[OG11][committed][PATCH 19/22] graphite: Tune parameters for OpenACC use

Frederik Harwath frederik@codesourcery.com
Wed Nov 17 16:03:27 GMT 2021


The default values of some parameters that restrict Graphite's
resource usage are too low for many OpenACC codes.  Furthermore,
exceeding the limits does not alwas lead to user-visible diagnostic
messages.

This commit increases the parameter values on OpenACC functions.  The
values were chosen to allow for the analysis of all "kernels" regions
in the SPEC ACCEL v1.3 benchmark suite.  Warnings about exceeded
Graphite-related limits are added to the -fopt-info-missed
output. Those warnings are phrased in a uniform way that intentionally
refers to the "data-dependence analysis" of "OpenACC loops" instead of
"a failure in Graphite" to make them easier to understand for users.

gcc/ChangeLog:

        * graphite-optimize-isl.c (optimize_isl): Adjust
        param_max_isl_operations value for OpenACC functions and add
        special warnings if value gets exceeded.

        * graphite-scop-detection.c (build_scops): Likewise for
        param_graphite_max_arrays_per_scop.

gcc/testsuite/ChangeLog:

        * gcc.dg/goacc/graphite-parameter-1.c: New test.
        * gcc.dg/goacc/graphite-parameter-2.c: New test.
---
 gcc/graphite-optimize-isl.c                   | 35 ++++++++++++++++---
 gcc/graphite-scop-detection.c                 | 28 ++++++++++++++-
 .../gcc.dg/goacc/graphite-parameter-1.c       | 21 +++++++++++
 .../gcc.dg/goacc/graphite-parameter-2.c       | 23 ++++++++++++
 4 files changed, 101 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/goacc/graphite-parameter-1.c
 create mode 100644 gcc/testsuite/gcc.dg/goacc/graphite-parameter-2.c

diff --git a/gcc/graphite-optimize-isl.c b/gcc/graphite-optimize-isl.c
index 019452700a49..4eecbd20b740 100644
--- a/gcc/graphite-optimize-isl.c
+++ b/gcc/graphite-optimize-isl.c
@@ -38,6 +38,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "dumpfile.h"
 #include "tree-vectorizer.h"
 #include "graphite.h"
+#include "graphite-oacc.h"


 /* get_schedule_for_node_st - Improve schedule for the schedule node.
@@ -115,6 +116,14 @@ optimize_isl (scop_p scop, bool oacc_enabled_graphite)
   int old_err = isl_options_get_on_error (scop->isl_context);
   int old_max_operations = isl_ctx_get_max_operations (scop->isl_context);
   int max_operations = param_max_isl_operations;
+
+  /* The default value for param_max_isl_operations is easily exceeded
+     by "kernels" loops in existing OpenACC codes.  Raise the values
+     significantly since analyzing those loops is crucial. */
+  if (param_max_isl_operations == 350000 /* default value */
+      && oacc_function_p (cfun))
+    max_operations = 2000000;
+
   if (max_operations)
     isl_ctx_set_max_operations (scop->isl_context, max_operations);
   isl_options_set_on_error (scop->isl_context, ISL_ON_ERROR_CONTINUE);
@@ -164,11 +173,27 @@ optimize_isl (scop_p scop, bool oacc_enabled_graphite)
          dump_user_location_t loc = find_loop_location
            (scop->scop_info->region.entry->dest->loop_father);
          if (isl_ctx_last_error (scop->isl_context) == isl_error_quota)
-           dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
-                            "loop nest not optimized, optimization timed out "
-                            "after %d operations [--param max-isl-operations]\n",
-                            max_operations);
-         else
+           {
+              if (oacc_function_p (cfun))
+               {
+                 /* Special casing for OpenACC to unify diagnostic messages
+                    here and in graphite-scop-detection.c. */
+                  dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
+                                   "data-dependence analysis of OpenACC loop "
+                                   "nest "
+                                   "failed; try increasing the value of "
+                                   "--param="
+                                   "max-isl-operations=%d.\n",
+                                   max_operations);
+                }
+              else
+                dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
+                                 "loop nest not optimized, optimization timed "
+                                 "out after %d operations [--param "
+                                 "max-isl-operations]\n",
+                                 max_operations);
+            }
+          else
            dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
                             "loop nest not optimized, ISL signalled an error\n");
        }
diff --git a/gcc/graphite-scop-detection.c b/gcc/graphite-scop-detection.c
index 8b41044bce5e..afc955cc97eb 100644
--- a/gcc/graphite-scop-detection.c
+++ b/gcc/graphite-scop-detection.c
@@ -2056,6 +2056,9 @@ determine_openacc_reductions (scop_p scop)
   }
 }

