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* [gcc/devel/omp/gcc-11] graphite: Extend SCoP detection dump output
@ 2021-11-17 8:17 Frederik Harwath
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From: Frederik Harwath @ 2021-11-17 8:17 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:30bc9660cf1df386bbe41d0fd97e46d31c2213c8
commit 30bc9660cf1df386bbe41d0fd97e46d31c2213c8
Author: Frederik Harwath <frederik@codesourcery.com>
Date: Tue Nov 16 16:11:21 2021 +0100
graphite: Extend SCoP detection dump output
Extend dump output to make understanding why Graphite rejects to
include a loop in a SCoP easier (for GCC developers).
ChangeLog:
* graphite-scop-detection.c (scop_detection::can_represent_loop):
Output reason for failure to dump file.
(scop_detection::harmful_loop_in_region): Likewise.
(scop_detection::graphite_can_represent_expr): Likewise.
(scop_detection::stmt_has_simple_data_refs_p): Likewise.
(scop_detection::stmt_simple_for_scop_p): Likewise.
(print_sese_loop_numbers): New function.
(scop_detection::add_scop): Use from here to print loops in
rejected SCoP.
Diff:
---
gcc/graphite-scop-detection.c | 188 ++++++++++++++++++++++++++++++++++++------
1 file changed, 165 insertions(+), 23 deletions(-)
diff --git a/gcc/graphite-scop-detection.c b/gcc/graphite-scop-detection.c
index 3e729b159b0..46c470210d0 100644
--- a/gcc/graphite-scop-detection.c
+++ b/gcc/graphite-scop-detection.c
@@ -69,12 +69,27 @@ public:
fprintf (output.dump_file, "%d", i);
return output;
}
+
friend debug_printer &
operator<< (debug_printer &output, const char *s)
{
fprintf (output.dump_file, "%s", s);
return output;
}
+
+ friend debug_printer &
+ operator<< (debug_printer &output, gimple* stmt)
+ {
+ print_gimple_stmt (output.dump_file, stmt, 0, TDF_VOPS | TDF_MEMSYMS);
+ return output;
+ }
+
+ friend debug_printer &
+ operator<< (debug_printer &output, tree t)
+ {
+ print_generic_expr (output.dump_file, t, TDF_SLIM);
+ return output;
+ }
} dp;
#define DEBUG_PRINT(args) do \
@@ -506,6 +521,24 @@ scop_detection::merge_sese (sese_l first, sese_l second) const
return combined;
}
+/* Print the loop numbers of the loops contained
+ in SESE to FILE. */
+
+static void
+print_sese_loop_numbers (FILE *file, sese_l sese)
+{
+ loop_p loop;
+ bool printed = false;
+ FOR_EACH_LOOP (loop, 0)
+ {
+ if (loop_in_sese_p (loop, sese))
+ fprintf (file, "%d, ", loop->num);
+ printed = true;
+ }
+ if (printed)
+ fprintf (file, "\b\b");
+}
+
/* Build scop outer->inner if possible. */
void
@@ -519,8 +552,13 @@ scop_detection::build_scop_depth (loop_p loop)
if (! next
|| harmful_loop_in_region (next))
{
- if (s)
- add_scop (s);
+ if (next)
+ DEBUG_PRINT (
+ dp << "[scop-detection] Discarding SCoP on loops ";
+ print_sese_loop_numbers (dump_file, next);
+ dp << " because of harmful loops\n";);
+ if (s)
+ add_scop (s);
build_scop_depth (loop);
s = invalid_sese;
}
@@ -560,14 +598,62 @@ scop_detection::can_represent_loop (loop_p loop, sese_l scop)
|| !single_pred_p (loop->latch)
|| exit->src != single_pred (loop->latch)
|| !empty_block_p (loop->latch))
- return false;
+ {
