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672f77c4ecd07daaf01217bc81c336dcf5d6aa02
mercury/compiler/code_util.m
Zoltan Somogyi 672f77c4ec Add a new compiler option. --inform-ite-instead-of-switch. 
Estimated hours taken: 20
Branches: main

Add a new compiler option. --inform-ite-instead-of-switch. If this is enabled,
the compiler will generate informational messages about if-then-elses that
it thinks should be converted to switches for the sake of program reliability.

Act on the output generated by this option.

compiler/simplify.m:
	Implement the new option.

	Fix an old bug that could cause us to generate warnings about code
	that was OK in one duplicated copy but not in another (where a switch
	arm's code is duplicated due to the case being selected for more than
	one cons_id).

compiler/options.m:
	Add the new option.

	Add a way to test for the bug fix in simplify.

doc/user_guide.texi:
	Document the new option.

NEWS:
	Mention the new option.

library/*.m:
mdbcomp/*.m:
browser/*.m:
compiler/*.m:
deep_profiler/*.m:
	Convert if-then-elses to switches at most of the sites suggested by the
	new option. At the remaining sites, switching to switches would have
	nontrivial downsides. This typically happens with the switched-on type
	has many functors, and we treat one or two specially (e.g. cons/2 in
	the cons_id type).

	Perform misc cleanups in the vicinity of the if-then-else to switch
	conversions.

	In a few cases, improve the error messages generated.

compiler/accumulator.m:
compiler/hlds_goal.m:
	(Rename and) move insts for particular kinds of goal from
	accumulator.m to hlds_goal.m, to allow them to be used in other
	modules. Using these insts allowed us to eliminate some if-then-elses
	entirely.

compiler/exprn_aux.m:
	Instead of fixing some if-then-elses, delete the predicates containing
	them, since they aren't used, and (as pointed out by the new option)
	would need considerable other fixing if they were ever needed again.

compiler/lp_rational.m:
	Add prefixes to the names of the function symbols on some types,
	since without those prefixes, it was hard to figure out what type
	the switch corresponding to an old if-then-else was switching on.

tests/invalid/reserve_tag.err_exp:
	Expect a new, improved error message.
2007-11-23 07:36:01 +00:00