+
+extern dump_user_location_t find_loop_location (class loop *);
+
 /* Find Static Control Parts (SCoP) in the current function and pushes
    them to SCOPS.  */

@@ -2109,6 +2112,11 @@ build_scops (vec<scop_p> *scops)
        }

       unsigned max_arrays = param_graphite_max_arrays_per_scop;
+
+      if (oacc_function_p (cfun)
+          && param_graphite_max_arrays_per_scop == 100 /* default value */)
+        max_arrays = 200;
+
       if (max_arrays > 0
          && scop->drs.length () >= max_arrays)
        {
@@ -2116,7 +2124,16 @@ build_scops (vec<scop_p> *scops)
                       << scop->drs.length ()
                       << " is larger than --param graphite-max-arrays-per-scop="
                       << max_arrays << ".\n");
-         free_scop (scop);
+
+          if (dump_enabled_p () && oacc_function_p (cfun))
+            dump_printf_loc (MSG_MISSED_OPTIMIZATION,
+                             find_loop_location (s->entry->dest->loop_father),
+                             "data-dependence analysis of OpenACC loop nest "
+                             "failed; try increasing the value of --param="
+                             "graphite-max-arrays-per-scop=%d.\n",
+                             max_arrays);
+
+          free_scop (scop);
          continue;
        }

@@ -2129,6 +2146,15 @@ build_scops (vec<scop_p> *scops)
                          << scop_nb_params (scop)
                          << " larger than --param graphite-max-nb-scop-params="
                          << max_dim << ".\n");
+
+          if (dump_enabled_p () && oacc_function_p (cfun))
+            dump_printf_loc (MSG_MISSED_OPTIMIZATION,
+                             find_loop_location (s->entry->dest->loop_father),
+                             "data-dependence analysis of OpenACC loop nest "
+                             "failed; try increasing the value of --param="
+                             "graphite-max-nb-scop-params=%d.\n",
+                             max_dim);
+
          free_scop (scop);
          continue;
        }
diff --git a/gcc/testsuite/gcc.dg/goacc/graphite-parameter-1.c b/gcc/testsuite/gcc.dg/goacc/graphite-parameter-1.c
new file mode 100644
index 000000000000..45adbb3f0e85
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/goacc/graphite-parameter-1.c
@@ -0,0 +1,21 @@
+/* Verify that a warning about an exceeded Graphite parameter gets
+   output as optimization information and not only as a dump message
+   for OpenACC functions. */
+
+/* { dg-additional-options "-O2 -fopt-info-missed --param=graphite-max-arrays-per-scop=1" } */
+
+extern int a[1000];
+extern int b[1000];
+
+void test ()
+{
+#pragma acc parallel loop auto
+/* { dg-missed {data-dependence analysis of OpenACC loop nest failed\; try increasing the value of --param=graphite-max-arrays-per-scop=1.} "" { target *-*-* } .-1  } */
+/* { dg-missed {'auto' loop has not been analyzed \(cf. 'graphite' dumps for more information\).} "" { target *-*-* } .-2 } */
+/* { dg-missed {.*not inlinable.*} "" { target *-*-* } .-3 } */
+  for (int i = 1; i < 995; i++)
+    a[i] = b[i + 5] + b[i - 1];
+}
+
+
+/* { dg-prune-output ".*not inlinable.*"} */
diff --git a/gcc/testsuite/gcc.dg/goacc/graphite-parameter-2.c b/gcc/testsuite/gcc.dg/goacc/graphite-parameter-2.c
new file mode 100644
index 000000000000..f2830cd62db0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/goacc/graphite-parameter-2.c
@@ -0,0 +1,23 @@
+/* Verify that a warning about an exceeded Graphite parameter gets
+   output as optimization information and not only as a dump message
+   for OpenACC functions. */
+
+/* { dg-additional-options "-O2 -fopt-info-missed --param=max-isl-operations=1" } */
+
+void test (int* restrict a, int *restrict b)
+{
+  int i = 1;
+  int j = 1;
+  int m = 0;
+
+#pragma acc parallel loop auto copyin(b) copyout(a) reduction(max:m)
+/* { dg-missed {data-dependence analysis of OpenACC loop nest failed; try increasing the value of --param=max-isl-operations=1.} "" { target *-*-* } .-1  } */
+/* { dg-missed {'auto' loop has not been analyzed \(cf. 'graphite' dumps for more information\).} "" { target *-*-* } .-2 } */
+/* { dg-missed {.*not inlinable.*} "" { target *-*-* } .-3 } */
+  for (i = 1; i < 995; i++)
+    {
+      int x = b[i] * 2;
+      for (j = 1; j < 995; j++)
+        m = m + a[i] + x;
+    }
+}
--
2.33.0

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