Scheduler fixes (PR17808)
Steven Bosscher
stevenb@suse.de
Sun Jul 3 15:16:00 GMT 2005
Hi,
This patch is Maxim Kuvyrkov's fix for the interblock scheduling
dependencies problem, and my fix for the intra-block case.
For the interblock problem , sched-deps should not clear the
reg_pending_* lists when facing a conditional jump. Without the
patch, the scheduler would produce wrong code.
In the intra-block case, the patch makes sched-rgn add dependencies
on all cond_exec insns to jumps at the end of (single-block) regions,
so that the cond_exec insns are scheduled before the jump even if
sched_get_condition says that the insn are not dependent. Without
the patch, the jump ends up in the middle of the basic block, and we
get an ICE. I have not tested this part of the patch yet because I
don't know how to test a cross to ARM (or another cond_exec target
that uses sched-rgn after reload).
I have bootstrapped and tested this patch on i686 and ia64, once with
an otherwise unpatched mainline, and once with an extra patch to set
flag_rename_registers at -O2 and higher. There are two new failures
on ia64, because of assembler warnings:
/tmp/ccBDW5xy.s: Assembler messages:
/tmp/ccBDW5xy.s:186: Warning: Additional NOP may be necessary to workaround Itanium processor A/B step errata
I am not sure what to do about this.
Richard E., could you see if this patch works for you on ARM?
Gr.
Steven
* sched-deps.c (sched_get_condition): Enable #if 0'ed code.
(sched_insns_conditions_mutex_p): Split out from...
(add_dependence): ...here. But don't call it from here.
(add_dependence_list): Check sched_insns_conditions_mutex_p
before calling add_dependence.
(add_dependence_list_and_free): Likewise.
(fixup_sched_groups): Likewise.
(sched_analyze_1): Likewise.
(sched_analyze_2): Likewise (and replace a "0" with REG_DEP_TRUE).
(sched_analyze): Likewise.
(sched_analyze_insn): Likewise.
* sched-ebb.c (add_deps_for_risky_insns): Likewise.
* sched-rgn.c (add_branch_dependences): Likewise. Also, add
dependencies on all COND_EXEC insns to jumps ending basic blocks
when doing intrablock scheduling.
* sched-int.h (sched_insns_conditions_mutex_p): Add prototype.
Index: sched-deps.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/sched-deps.c,v
retrieving revision 1.93
diff -u -3 -p -r1.93 sched-deps.c
--- sched-deps.c 25 Jun 2005 02:01:03 -0000 1.93
+++ sched-deps.c 3 Jul 2005 13:46:18 -0000
@@ -149,11 +149,7 @@ sched_get_condition (rtx insn)
return 0;
src = SET_SRC (pc_set (insn));
-#if 0
- /* The previous code here was completely invalid and could never extract
- the condition from a jump. This code does the correct thing, but that
- triggers latent bugs later in the scheduler on ports with conditional
- execution. So this is disabled for now. */
+
if (XEXP (src, 2) == pc_rtx)
return XEXP (src, 0);
else if (XEXP (src, 1) == pc_rtx)
@@ -166,11 +162,11 @@ sched_get_condition (rtx insn)
return gen_rtx_fmt_ee (revcode, GET_MODE (cond), XEXP (cond, 0),
XEXP (cond, 1));
}
-#endif
return 0;
}
+
/* Return nonzero if conditions COND1 and COND2 can never be both true. */
static int
@@ -184,6 +180,32 @@ conditions_mutex_p (rtx cond1, rtx cond2
return 1;
return 0;
}
+
+/* Return true if insn1 and insn2 can never depend on one another because
+ the conditions under which they are executed are mutually exclusive. */
+bool
+sched_insns_conditions_mutex_p (rtx insn1, rtx insn2)
+{
+ rtx cond1, cond2;
+
+ /* flow.c doesn't handle conditional lifetimes entirely correctly;
