public inbox for gcc-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc r12-986] [OpenACC privatization] Explain OpenACC privatization candidate selection [PR90115]
@ 2021-05-21 18:54 Thomas Schwinge
0 siblings, 0 replies; only message in thread
From: Thomas Schwinge @ 2021-05-21 18:54 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:5a0fe1f6c4ad0e50bf4684e723ae2ba17d94c9e4
commit r12-986-g5a0fe1f6c4ad0e50bf4684e723ae2ba17d94c9e4
Author: Thomas Schwinge <thomas@codesourcery.com>
Date: Thu May 20 15:55:18 2021 +0200
[OpenACC privatization] Explain OpenACC privatization candidate selection [PR90115]
gcc/
PR middle-end/90115
* omp-low.c (oacc_privatization_candidate_p): New function.
(oacc_privatization_scan_clause_chain)
(oacc_privatization_scan_decl_chain): Use it. Also
'gcc_checking_assert' that we're not seeing duplicates.
Diff:
---
gcc/omp-low.c | 45 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 42 insertions(+), 3 deletions(-)
diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index a86c6c1e82c..577676b2a16 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -10144,6 +10144,36 @@ lower_omp_for_lastprivate (struct omp_for_data *fd, gimple_seq *body_p,
}
}
+/* OpenACC privatization.
+
+ Or, in other words, *sharing* at the respective OpenACC level of
+ parallelism.
+
+ From a correctness perspective, a non-addressable variable can't be accessed
+ outside the current thread, so it can go in a (faster than shared memory)
+ register -- though that register may need to be broadcast in some
+ circumstances. A variable can only meaningfully be "shared" across workers
+ or vector lanes if its address is taken, e.g. by a call to an atomic
+ builtin.
+
+ From an optimisation perspective, the answer might be fuzzier: maybe
+ sometimes, using shared memory directly would be faster than
+ broadcasting. */
+
+static bool
+oacc_privatization_candidate_p (const tree decl)
+{
+ bool res = true;
+
+ if (res && !VAR_P (decl))
+ res = false;
+
+ if (res && !TREE_ADDRESSABLE (decl))
+ res = false;
+
+ return res;
+}
+
/* Scan CLAUSES for candidates for adjusting OpenACC privatization level in
CTX. */
@@ -10154,8 +10184,12 @@ oacc_privatization_scan_clause_chain (omp_context *ctx, tree clauses)
if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_PRIVATE)
{
tree decl = OMP_CLAUSE_DECL (c);
- if (VAR_P (decl) && TREE_ADDRESSABLE (decl))
- ctx->oacc_privatization_candidates.safe_push (decl);
+
+ if (!oacc_privatization_candidate_p (decl))
+ continue;
+
+ gcc_checking_assert (!ctx->oacc_privatization_candidates.contains (decl));
+ ctx->oacc_privatization_candidates.safe_push (decl);
}
}
@@ -10166,8 +10200,13 @@ static void
oacc_privatization_scan_decl_chain (omp_context *ctx, tree decls)
{
for (tree decl = decls; decl; decl = DECL_CHAIN (decl))
- if (VAR_P (decl) && TREE_ADDRESSABLE (decl))
+ {
+ if (!oacc_privatization_candidate_p (decl))
+ continue;
+
+ gcc_checking_assert (!ctx->oacc_privatization_candidates.contains (decl));
ctx->oacc_privatization_candidates.safe_push (decl);
+ }
}
/* Callback for walk_gimple_seq. Find #pragma omp scan statement. */
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2021-05-21 18:54 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-21 18:54 [gcc r12-986] [OpenACC privatization] Explain OpenACC privatization candidate selection [PR90115] Thomas Schwinge
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).