https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86865
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |sebpop at gmail dot com
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, actually the original AST already doesn't match the original GIMPLE:
[scheduler] original ast:
for (int c0 = 0; c0 <= 1; c0 += 1) {
S_3(c0);
for (int c1 = 0; c1 <= 7; c1 += 1)
S_4(c0, c1);
S_9(c0);
}
vs. GIMPLE
<bb 6> [local count: 134036760]:
# prephitmp_8 = PHI <0(2), _1(9)>
if (prephitmp_8 >= 0)
goto <bb 3>; [89.00%]
else
goto <bb 7>; [11.00%] <exit>
<bb 3> [local count: 119292716]:
sa = {};
<bb 4> [local count: 954449108]:
# us_18 = PHI <0(3), us_11(8)>
yt[us_18] = 0;
us_11 = us_18 + 1;
if (us_11 != 8)
goto <bb 8>; [87.50%]
else
goto <bb 5>; [12.50%]
<bb 8> [local count: 835156388]:
goto <bb 4>; [100.00%]
<bb 5> [local count: 119292717]:
<bb 9> [local count: 119292717]:
_1 = prephitmp_8 + -1;
xy = _1;
goto <bb 6>;
here the number of latch executions is one (and BB 9 and thus xy = _1
executes once) while the ISL AST has S_9 executed twice. So the
bug is in how we translate GIMPLE to ISL which assumes do {} while
style loops rather than adjusting iteration domains. I've never
groked the code there fully so the "easiest" way out would be to
require do {} while style loops similar to what the vectorizer
requires.
Index: gcc/graphite-scop-detection.c
===================================================================
--- gcc/graphite-scop-detection.c (revision 268010)
+++ gcc/graphite-scop-detection.c (working copy)
@@ -555,8 +555,15 @@ scop_detection::can_represent_loop (loop
tree niter;
struct tree_niter_desc niter_desc;
- return single_exit (loop)
- && !(loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP)
+ /* We can only handle do {} while () style loops correctly. */
+ edge exit = single_exit (loop);
+ if (!exit
+ || !single_pred_p (loop->latch)
+ || exit->src != single_pred (loop->latch)
+ || !empty_block_p (loop->latch))
+ return false;
+
+ return !(loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP)
&& number_of_iterations_exit (loop, single_exit (loop), &niter_desc,
false)
&& niter_desc.control.no_overflow
&& (niter = number_of_latch_executions (loop))
which in turn FAILs
FAIL: gcc.dg/graphite/scop-21.c scan-tree-dump-times graphite "number of SCoPs:
1" 1
FAIL: gcc.dg/graphite/pr69728.c scan-tree-dump graphite "loop nest optimized"
where loop header copying is "broken" by jump threading for scop-21.c.
