"Using original scalar computation for "
"live lane because there is an out-of-loop "
"definition for it\n");
continue;
}
FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
SET_USE (use_p, new_tree);
{
/* ??? It can also happen that we end up pulling a def into
a loop where replacing out-of-loop uses would require
a new LC SSA PHI node. Retain the original scalar in
those cases as well. PR98064. */
edge e;
if (TREE_CODE (new_tree) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (new_tree)
&& (gimple_bb (use_stmt)->loop_father
!= gimple_bb (vec_stmt)->loop_father)
/* But a replacemend in a LC PHI is OK. This happens
in gcc.dg/vect/bb-slp-57.c for example. */
&& (gimple_code (use_stmt) != GIMPLE_PHI
|| (((e = phi_arg_edge_from_use (use_p)), true)
&& !loop_exit_edge_p
(gimple_bb (vec_stmt)->loop_father, e)))
&& !flow_loop_nested_p (gimple_bb (vec_stmt)->loop_father,
gimple_bb (use_stmt)->loop_father))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"Using original scalar computation for "
"live lane because there is an "
"out-of-loop definition for it\n");
continue;
}
SET_USE (use_p, new_tree);
}
update_stmt (use_stmt);
}
}