+ DEBUG_PRINT (dp << "[can_represent_loop-fail] Loop shape unsupported.\n");
+ return false;
+ }
+
+ bool edge_irreducible
+ = loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP;
+ if (edge_irreducible)
+ {
+ DEBUG_PRINT (
+ dp << "[can_represent_loop-fail] Loop is not a natural loop.\n");
+ return false;
+ }
+
+ bool niter_is_unconditional = number_of_iterations_exit (loop,
+ single_exit (loop),
+ &niter_desc, 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))
- && !chrec_contains_undetermined (niter)
- && graphite_can_represent_expr (scop, loop, niter);
+ if (!niter_is_unconditional)
+ {
+ DEBUG_PRINT (
+ dp << "[can_represent_loop-fail] Loop niter not unconditional.\n"
+ << "Condition: " << niter_desc.assumptions << "\n");
+ return false;
+ }
+
+ niter = number_of_latch_executions (loop);
+ if (!niter)
+ {
+ DEBUG_PRINT (dp << "[can_represent_loop-fail] Loop niter unknown.\n");
+ return false;
+ }
+ if (!niter_desc.control.no_overflow)
+ {
+ DEBUG_PRINT (dp << "[can_represent_loop-fail] Loop niter can overflow.\n");
+ return false;
+ }
+
+ bool undetermined_coefficients = chrec_contains_undetermined (niter);
+ if (undetermined_coefficients)
+ {
+ DEBUG_PRINT (dp << "[can_represent_loop-fail] "
+ << "Loop niter chrec contains undetermined coefficients.\n");
+ return false;
+ }
+
+ bool can_represent_expr = graphite_can_represent_expr (scop, loop, niter);
+ if (!can_represent_expr)
+ {
+ DEBUG_PRINT (dp << "[can_represent_loop-fail] "
+ << "Loop niter expression cannot be represented: "
+ << niter << "\n");
+ return false;
+ }
+
+ return true;
}
/* Return true when BEGIN is the preheader edge of a loop with a single exit
@@ -640,6 +726,16 @@ scop_detection::add_scop (sese_l s)
scops.safe_push (s);
DEBUG_PRINT (dp << "[scop-detection] Adding SCoP: "; print_sese (dump_file, s));
+
+ if (dump_file && dump_flags & TDF_DETAILS)
+ {
+ loop_p loop;
+ fprintf (dump_file, "Loops in SCoP: ");
+ FOR_EACH_LOOP (loop, 0)
+ if (loop_in_sese_p (loop, s))
+ fprintf (dump_file, "%d ", loop->num);
+ fprintf (dump_file, "\n");
+ }
}
/* Return true when a statement in SCOP cannot be represented by Graphite. */
@@ -665,7 +761,11 @@ scop_detection::harmful_loop_in_region (sese_l scop) const
/* The basic block should not be part of an irreducible loop. */
if (bb->flags & BB_IRREDUCIBLE_LOOP)
- return true;
+ {
+ DEBUG_PRINT (dp << "[scop-detection-fail] Found bb in irreducible "
+ "loop.\n");
+ return true;
+ }
/* Check for unstructured control flow: CFG not generated by structured
if-then-else. */
@@ -676,7 +776,11 @@ scop_detection::harmful_loop_in_region (sese_l scop) const
FOR_EACH_EDGE (e, ei, bb->succs)
if (!dominated_by_p (CDI_POST_DOMINATORS, bb, e->dest)
&& !dominated_by_p (CDI_DOMINATORS, e->dest, bb))
- return true;
+ {
+ DEBUG_PRINT (dp << "[scop-detection-fail] Found unstructured "
+ "control flow.\n");
+ return true;
+ }
}
/* Collect all loops in the current region. */
@@ -688,7 +792,10 @@ scop_detection::harmful_loop_in_region (sese_l scop) const
for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
!gsi_end_p (gsi); gsi_next (&gsi))