+ calls mess up the conditional lifetimes. */
+ if (!CALL_P (insn1) && !CALL_P (insn2))
+ {
+ cond1 = sched_get_condition (insn1);
+ cond2 = sched_get_condition (insn2);
+ if (cond1 && cond2
+ && conditions_mutex_p (cond1, cond2)
+ /* Make sure first instruction doesn't affect condition of second
+ instruction if switched. */
+ && !modified_in_p (cond1, insn2)
+ /* Make sure second instruction doesn't affect condition of first
+ instruction if switched. */
+ && !modified_in_p (cond2, insn1))
+ return true;
+ }
+ return false;
+}
/* Add ELEM wrapped in an INSN_LIST with reg note kind DEP_TYPE to the
LOG_LINKS of INSN, if not already there. DEP_TYPE indicates the
@@ -195,7 +217,6 @@ add_dependence (rtx insn, rtx elem, enum
{
rtx link;
int present_p;
- rtx cond1, cond2;
/* Don't depend an insn on itself. */
if (insn == elem)
@@ -207,26 +228,6 @@ add_dependence (rtx insn, rtx elem, enum
if (NOTE_P (elem))
return 0;
- /* flow.c doesn't handle conditional lifetimes entirely correctly;
- calls mess up the conditional lifetimes. */
- /* ??? add_dependence is the wrong place to be eliding dependencies,
- as that forgets that the condition expressions themselves may
- be dependent. */
- if (!CALL_P (insn) && !CALL_P (elem))
- {
- cond1 = sched_get_condition (insn);
- cond2 = sched_get_condition (elem);
- if (cond1 && cond2
- && conditions_mutex_p (cond1, cond2)
- /* Make sure first instruction doesn't affect condition of second
- instruction if switched. */
- && !modified_in_p (cond1, elem)
- /* Make sure second instruction doesn't affect condition of first
- instruction if switched. */
- && !modified_in_p (cond2, insn))
- return 0;
- }
-
present_p = 1;
#ifdef INSN_SCHEDULING
/* ??? No good way to tell from here whether we're doing interblock
@@ -348,7 +349,10 @@ static void
add_dependence_list (rtx insn, rtx list, enum reg_note dep_type)
{
for (; list; list = XEXP (list, 1))
- add_dependence (insn, XEXP (list, 0), dep_type);
+ {
+ if (! sched_insns_conditions_mutex_p (insn, XEXP (list, 0)))
+ add_dependence (insn, XEXP (list, 0), dep_type);
+ }
}
/* Similar, but free *LISTP at the same time. */
@@ -360,7 +364,8 @@ add_dependence_list_and_free (rtx insn,
for (list = *listp, *listp = NULL; list ; list = next)
{
next = XEXP (list, 1);
- add_dependence (insn, XEXP (list, 0), dep_type);
+ if (! sched_insns_conditions_mutex_p (insn, XEXP (list, 0)))
+ add_dependence (insn, XEXP (list, 0), dep_type);
free_INSN_LIST_node (list);
}
}
@@ -393,7 +398,7 @@ delete_all_dependences (rtx insn)
static void
fixup_sched_groups (rtx insn)
{
- rtx link;
+ rtx link, prev_nonnote;
for (link = LOG_LINKS (insn); link ; link = XEXP (link, 1))
{
@@ -405,14 +410,17 @@ fixup_sched_groups (rtx insn)
if (XEXP (link, 0) == i)
goto next_link;
} while (SCHED_GROUP_P (i));
- add_dependence (i, XEXP (link, 0), REG_NOTE_KIND (link));
+ if (! sched_insns_conditions_mutex_p (i, XEXP (link, 0)))
+ add_dependence (i, XEXP (link, 0), REG_NOTE_KIND (link));
next_link:;
}
delete_all_dependences (insn);
- if (BLOCK_FOR_INSN (insn) == BLOCK_FOR_INSN (prev_nonnote_insn (insn)))
- add_dependence (insn, prev_nonnote_insn (insn), REG_DEP_ANTI);
+ prev_nonnote = prev_nonnote_insn (insn);
+ if (BLOCK_FOR_INSN (insn) == BLOCK_FOR_INSN (prev_nonnote)
+ && ! sched_insns_conditions_mutex_p (insn, prev_nonnote))
+ add_dependence (insn, prev_nonnote, REG_DEP_ANTI);
}
/* Process an insn's memory dependencies. There are four kinds of
@@ -620,7 +628,8 @@ sched_analyze_1 (struct deps *deps, rtx
pending_mem = deps->pending_read_mems;
