[m-rev.] diff: MR_succeed_discard
Zoltan Somogyi
zs at cs.mu.OZ.AU
Wed Oct 5 09:33:18 AEST 2005
Fix an optimization that tries to turn MR_succeed() into MR_succeed_discard(),
which throws away nondet stack frames at the last success of the relevant
procedure.
compiler/opt_util.m:
Fix the overly conservative approximation here that prevented
peephole.m from applying that optimization. It was considering
livevals() instructions as potentially affecting redoip slots,
which cannot be farther from the truth.
Change the relevant predicate from an if-then-else with a default
to a switch, to prevent similar problems in future.
compiler/peephole.m:
Don't apply the existing transformation pattern unless we find an
assertion that no other stack frame exists on top of the current one,
since it isn't valid then.
compiler/code_util.m:
Include that assertion in the comment of the instruction that assigns
to the redoip slot, which is where peephole.m looks for it.
We could store the assertion in an extra slot to assignment statements
in the LLDS, but that would require changes in lots of places and lead
to significant space overhead. This way is simpler, and has no overhead
to speak of. Any LLDS transformation that modifies the comment may
destroy the assertion, but the chance that it will incorrectly add or
even keep the assertion is about zero.
Zoltan.
cvs diff: Diffing .
cvs diff: Diffing analysis
cvs diff: Diffing bindist
cvs diff: Diffing boehm_gc
cvs diff: Diffing boehm_gc/Mac_files
cvs diff: Diffing boehm_gc/cord
cvs diff: Diffing boehm_gc/cord/private
cvs diff: Diffing boehm_gc/doc
cvs diff: Diffing boehm_gc/include
cvs diff: Diffing boehm_gc/include/private
cvs diff: Diffing boehm_gc/tests
cvs diff: Diffing browser
cvs diff: Diffing bytecode
cvs diff: Diffing compiler
Index: compiler/code_info.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/code_info.m,v
retrieving revision 1.306
diff -u -r1.306 code_info.m
--- compiler/code_info.m 30 Sep 2005 08:08:16 -0000 1.306
+++ compiler/code_info.m 4 Oct 2005 04:52:19 -0000
@@ -1527,9 +1527,10 @@
stack__top_det(ResumePoints, ResumePoint),
code_info__pick_stack_resume_point(ResumePoint, _, StackLabel),
LabelConst = const(code_addr_const(StackLabel)),
+ % peephole.m looks for the "curfr==maxfr" pattern in the comment.
Code = node([
assign(redoip(lval(curfr)), LabelConst)
- - "restore redoip for quarter disj hijack"
+ - "restore redoip for quarter disj hijack (curfr==maxfr)"
])
;
HijackInfo = disj_half_hijack(RedoipSlot),
@@ -1537,9 +1538,10 @@
"resume point known in disj_half_hijack"),
require(unify(CurfrMaxfr, must_be_equal),
"maxfr may differ from curfr in disj_half_hijack"),
+ % peephole.m looks for the "curfr==maxfr" pattern in the comment.
Code = node([
assign(redoip(lval(curfr)), lval(RedoipSlot))
- - "restore redoip for half disj hijack"
+ - "restore redoip for half disj hijack (curfr==maxfr)"
])
;
HijackInfo = disj_full_hijack(RedoipSlot, RedofrSlot),
Index: compiler/opt_util.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/opt_util.m,v
retrieving revision 1.135
diff -u -r1.135 opt_util.m
--- compiler/opt_util.m 14 Sep 2005 01:29:09 -0000 1.135
+++ compiler/opt_util.m 4 Oct 2005 01:15:45 -0000
@@ -567,9 +567,17 @@
:- pred straight_alternative_2(list(instruction)::in, list(instruction)::in,
list(instruction)::out, list(instruction)::out) is semidet.
-straight_alternative_2([Instr0 | Instrs0], Between0, Between, After) :-
+straight_alternative_2([Instr0 | Instrs0], !Between, After) :-
Instr0 = Uinstr0 - _,
(
+ Uinstr0 = label(_)
+ ->
+ fail
+ ;
+ Uinstr0 = goto(do_succeed(no))
+ ->
+ After = Instrs0
+ ;
(
can_instr_branch_away(Uinstr0, no),
touches_nondet_ctrl_instr(Uinstr0, no)
@@ -578,13 +586,8 @@
( CodeAddr = do_fail ; CodeAddr = do_redo )
)
->
- straight_alternative_2(Instrs0, [Instr0 | Between0],
- Between, After)
- ;
- Uinstr0 = goto(do_succeed(no))
- ->
- Between = Between0,
- After = Instrs0
+ !:Between = [Instr0 | !.Between],
+ straight_alternative_2(Instrs0, !Between, After)
;
fail
).