if (!stmt_simple_for_scop_p (scop, gsi_stmt (gsi), bb))
- return true;
+ {
+ DEBUG_PRINT (dp << "[scop-detection-fail] Found harmful statement.\n");
+ return true;
+ }
for (basic_block dom = first_dom_son (CDI_DOMINATORS, bb);
dom;
@@ -731,9 +838,11 @@ scop_detection::harmful_loop_in_region (sese_l scop) const
&& ! loop_nest_has_data_refs (loop))
{
DEBUG_PRINT (dp << "[scop-detection-fail] loop_" << loop->num
- << "does not have any data reference.\n");
+ << " does not have any data reference.\n");
return true;
}
+
+ DEBUG_PRINT (dp << "[scop-detection] loop_" << loop->num << " is harmless.\n");
}
return false;
@@ -922,7 +1031,21 @@ scop_detection::graphite_can_represent_expr (sese_l scop, loop_p loop,
tree expr)
{
tree scev = cached_scalar_evolution_in_region (scop, loop, expr);
- return graphite_can_represent_scev (scop, scev);
+ bool can_represent = graphite_can_represent_scev (scop, scev);
+
+ if (!can_represent)
+ {
+ if (dump_file)
+ {
+ fprintf (dump_file, "[graphite_can_represent_expr] Cannot represent "
+ "scev \"");
+ print_generic_expr (dump_file, scev, TDF_SLIM);
+ fprintf (dump_file, "\" of expression ");
+ print_generic_expr (dump_file, expr, TDF_SLIM);
+ fprintf (dump_file, " in loop %d\n", loop->num);
+ }
+ }
+ return can_represent;
}
/* Return true if the data references of STMT can be represented by Graphite.
@@ -938,7 +1061,11 @@ scop_detection::stmt_has_simple_data_refs_p (sese_l scop, gimple *stmt)
auto_vec<data_reference_p> drs;
if (! graphite_find_data_references_in_stmt (nest, loop, stmt, &drs))
- return false;
+ {
+ DEBUG_PRINT (dp <<
+ "[stmt_has_simple_data_refs_p] Unanalyzable statement.\n");
+ return false;
+ }
int j;
data_reference_p dr;
@@ -946,7 +1073,12 @@ scop_detection::stmt_has_simple_data_refs_p (sese_l scop, gimple *stmt)
{
for (unsigned i = 0; i < DR_NUM_DIMENSIONS (dr); ++i)
if (! graphite_can_represent_scev (scop, DR_ACCESS_FN (dr, i)))
- return false;
+ {
+ DEBUG_PRINT (dp << "[stmt_has_simple_data_refs_p] Cannot "
+ "represent access function SCEV: "
+ << DR_ACCESS_FN (dr, i) << "\n");
+ return false;
+ }
}
return true;
@@ -1027,14 +1159,24 @@ scop_detection::stmt_simple_for_scop_p (sese_l scop, gimple *stmt,
for (unsigned i = 0; i < 2; ++i)
{
tree op = gimple_op (stmt, i);
- if (!graphite_can_represent_expr (scop, loop, op)
- /* We can only constrain on integer type. */
- || ! INTEGRAL_TYPE_P (TREE_TYPE (op)))
+ if (!graphite_can_represent_expr (scop, loop, op))
+ {
+ DEBUG_PRINT (dump_printf_loc (MSG_MISSED_OPTIMIZATION, stmt,
+ "[scop-detection-fail] "
+ "Graphite cannot represent cond "
+ "stmt operator expression.\n"));
+ DEBUG_PRINT (dp << op << "\n");
+
+ return false;
+ }
+
+ if (! INTEGRAL_TYPE_P (TREE_TYPE (op)))
{
- DEBUG_PRINT (dp << "[scop-detection-fail] "
- << "Graphite cannot represent stmt:\n";
- print_gimple_stmt (dump_file, stmt, 0,
- TDF_VOPS | TDF_MEMSYMS));
+ DEBUG_PRINT (dump_printf_loc (MSG_MISSED_OPTIMIZATION, stmt,
+ "[scop-detection-fail] "
+ "Graphite cannot represent cond "
+ "statement operator. "
+ "Type must be integral.\n"));
return false;
}
}
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