Commit r16-4079-gc8bd7b2d550 added dispatch scheduling for AArch64.
However, in choose_ready(), the dispatch scheduling path was only
reachable when dfa_lookahead <= 0, or when the first ready insn was a
SCHED_GROUP_P insn. Commit r16-6155-g40d0f79577e then made SCHED_GROUP_P
insns bypass dispatch scheduling to prevent fusion pairs from being
split. As a result, the DFA lookahead path is preferred and dispatch
scheduling is effectively disabled for AArch64 multi-issue cores.
dfa_lookahead comes from the hook first_cycle_multipass_dfa_lookahead.
In current AArch64 implementation, it returns a positive issue rate
value for multi-issue cores unless sched_fusion is true. This patch adds
an IS_DISPATCH_ON check to that hook implementation so that the dispatch
scheduling path is reachable on dispatch-enabled AArch64 cores.
Bootstrapped and tested on aarch64-linux-gnu.
gcc/ChangeLog:
* config/aarch64/aarch64.cc
(aarch64_sched_first_cycle_multipass_dfa_lookahead): Return 0
when dispatch scheduling is enabled.
gcc/testsuite/ChangeLog:
* gcc.target/aarch64/dispatch_sched_1.c: New test.
---
gcc/config/aarch64/aarch64.cc | 8 ++++++--
gcc/testsuite/gcc.target/aarch64/dispatch_sched_1.c | 13 +++++++++++++
2 files changed, 19 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/aarch64/dispatch_sched_1.c
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 9dd19d81d7b..7d0ecaa1340 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -17191,9 +17191,13 @@ aarch64_sched_variable_issue (FILE *, int, rtx_insn
*insn, int more)
static int
aarch64_sched_first_cycle_multipass_dfa_lookahead (void)
{
- int issue_rate = aarch64_sched_issue_rate ();
+ /* Do not use DFA lookahead during sched_fusion or when dispatch
+ scheduling is enabled. */
+ if (sched_fusion || aarch64_sched_dispatch (NULL, IS_DISPATCH_ON))
+ return 0;
- return issue_rate > 1 && !sched_fusion ? issue_rate : 0;
+ int issue_rate = aarch64_sched_issue_rate ();
+ return issue_rate > 1 ? issue_rate : 0;
}
diff --git a/gcc/testsuite/gcc.target/aarch64/dispatch_sched_1.c
b/gcc/testsuite/gcc.target/aarch64/dispatch_sched_1.c
new file mode 100644
index 00000000000..c2cb74e750d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/dispatch_sched_1.c
@@ -0,0 +1,13 @@
+/* Check DFA lookahead is not reached when dispatch scheduling is enabled. */
+/* { dg-do compile } */
+/* { dg-options "-O3 -mcpu=neoverse-v2 -fdump-rtl-sched2-details
-fsched-verbose=2" } */
+
+void
+foo (int *restrict a, int *restrict b, int *restrict c, int n)
+{
+#pragma GCC unroll 64
+ for (int i = 0; i < n; i++)
+ c[i] += a[i] * b[i];
+}
+
+/* { dg-final { scan-rtl-dump-not "max_issue among" "sched2" } } */
--
2.43.0
