We had:
if (vec_outside_cost <= 0)
min_profitable_iters = 0;
else
{
min_profitable_iters = ((vec_outside_cost - scalar_outside_cost)
* assumed_vf
- vec_inside_cost * peel_iters_prologue
- vec_inside_cost * peel_iters_epilogue)
/ ((scalar_single_iter_cost * assumed_vf)
- vec_inside_cost);
which can lead to negative min_profitable_iters when the *_outside_costs
are the same and peel_iters_epilogue is nonzero (e.g. if we're peeling
for gaps).
This is tested as part of the patch that adds support for fully-predicated
loops.
Tested on aarch64-linux-gnu (both with and without SVE), x86_64-linux-gnu
and powerpc64le-linux-gnu. OK to install?
Thanks,
Richard
2017-11-08 Richard Sandiford <[email protected]>
Alan Hayward <[email protected]>
David Sherwood <[email protected]>
gcc/
* tree-vect-loop.c (vect_estimate_min_profitable_iters): Make sure
min_profitable_iters doesn't go negative.
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c 2017-11-08 16:35:04.770241799 +0000
+++ gcc/tree-vect-loop.c 2017-11-08 16:47:06.386264822 +0000
@@ -3651,23 +3651,24 @@ vect_estimate_min_profitable_iters (loop
if ((scalar_single_iter_cost * assumed_vf) > (int) vec_inside_cost)
{
- if (vec_outside_cost <= 0)
+ min_profitable_iters = ((vec_outside_cost - scalar_outside_cost)
+ * assumed_vf
+ - vec_inside_cost * peel_iters_prologue
+ - vec_inside_cost * peel_iters_epilogue);
+
+ if (min_profitable_iters <= 0)
min_profitable_iters = 0;
else
- {
- min_profitable_iters = ((vec_outside_cost - scalar_outside_cost)
- * assumed_vf
- - vec_inside_cost * peel_iters_prologue
- - vec_inside_cost * peel_iters_epilogue)
- / ((scalar_single_iter_cost * assumed_vf)
- - vec_inside_cost);
+ {
+ min_profitable_iters /= ((scalar_single_iter_cost * assumed_vf)
+ - vec_inside_cost);
if ((scalar_single_iter_cost * assumed_vf * min_profitable_iters)
<= (((int) vec_inside_cost * min_profitable_iters)
+ (((int) vec_outside_cost - scalar_outside_cost)
* assumed_vf)))
min_profitable_iters++;
- }
+ }
}
/* vector version will never be profitable. */
else
