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tree-optimization/103237 - avoid vectorizing unhandled double reductions

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Double reductions which have multiple LC PHIs in the inner loop
are not handled correctly during transformation since those PHIs
are not properly classified as reduction.  The following disables
vectorizing them.

2021-11-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/103237
	* tree-vect-loop.c (vect_is_simple_reduction): Fail for
	double reductions with multiple inner loop LC PHI nodes.

	* gcc.dg/torture/pr103237.c: New testcase.
This commit is contained in:
Richard Biener 2021-11-15 11:37:56 +01:00
parent 4d281ff7dd
commit 220bd61874
2 changed files with 35 additions and 0 deletions
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24
gcc/testsuite/gcc.dg/torture/pr103237.c Normal file
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@ -0,0 +1,24 @@
/* { dg-do run } */
/* { dg-additional-options "-ftree-vectorize" } */
int g1;
unsigned int g2 = -1U;
static void __attribute__((noipa))
func_1()
{
int *l_1 = &g1;
for (int g3a = 0; g3a != 4; g3a++)
for (int l_2 = 0; l_2 <= 3; l_2++)
{
unsigned int *l_3 = &g2;
*l_1 = *l_3 ^= 1;
}
}
int
main()
{
func_1();
if (g1 != -1)
__builtin_abort ();
return 0;
}

11
gcc/tree-vect-loop.c
View file

@ -3567,6 +3567,17 @@ vect_is_simple_reduction (loop_vec_info loop_info, stmt_vec_info phi_info,
return def_stmt_info;
}
/* When the inner loop of a double reduction ends up with more than
one loop-closed PHI we have failed to classify alternate such
PHIs as double reduction, leading to wrong code. See PR103237. */
if (inner_loop_of_double_reduc && lcphis.length () != 1)
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"unhandle double reduction\n");
return NULL;
}
/* If this isn't a nested cycle or if the nested cycle reduction value
is used ouside of the inner loop we cannot handle uses of the reduction
value. */