while (pending)
{
- if (anti_dependence (XEXP (pending_mem, 0), t))
+ if (anti_dependence (XEXP (pending_mem, 0), t)
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
add_dependence (insn, XEXP (pending, 0), REG_DEP_ANTI);
pending = XEXP (pending, 1);
@@ -631,7 +640,8 @@ sched_analyze_1 (struct deps *deps, rtx
pending_mem = deps->pending_write_mems;
while (pending)
{
- if (output_dependence (XEXP (pending_mem, 0), t))
+ if (output_dependence (XEXP (pending_mem, 0), t)
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
pending = XEXP (pending, 1);
@@ -759,7 +769,8 @@ sched_analyze_2 (struct deps *deps, rtx
pending_mem = deps->pending_read_mems;
while (pending)
{
- if (read_dependence (XEXP (pending_mem, 0), t))
+ if (read_dependence (XEXP (pending_mem, 0), t)
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
add_dependence (insn, XEXP (pending, 0), REG_DEP_ANTI);
pending = XEXP (pending, 1);
@@ -771,16 +782,17 @@ sched_analyze_2 (struct deps *deps, rtx
while (pending)
{
if (true_dependence (XEXP (pending_mem, 0), VOIDmode,
- t, rtx_varies_p))
- add_dependence (insn, XEXP (pending, 0), 0);
+ t, rtx_varies_p)
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
+ add_dependence (insn, XEXP (pending, 0), REG_DEP_TRUE);
pending = XEXP (pending, 1);
pending_mem = XEXP (pending_mem, 1);
}
for (u = deps->last_pending_memory_flush; u; u = XEXP (u, 1))
- if (!JUMP_P (XEXP (u, 0))
- || deps_may_trap_p (x))
+ if ((! JUMP_P (XEXP (u, 0)) || deps_may_trap_p (x))
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (u, 0)))
add_dependence (insn, XEXP (u, 0), REG_DEP_ANTI);
/* Always add these dependencies to pending_reads, since
@@ -966,7 +978,8 @@ sched_analyze_insn (struct deps *deps, r
pending_mem = deps->pending_write_mems;
while (pending)
{
- add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
+ if (! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
+ add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
pending = XEXP (pending, 1);
pending_mem = XEXP (pending_mem, 1);
}
@@ -975,7 +988,8 @@ sched_analyze_insn (struct deps *deps, r
pending_mem = deps->pending_read_mems;
while (pending)
{
- if (MEM_VOLATILE_P (XEXP (pending_mem, 0)))
+ if (MEM_VOLATILE_P (XEXP (pending_mem, 0))
+ && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
pending = XEXP (pending, 1);
pending_mem = XEXP (pending_mem, 1);
@@ -1019,7 +1033,7 @@ sched_analyze_insn (struct deps *deps, r
{
/* In the case of barrier the most added dependencies are not
real, so we use anti-dependence here. */
- if (GET_CODE (PATTERN (insn)) == COND_EXEC)
+ if (sched_get_condition (insn))
{
EXECUTE_IF_SET_IN_REG_SET (&deps->reg_last_in_use, 0, i, rsi)
{
@@ -1066,7 +1080,7 @@ sched_analyze_insn (struct deps *deps, r
{
/* If the current insn is conditional, we can't free any
of the lists. */
- if (GET_CODE (PATTERN (insn)) == COND_EXEC)
+ if (sched_get_condition (insn))
{
EXECUTE_IF_SET_IN_REG_SET (reg_pending_uses, 0, i, rsi)
{
Index: sched-ebb.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/sched-ebb.c,v
retrieving revision 1.44
diff -u -3 -p -r1.44 sched-ebb.c
--- sched-ebb.c 25 Jun 2005 02:01:03 -0000 1.44
+++ sched-ebb.c 3 Jul 2005 13:46:18 -0000
@@ -454,7 +454,8 @@ add_deps_for_risky_insns (rtx head, rtx
/* We can not change the mode of the backward
dependency because REG_DEP_ANTI has the lowest
rank. */
- if (add_dependence (insn, prev, REG_DEP_ANTI))
+ if (! sched_insns_conditions_mutex_p (insn, prev)
+ && add_dependence (insn, prev, REG_DEP_ANTI))