@@ -1485,35 +1488,72 @@
has_both_incr_decr_sp_2(Instrs, !HasIncr, !HasDecr).
touches_nondet_ctrl([], no).
-touches_nondet_ctrl([Uinstr - _ | Instrs], Touch) :-
- touches_nondet_ctrl_instr(Uinstr, Touch0),
+touches_nondet_ctrl([Uinstr - _ | Instrs], !:Touch) :-
+ touches_nondet_ctrl_instr(Uinstr, !:Touch),
(
- Touch0 = yes,
- Touch = yes
+ !.Touch = yes
;
- Touch0 = no,
- touches_nondet_ctrl(Instrs, Touch)
+ !.Touch = no,
+ touches_nondet_ctrl(Instrs, !:Touch)
).
:- pred touches_nondet_ctrl_instr(instr::in, bool::out) is det.
touches_nondet_ctrl_instr(Uinstr, Touch) :-
- ( Uinstr = assign(Lval, Rval) ->
+ (
+ ( Uinstr = comment(_)
+ ; Uinstr = livevals(_)
+ ; Uinstr = label(_)
+ ; Uinstr = free_heap(_)
+ ; Uinstr = store_ticket(_)
+ ; Uinstr = reset_ticket(_, _)
+ ; Uinstr = prune_ticket
+ ; Uinstr = discard_ticket
+ ; Uinstr = prune_tickets_to(_)
+ ; Uinstr = mark_ticket_stack(_)
+ ; Uinstr = incr_sp(_, _)
+ ; Uinstr = decr_sp(_)
+ ; Uinstr = decr_sp_and_return(_)
+ ),
+ Touch = no
+ ;
+ ( Uinstr = mkframe(_, _)
+ ; Uinstr = goto(_)
+ ; Uinstr = computed_goto(_, _)
+ ; Uinstr = call(_, _, _, _, _, _) % This is a safe approximation.
+ ; Uinstr = if_val(_, _)
+ ; Uinstr = c_code(_, _)
+ ; Uinstr = save_maxfr(_)
+ ; Uinstr = restore_maxfr(_)
+ ; Uinstr = init_sync_term(_, _) % This is a safe approximation.
+ ; Uinstr = fork(_, _, _) % This is a safe approximation.
+ ; Uinstr = join_and_terminate(_) % This is a safe approximation.
+ ; Uinstr = join_and_continue(_, _) % This is a safe approximation.
+ ),
+ Touch = yes
+ ;
+ Uinstr = block(_, _, _),
+ % Blocks aren't introduced until after the last user of this predicate.
+ unexpected(this_file, "touches_nondet_ctrl_instr: block")
+ ;
+ Uinstr = assign(Lval, Rval),
touches_nondet_ctrl_lval(Lval, TouchLval),
touches_nondet_ctrl_rval(Rval, TouchRval),
bool__or(TouchLval, TouchRval, Touch)
- ; Uinstr = incr_hp(Lval, _, _, Rval, _) ->
+ ;
+ Uinstr = incr_hp(Lval, _, _, Rval, _),
touches_nondet_ctrl_lval(Lval, TouchLval),
touches_nondet_ctrl_rval(Rval, TouchRval),
bool__or(TouchLval, TouchRval, Touch)
- ; Uinstr = mark_hp(Lval) ->
+ ;
+ Uinstr = mark_hp(Lval),
touches_nondet_ctrl_lval(Lval, Touch)
- ; Uinstr = restore_hp(Rval) ->
+ ;
+ Uinstr = restore_hp(Rval),
touches_nondet_ctrl_rval(Rval, Touch)
- ; Uinstr = pragma_c(_, Components, _, _, _, _, _, _, _) ->
- touches_nondet_ctrl_components(Components, Touch)
;
- Touch = yes
+ Uinstr = pragma_c(_, Components, _, _, _, _, _, _, _),
+ touches_nondet_ctrl_components(Components, Touch)
).
:- pred touches_nondet_ctrl_lval(lval::in, bool::out) is det.
Index: compiler/peephole.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/peephole.m,v
retrieving revision 1.85
diff -u -r1.85 peephole.m
--- compiler/peephole.m 14 Sep 2005 01:29:10 -0000 1.85
+++ compiler/peephole.m 4 Oct 2005 04:55:00 -0000
@@ -344,7 +344,8 @@
Base = curfr,
Redoip = const(code_addr_const(do_fail)),
opt_util__straight_alternative(Instrs0, Between, After),
- opt_util__touches_nondet_ctrl(Between, no)
+ opt_util__touches_nondet_ctrl(Between, no),
+ string__sub_string_search(Comment, "curfr==maxfr", _)
->
list__condense([Between,
[goto(do_succeed(yes)) - "early discard"], After], Instrs)
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