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%-----------------------------------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%-----------------------------------------------------------------------------%
% Copyright (C) 1994-2007 The University of Melbourne.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%-----------------------------------------------------------------------------%
%
% File: code_util.m.
%
% Various utilities routines for code generation and recognition of builtins.
%
%-----------------------------------------------------------------------------%
:- module ll_backend.code_util.
:- interface.
:- import_module hlds.hlds_goal.
:- import_module hlds.hlds_llds.
:- import_module hlds.hlds_module.
:- import_module hlds.hlds_pred.
:- import_module hlds.hlds_rtti.
:- import_module ll_backend.llds.
:- import_module mdbcomp.prim_data.
:- import_module parse_tree.prog_data.
:- import_module assoc_list.
:- import_module bool.
:- import_module list.
:- import_module maybe.
:- import_module pair.
%-----------------------------------------------------------------------------%
% Create a code address which holds the address of the specified procedure.
% The `immed' argument should be `no' if the the caller wants the returned
% address to be valid from everywhere in the program. If being valid from
% within the current procedure is enough, this argument should be `yes'
% wrapped around the value of the --procs-per-c-function option and the
% current procedure id. Using an address that is only valid from within
% the current procedure may make jumps more efficient.
%
:- type immed == maybe(pair(int, pred_proc_id)).
:- func make_entry_label(module_info, pred_id, proc_id, immed) = code_addr.
:- func make_entry_label_from_rtti(rtti_proc_label, immed) = code_addr.
% Create a label which holds the address of the specified procedure,
% which must be defined in the current module (procedures that are
% imported from other modules have representations only as code_addrs,
% not as labels, since their address is not known at C compilation time).
% The fourth argument has the same meaning as for make_entry_label.
%
:- func make_local_entry_label(module_info, pred_id, proc_id, immed) = label.
% Create a label internal to a Mercury procedure.
%
:- func make_internal_label(module_info, pred_id, proc_id, int) = label.
:- func extract_proc_label_from_code_addr(code_addr) = proc_label.
:- pred arg_loc_to_register(arg_loc::in, lval::out) is det.
:- pred max_mentioned_reg(list(lval)::in, int::out) is det.
:- pred max_mentioned_abs_reg(list(abs_locn)::in, int::out) is det.
:- pred goal_may_alloc_temp_frame(hlds_goal::in, bool::out) is det.
% Negate a condition.
% This is used mostly just to make the generated code more readable.
%
:- pred neg_rval(rval::in, rval::out) is det.
:- pred negate_the_test(list(instruction)::in, list(instruction)::out) is det.
% These predicates return the set of lvals referenced in an rval
% and an lval respectively. Lvals referenced indirectly through
% lvals of the form var(_) are not counted.
%
:- pred lvals_in_rval(rval::in, list(lval)::out) is det.
:- pred lvals_in_lval(lval::in, list(lval)::out) is det.
:- pred lvals_in_lvals(list(lval)::in, list(lval)::out) is det.
% Given a procedure that already has its arg_info field filled in,
% return a list giving its input variables and their initial locations.
%
:- pred build_input_arg_list(proc_info::in, assoc_list(prog_var, lval)::out)
is det.
%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
:- implementation.
:- import_module backend_libs.builtin_ops.
:- import_module backend_libs.proc_label.
:- import_module backend_libs.rtti.
:- import_module hlds.code_model.
:- import_module libs.compiler_util.
:- import_module int.
:- import_module term.
%---------------------------------------------------------------------------%
make_entry_label(ModuleInfo, PredId, ProcId, Immed) = ProcAddr :-
RttiProcLabel = make_rtti_proc_label(ModuleInfo, PredId, ProcId),
ProcAddr = make_entry_label_from_rtti(RttiProcLabel, Immed).
make_entry_label_from_rtti(RttiProcLabel, Immed) = ProcAddr :-
( RttiProcLabel ^ proc_is_imported = yes ->
ProcLabel = make_proc_label_from_rtti(RttiProcLabel),
ProcAddr = code_imported_proc(ProcLabel)
;
Label = make_local_entry_label_from_rtti(RttiProcLabel, Immed),
ProcAddr = code_label(Label)
).
make_local_entry_label(ModuleInfo, PredId, ProcId, Immed) = Label :-
RttiProcLabel = make_rtti_proc_label(ModuleInfo, PredId, ProcId),
Label = make_local_entry_label_from_rtti(RttiProcLabel, Immed).
:- func make_local_entry_label_from_rtti(rtti_proc_label, immed) = label.
make_local_entry_label_from_rtti(RttiProcLabel, Immed) = Label :-
