Scheduling should never move very expensive instructions to places they
are executed more frequently. This patch fixes that, reducing the
execution time of c-ray by over 40% (I tested on a BE Power7 system).
This introduces a new target hook sched.can_speculate_insn which returns
whether the scheduler is allowed to speculate a given instruction. The
rs6000 implementation disallows all divide and square root instructions.
Bootstrapped and tested on powerpc64-linux {-m32,-m64}. Is this okay
for trunk?
Segher
2017-02-03 Segher Boessenkool <[email protected]>
PR rtl-optimization/68664
* target.def (can_speculate_insn): New hook.
* doc/tm.texi.in (TARGET_SCHED_CAN_SPECULATE_INSN): New hook.
* doc/tm.texi: Regenerate.
* sched-rgn.c (can_schedule_ready_p): Use the new hook.
* config/rs6000/rs6000.c (TARGET_SCHED_CAN_SPECULATE_INSN): New macro.
(rs6000_sched_can_speculate_insn): New function.
---
gcc/config/rs6000/rs6000.c | 20 ++++++++++++++++++++
gcc/doc/tm.texi | 6 ++++++
gcc/doc/tm.texi.in | 2 ++
gcc/sched-rgn.c | 19 +++++++++++++------
gcc/target.def | 7 +++++++
5 files changed, 48 insertions(+), 6 deletions(-)
diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 98e5f91..5e85858 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1608,6 +1608,9 @@ static const struct attribute_spec
rs6000_attribute_table[] =
#undef TARGET_SCHED_FREE_SCHED_CONTEXT
#define TARGET_SCHED_FREE_SCHED_CONTEXT rs6000_free_sched_context
+#undef TARGET_SCHED_CAN_SPECULATE_INSN
+#define TARGET_SCHED_CAN_SPECULATE_INSN rs6000_sched_can_speculate_insn
+
#undef TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD
#define TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD rs6000_builtin_mask_for_load
#undef TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT
@@ -34986,6 +34989,23 @@ rs6000_free_sched_context (void *_sc)
free (_sc);
}
+static bool
+rs6000_sched_can_speculate_insn (rtx_insn *insn)
+{
+ switch (get_attr_type (insn))
+ {
+ case TYPE_DIV:
+ case TYPE_SDIV:
+ case TYPE_DDIV:
+ case TYPE_VECDIV:
+ case TYPE_SSQRT:
+ case TYPE_DSQRT:
+ return false;
+
+ default:
+ return true;
+ }
+}
/* Length in units of the trampoline for entering a nested function. */
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 909589c..1963402 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -7000,6 +7000,12 @@ The structure *@var{spec_info} should be filled in by
the target.
The structure describes speculation types that can be used in the scheduler.
@end deftypefn
+@deftypefn {Target Hook} bool TARGET_SCHED_CAN_SPECULATE_INSN (rtx_insn
*@var{insn})
+Some instructions should never be speculated by the schedulers, usually
+ because the instruction is too expensive to get this wrong. This hook
+ should return @code{false} if @var{insn} should not be speculated.
+@end deftypefn
+
@deftypefn {Target Hook} int TARGET_SCHED_SMS_RES_MII (struct ddg *@var{g})
This hook is called by the swing modulo scheduler to calculate a
resource-based lower bound which is based on the resources available in
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index ea74d37..756c118 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -4882,6 +4882,8 @@ them: try the first ones in this list first.
@hook TARGET_SCHED_SET_SCHED_FLAGS
+@hook TARGET_SCHED_CAN_SPECULATE_INSN
+
@hook TARGET_SCHED_SMS_RES_MII
@hook TARGET_SCHED_DISPATCH
diff --git a/gcc/sched-rgn.c b/gcc/sched-rgn.c
index 2af3a03..a09fc5d 100644
--- a/gcc/sched-rgn.c
+++ b/gcc/sched-rgn.c
@@ -2147,12 +2147,19 @@ static int
can_schedule_ready_p (rtx_insn *insn)
{
/* An interblock motion? */
- if (INSN_BB (insn) != target_bb
- && IS_SPECULATIVE_INSN (insn)
- && !check_live (insn, INSN_BB (insn)))
- return 0;
- else
- return 1;
+ if (INSN_BB (insn) != target_bb && IS_SPECULATIVE_INSN (insn))
+ {
+ /* Cannot schedule this insn unless all operands are live. */
+ if (!check_live (insn, INSN_BB (insn)))
+ return 0;
+
+ /* Should not move expensive instructions speculatively. */
+ if (GET_CODE (PATTERN (insn)) != CLOBBER
+ && !targetm.sched.can_speculate_insn (insn))
+ return 0;
+ }
+
+ return 1;
}
/* Updates counter and other information. Split from can_schedule_ready_p ()
diff --git a/gcc/target.def b/gcc/target.def
index 7308da1..dbb5d76 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -1480,6 +1480,13 @@ DEFHOOK_UNDOC
"Return speculation types that are checked for instruction @var{insn}",
unsigned int, (rtx_insn *insn), NULL)
+DEFHOOK
+(can_speculate_insn,
+ "Some instructions should never be speculated by the schedulers, usually\n\
+ because the instruction is too expensive to get this wrong. This hook\n\
+ should return @code{false} if @var{insn} should not be speculated.",
+ bool, (rtx_insn *insn), hook_bool_rtx_insn_true)
+
DEFHOOK_UNDOC
(skip_rtx_p,
"Return bool if rtx scanning should just skip current layer and\
--
1.9.3
