This commit concerns loops in OpenACC "kernels" region that have been marked
up with an explicit "independent" clause by the user, but for which Graphite
found data dependences. A discussion on the private internal OpenACC mailing
list suggested that warning the user about the dependences woud be a more
acceptable solution than reverting the user's decision. This behavior is
implemented by the present commit.
gcc/ChangeLog:
* common.opt: Add flag Wopenacc-false-independent.
* omp-offload.c (oacc_loop_warn_if_false_independent): New function.
(oacc_loop_fixed_partitions): Call from here.
---
gcc/common.opt | 5 +++++
gcc/omp-offload.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+)
diff --git a/gcc/common.opt b/gcc/common.opt
index b6c46ab63e34..ec76a88f14e3 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -850,6 +850,11 @@ Wtsan
Common Var(warn_tsan) Init(1) Warning
Warn about unsupported features in ThreadSanitizer.
+Wopenacc-false-independent
+Common Var(warn_openacc_false_independent) Init(1) Warning
+Warn in case a loop in an OpenACC \"kernels\" region has an \"independent\"
+clause but analysis shows that it has loop-carried dependences.
+
Xassembler
Driver Separate
diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c
index 3458a1acbceb..36dde11f5955 100644
--- a/gcc/omp-offload.c
+++ b/gcc/omp-offload.c
@@ -1900,6 +1900,51 @@ oacc_loop_transform_auto_into_independent (oacc_loop
*loop)
return true;
}
+/* Emit a warning if LOOP has an "independent" clause but Graphite's
+ analysis shows that it has data dependences. Note that we respect
+ the user's explicit decision to parallelize the loop but we
+ nevertheless warn that this decision could be wrong. */
+
+static void
+oacc_loop_warn_if_false_independent (oacc_loop *loop)
+{
+ if (!optimize)
+ return;
+
+ if (loop->routine)
+ return;
+
+ /* TODO Warn about "auto" & "independent" in "parallel" regions? */
+ if (!oacc_parallel_kernels_graphite_fun_p ())
+ return;
+
+ if (!(loop->flags & OLF_INDEPENDENT))
+ return;
+
+ bool analyzed = false;
+ bool can_be_parallel = oacc_loop_can_be_parallel_p (loop, analyzed);
+ loop_p cfg_loop = oacc_loop_get_cfg_loop (loop);
+
+ if (cfg_loop && cfg_loop->inner && !analyzed)
+ {
+ if (dump_enabled_p ())
+ {
+ const dump_user_location_t loc
+ = dump_user_location_t::from_location_t (loop->loc);
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
+ "'independent' loop in 'kernels' region has not been
"
+ "analyzed (cf. 'graphite' "
+ "dumps for more information).\n");
+ }
+ return;
+ }
+
+ if (!can_be_parallel)
+ warning_at (loop->loc, 0,
+ "loop has \"independent\" clause but data dependences were "
+ "found.");
+}
+
/* Walk the OpenACC loop hierarchy checking and assigning the
programmer-specified partitionings. OUTER_MASK is the partitioning
this loop is contained within. Return mask of partitioning
@@ -1951,6 +1996,10 @@ oacc_loop_fixed_partitions (oacc_loop *loop, unsigned
outer_mask)
}
}
+ /* TODO Is this flag needed? Perhaps use -Wopenacc-parallelism? */
+ if (warn_openacc_false_independent)
+ oacc_loop_warn_if_false_independent (loop);
+
if (maybe_auto && (loop->flags & OLF_INDEPENDENT))
{
loop->flags |= OLF_AUTO;
--
2.33.0
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