ProcLabel = make_proc_label_from_rtti(RttiProcLabel),
(
Immed = no,
% If we want to define the label or use it to put it into a data
% structure, a label that is usable only within the current C module
% won't do.
( RttiProcLabel ^ proc_is_exported = yes ->
EntryType = entry_label_exported
;
EntryType = entry_label_local
),
Label = entry_label(EntryType, ProcLabel)
;
Immed = yes(ProcsPerFunc - proc(CurPredId, CurProcId)),
Label = choose_local_label_type(ProcsPerFunc, CurPredId, CurProcId,
RttiProcLabel ^ pred_id, RttiProcLabel ^ proc_id, ProcLabel)
).
:- func choose_local_label_type(int, pred_id, proc_id, pred_id, proc_id,
proc_label) = label.
choose_local_label_type(ProcsPerFunc, CurPredId, CurProcId,
PredId, ProcId, ProcLabel) = Label :-
(
% If we want to branch to the label now, we prefer a form that is
% usable only within the current C module, since it is likely to be
% faster.
(
ProcsPerFunc = 0
;
PredId = CurPredId,
ProcId = CurProcId
)
->
EntryType = entry_label_c_local
;
EntryType = entry_label_local
),
Label = entry_label(EntryType, ProcLabel).
%-----------------------------------------------------------------------------%
make_internal_label(ModuleInfo, PredId, ProcId, LabelNum) = Label :-
ProcLabel = make_proc_label(ModuleInfo, PredId, ProcId),
Label = internal_label(LabelNum, ProcLabel).
extract_proc_label_from_code_addr(CodeAddr) = ProcLabel :-
( CodeAddr = code_label(Label) ->
ProcLabel = get_proc_label(Label)
; CodeAddr = code_imported_proc(ProcLabelPrime) ->
ProcLabel = ProcLabelPrime
;
unexpected(this_file, "extract_label_from_code_addr failed")
).
%-----------------------------------------------------------------------------%
arg_loc_to_register(ArgLoc, reg(reg_r, ArgLoc)).
%-----------------------------------------------------------------------------%
max_mentioned_reg(Lvals, MaxRegNum) :-
max_mentioned_reg_2(Lvals, 0, MaxRegNum).
:- pred max_mentioned_reg_2(list(lval)::in, int::in, int::out) is det.
max_mentioned_reg_2([], !MaxRegNum).
max_mentioned_reg_2([Lval | Lvals], !MaxRegNum) :-
( Lval = reg(reg_r, N) ->
int.max(N, !MaxRegNum)
;
true
),
max_mentioned_reg_2(Lvals, !MaxRegNum).
max_mentioned_abs_reg(Lvals, MaxRegNum) :-
max_mentioned_abs_reg_2(Lvals, 0, MaxRegNum).
:- pred max_mentioned_abs_reg_2(list(abs_locn)::in, int::in, int::out) is det.
max_mentioned_abs_reg_2([], !MaxRegNum).
max_mentioned_abs_reg_2([Lval | Lvals], !MaxRegNum) :-
( Lval = abs_reg(N) ->
int.max(N, !MaxRegNum)
;
true
),
max_mentioned_abs_reg_2(Lvals, !MaxRegNum).
%-----------------------------------------------------------------------------%
goal_may_alloc_temp_frame(hlds_goal(GoalExpr, _GoalInfo), May) :-
goal_may_alloc_temp_frame_2(GoalExpr, May).
:- pred goal_may_alloc_temp_frame_2(hlds_goal_expr::in, bool::out)
is det.
goal_may_alloc_temp_frame_2(generic_call(_, _, _, _), no).
goal_may_alloc_temp_frame_2(plain_call(_, _, _, _, _, _), no).
goal_may_alloc_temp_frame_2(unify(_, _, _, _, _), no).
% We cannot safely say that a foreign code fragment does not allocate
% temporary nondet frames without knowing all the #defined macros
% that expand to mktempframe and variants thereof. The performance
% impact of being too conservative is probably not too bad.
goal_may_alloc_temp_frame_2(call_foreign_proc(_, _, _, _, _, _, _), yes).
goal_may_alloc_temp_frame_2(scope(_, Goal), May) :-
Goal = hlds_goal(_, GoalInfo),
CodeModel = goal_info_get_code_model(GoalInfo),
(
CodeModel = model_non,
May = yes
;
( CodeModel = model_det
; CodeModel = model_semi
),
goal_may_alloc_temp_frame(Goal, May)
).
goal_may_alloc_temp_frame_2(negation(Goal), May) :-
goal_may_alloc_temp_frame(Goal, May).
goal_may_alloc_temp_frame_2(conj(_ConjType, Goals), May) :-
goal_list_may_alloc_temp_frame(Goals, May).
goal_may_alloc_temp_frame_2(disj(Goals), May) :-
goal_list_may_alloc_temp_frame(Goals, May).
goal_may_alloc_temp_frame_2(switch(_Var, _Det, Cases), May) :-
cases_may_alloc_temp_frame(Cases, May).
goal_may_alloc_temp_frame_2(if_then_else(_Vars, C, T, E), May) :-
( goal_may_alloc_temp_frame(C, yes) ->
May = yes
; goal_may_alloc_temp_frame(T, yes) ->
May = yes
;
goal_may_alloc_temp_frame(E, May)
).
goal_may_alloc_temp_frame_2(shorthand(ShorthandGoal), May) :-
goal_may_alloc_temp_frame_2_shorthand(ShorthandGoal,May).
:- pred goal_may_alloc_temp_frame_2_shorthand(shorthand_goal_expr::in,
bool::out) is det.
goal_may_alloc_temp_frame_2_shorthand(bi_implication(G1, G2), May) :-
( goal_may_alloc_temp_frame(G1, yes) ->
May = yes
;
goal_may_alloc_temp_frame(G2, May)
).
:- pred goal_list_may_alloc_temp_frame(list(hlds_goal)::in, bool::out) is det.
goal_list_may_alloc_temp_frame([], no).
goal_list_may_alloc_temp_frame([Goal | Goals], May) :-
( goal_may_alloc_temp_frame(Goal, yes) ->