add_forward_dependence (prev, insn, REG_DEP_ANTI);
break;
Index: sched-int.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/sched-int.h,v
retrieving revision 1.38
diff -u -3 -p -r1.38 sched-int.h
--- sched-int.h 25 Jun 2005 02:01:03 -0000 1.38
+++ sched-int.h 3 Jul 2005 13:46:18 -0000
@@ -331,6 +331,7 @@ enum INSN_TRAP_CLASS
extern void print_insn (char *, rtx, int);
/* Functions in sched-deps.c. */
+extern bool sched_insns_conditions_mutex_p (rtx, rtx);
extern int add_dependence (rtx, rtx, enum reg_note);
extern void sched_analyze (struct deps *, rtx, rtx);
extern void init_deps (struct deps *);
Index: sched-rgn.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/sched-rgn.c,v
retrieving revision 1.96
diff -u -3 -p -r1.96 sched-rgn.c
--- sched-rgn.c 25 Jun 2005 02:01:03 -0000 1.96
+++ sched-rgn.c 3 Jul 2005 13:46:18 -0000
@@ -1881,6 +1881,8 @@ add_branch_dependences (rtx head, rtx ta
cc0 setters remain at the end because they can't be moved away from
their cc0 user.
+ COND_EXEC insns cannot be moved past a branch (see e.g. PR17808).
+
Insns setting CLASS_LIKELY_SPILLED_P registers (usually return values)
are not moved before reload because we can wind up with register
allocation failures. */
@@ -1904,7 +1906,8 @@ add_branch_dependences (rtx head, rtx ta
{
if (last != 0 && !find_insn_list (insn, LOG_LINKS (last)))
{
- add_dependence (last, insn, REG_DEP_ANTI);
+ if (! sched_insns_conditions_mutex_p (last, insn))
+ add_dependence (last, insn, REG_DEP_ANTI);
INSN_REF_COUNT (insn)++;
}
@@ -1930,9 +1933,61 @@ add_branch_dependences (rtx head, rtx ta
if (INSN_REF_COUNT (insn) != 0)
continue;
- add_dependence (last, insn, REG_DEP_ANTI);
+ if (! sched_insns_conditions_mutex_p (last, insn))
+ add_dependence (last, insn, REG_DEP_ANTI);
INSN_REF_COUNT (insn) = 1;
}
+
+#ifdef HAVE_conditional_execution
+ /* Finally, if the block ends in a jump, and we are doing intra-block
+ scheduling, make sure that the branch depends on any COND_EXEC insns
+ inside the block to avoid moving the COND_EXECs past the branch insn.
+
+ We only have to do this after reload, because (1) before reload there
+ are no COND_EXEC insns, and (2) the region scheduler is an intra-block
+ scheduler after reload.
+
+ FIXME: We could in some cases move COND_EXEC insns past the branch if
+ this scheduler would be a little smarter. Consider this code:
+
+ T = [addr]
+ C ? addr += 4
+ C ? X += 12
+ C ? T += 1
+ !C ? jump foo
+
+ On a target with a one cycle stall on a memory access the optimal
+ sequence would be:
+
+ T = [addr]
+ C ? addr += 4
+ C ? T += 1
+ C ? jump foo
+ !C ? X += 12
+
+ We don't want to put the 'X += 12' before the branch because it just
+ wastes a cycle of execution time when the branch is taken.
+
+ Note that in the example "!C" will always be true. That is another
+ possible improvement for handling COND_EXECs in this scheduler: it
+ could remove always-true predicates. */
+
+ if (!reload_completed || ! JUMP_P (tail))
+ return;
+
+ insn = PREV_INSN (tail);
+ while (insn != head)
+ {
+ /* Note that we want to add this dependency even when
+ sched_insns_conditions_mutex_p returns true. The whole point
+ is that we _want_ this dependency, even if these insns really
+ are independent. */
+ if (INSN_P (insn) && GET_CODE (PATTERN (insn)) == COND_EXEC)
+ add_dependence (tail, insn, REG_DEP_ANTI);
+
+ insn = PREV_INSN (insn);
+ }
+#endif
}
/* Data structures for the computation of data dependences in a regions. We
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