May = yes
;
goal_list_may_alloc_temp_frame(Goals, May)
).
:- pred cases_may_alloc_temp_frame(list(case)::in, bool::out) is det.
cases_may_alloc_temp_frame([], no).
cases_may_alloc_temp_frame([case(_, Goal) | Cases], May) :-
( goal_may_alloc_temp_frame(Goal, yes) ->
May = yes
;
cases_may_alloc_temp_frame(Cases, May)
).
%-----------------------------------------------------------------------------%
neg_rval(Rval, NegRval) :-
( neg_rval_2(Rval, NegRval0) ->
NegRval = NegRval0
;
NegRval = unop(logical_not, Rval)
).
:- pred neg_rval_2(rval::in, rval::out) is semidet.
neg_rval_2(const(Const), const(NegConst)) :-
(
Const = llconst_true,
NegConst = llconst_false
;
Const = llconst_false,
NegConst = llconst_true
).
neg_rval_2(unop(logical_not, Rval), Rval).
neg_rval_2(binop(Op, X, Y), binop(NegOp, X, Y)) :-
neg_op(Op, NegOp).
:- pred neg_op(binary_op::in, binary_op::out) is semidet.
neg_op(eq, ne).
neg_op(ne, eq).
neg_op(int_lt, int_ge).
neg_op(int_le, int_gt).
neg_op(int_gt, int_le).
neg_op(int_ge, int_lt).
neg_op(str_eq, str_ne).
neg_op(str_ne, str_eq).
neg_op(str_lt, str_ge).
neg_op(str_le, str_gt).
neg_op(str_gt, str_le).
neg_op(str_ge, str_lt).
neg_op(float_eq, float_ne).
neg_op(float_ne, float_eq).
neg_op(float_lt, float_ge).
neg_op(float_le, float_gt).
neg_op(float_gt, float_le).
neg_op(float_ge, float_lt).
negate_the_test([], _) :-
unexpected(this_file, "negate_the_test on empty list").
negate_the_test([Instr0 | Instrs0], Instrs) :-
( Instr0 = llds_instr(if_val(Test, Target), Comment) ->
neg_rval(Test, NewTest),
Instrs = [llds_instr(if_val(NewTest, Target), Comment)]
;
negate_the_test(Instrs0, Instrs1),
Instrs = [Instr0 | Instrs1]
).
%-----------------------------------------------------------------------------%
lvals_in_lvals([], []).
lvals_in_lvals([First | Rest], FirstLvals ++ RestLvals) :-
lvals_in_lval(First, FirstLvals),
lvals_in_lvals(Rest, RestLvals).
lvals_in_rval(lval(Lval), [Lval | Lvals]) :-
lvals_in_lval(Lval, Lvals).
lvals_in_rval(var(_), []).
lvals_in_rval(mkword(_, Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_rval(const(_), []).
lvals_in_rval(unop(_, Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_rval(binop(_, Rval1, Rval2), Lvals1 ++ Lvals2) :-
lvals_in_rval(Rval1, Lvals1),
lvals_in_rval(Rval2, Lvals2).
lvals_in_rval(mem_addr(MemRef), Lvals) :-
lvals_in_mem_ref(MemRef, Lvals).
lvals_in_lval(reg(_, _), []).
lvals_in_lval(stackvar(_), []).
lvals_in_lval(parent_stackvar(_), []).
lvals_in_lval(framevar(_), []).
lvals_in_lval(succip, []).
lvals_in_lval(maxfr, []).
lvals_in_lval(curfr, []).
lvals_in_lval(succip_slot(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(redofr_slot(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(redoip_slot(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(succfr_slot(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(prevfr_slot(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(hp, []).
lvals_in_lval(sp, []).
lvals_in_lval(parent_sp, []).
lvals_in_lval(field(_, Rval1, Rval2), Lvals1 ++ Lvals2) :-
lvals_in_rval(Rval1, Lvals1),
lvals_in_rval(Rval2, Lvals2).
lvals_in_lval(lvar(_), []).
lvals_in_lval(temp(_, _), []).
lvals_in_lval(mem_ref(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_lval(global_var_ref(_), []).
:- pred lvals_in_mem_ref(mem_ref::in, list(lval)::out) is det.
lvals_in_mem_ref(stackvar_ref(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_mem_ref(framevar_ref(Rval), Lvals) :-
lvals_in_rval(Rval, Lvals).
lvals_in_mem_ref(heap_ref(Rval1, _, Rval2), Lvals1 ++ Lvals2) :-
lvals_in_rval(Rval1, Lvals1),
lvals_in_rval(Rval2, Lvals2).
%-----------------------------------------------------------------------------%
build_input_arg_list(ProcInfo, VarLvals) :-
proc_info_get_headvars(ProcInfo, HeadVars),
proc_info_arg_info(ProcInfo, ArgInfos),
assoc_list.from_corresponding_lists(HeadVars, ArgInfos, VarArgInfos),
build_input_arg_list_2(VarArgInfos, VarLvals).
:- pred build_input_arg_list_2(assoc_list(prog_var, arg_info)::in,
assoc_list(prog_var, lval)::out) is det.
build_input_arg_list_2([], []).
build_input_arg_list_2([V - Arg | Rest0], VarArgs) :-
Arg = arg_info(Loc, Mode),
(
Mode = top_in,
arg_loc_to_register(Loc, Reg),
VarArgs = [V - Reg | VarArgs0]
;
( Mode = top_out
; Mode = top_unused
),
VarArgs = VarArgs0
),
build_input_arg_list_2(Rest0, VarArgs0).
%---------------------------------------------------------------------------%
:- func this_file = string.
this_file = "code_util.m".
%-----------------------------------------------------------------------------%
:- end_module code_util.
%-----------------------------------------------------------------------------%
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