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mercury/compiler/stack_alloc.m
Zoltan Somogyi 62ec97d443 Report imports shadowed by other imports. 
If a module has two or more import_module or use_module declarations
for the same module, (typically, but not always, one being in its interface
and one in its implementation), generate an informational message about
each redundant declaration if --warn-unused-imports is enabled.

compiler/hlds_module.m:
    We used to record the set of imported/used modules, and the set of
    modules imported/used in the interface of the current module. However,
    these sets

    - did not record the distinction between imports and uses;
    - did not allow distinction between single and multiple imports/uses;
    - did not record the locations of the imports/uses.

    The first distinction was needed only by module_qual.m, which *did*
    pay attention to it; the other two were not needed at all.

    To generate messages for imports/uses shadowing other imports/uses,
    we need all three, so change the data structure storing such information
    for *direct* imports to one that records all three of the above kinds
    of information. (For imports made by read-in interface and optimization
    files, the old set of modules approach is fine, and this diff leaves
    the set of thus *indirectly* imported module names alone.)

compiler/unused_imports.m:
    Use the extra information now available to generate a
    severity_informational message about any import or use that is made
    redundant by an earlier, more general import or use.

    Fix two bugs in the code that generated warnings for just plain unused
    modules.

    (1) It did not consider that a use of the builtin type char justified
    an import of char.m, but without that import, the type is not visible.

    (2) It scanned cons_ids in goals in procedure bodies, but did not scan
    cons_ids that have been put into the const_struct_db. (I did not update
    the code here when I added the const_struct_db.)

    Also, add a (hopefully temporary) workaround for a bug in
    make_hlds_passes.m, which is noted below.

    However, there are at least three problems that prevent us from enabling
    --warn-unused-imports by default.

    (1) In some places, the import of a module is used only by clauses for
    a predicate that also has foreign procs. When compiled in a grade that
    selects one of those foreign_procs as the implementation of the predicate,
    the clauses are discarded *without* being added to the HLDS at all.
    This leads unused_imports.m to generate an uncalled-for warning in such
    cases. To fix this, we would need to preserve the Mercury clauses for
    *all* predicates, even those with foreign procs, and do all the semantic
    checks on them before throwing them away. (I tried to do this once, and
    failed, but the task should be easier after the item list change.)

    (2) We have two pieces of code to generate import warnings. The one in
    unused_imports.m operates on the HLDS after type and mode checking,
    while module_qual.m operates on the parse tree before the creation of
    the HLDS. The former is more powerful, since it knows e.g. what types and
    modes are used in the bodies of predicates, and hence can generate warnings
    about an import being unused *anywhere* in a module, as opposed to just
    unused in its interface.

    If --warn-unused-imports is enabled, we will get two separate set of
    reports about an interface import being unused in the interface,
    *unless* we get a type or mode error, in which case unused_imports.m
    won't be invoked. But in case we do get such errors, we don't want to
    throw away the warnings from module_qual.m. We could store them and
    throw them away only after we know we won't need them, or just get
    the two modules to generate identical error_specs for each warning,
    so that the sort_and_remove_dups of the error specs will do the
    throwing away for us for free, if we get that far.

    (3) The valid/bug100.m test case was added as a regression test for a bug
    that was fixed in module_qual.m. However the bug is still present in
    unused_imports.m.

compiler/make_hlds_passes.m:
    Give hlds_module.m the extra information it now needs for each item_avail.

    Add an XXX for a bug that cannot be fixed right now: the setting of
    the status of abstract instances to abstract_imported. (The "abstract"
    part is correct; the "imported" part may not be.)

compiler/intermod.m:
compiler/try_expand.m:
compiler/xml_documentation.m:
    Conform to the change in hlds_module.m.

compiler/module_qual.m:
    Update the documentation of the relationship of this module
    with unused_imports.m.

compiler/hlds_data.m:
    Document a problem with the status of instance definitions.

compiler/hlds_out_module.m:
    Update the code that prints out the module_info to conform to the change
    to hlds_module.m.

    Print status information about instances, which was needed to diagnose
    one of the bugs in unused_imports.m. Format the output for instances
    nicer.

compiler/prog_item.m:
    Add a convenience predicate.

compiler/prog_data.m:
    Remove a type synonym that makes things harder to understand, not easier.

compiler/modules.m:
    Delete an XXX that asks for the feature this diff implements.
    Add another XXX about how that feature could be improved.

compiler/Mercury.options.m:
    Add some more modules to the list of modules on which the compiler
    should be invoked with --no-warn-unused-imports.

compiler/*.m:
library/*.m:
mdbcomp/*.m:
browser/*.m:
deep_profiler/*.m:
mfilterjavac/*.m:
    Delete unneeded imports. Many of these shadow other imports, and some
    are just plain unneeded, as shown by --warn-unused-imports. In a few
    modules, there were a *lot* of unneeded imports, but most had just
    one or two.

    In a few cases, removing an import from a module, because it *itself*
    does not need it, required adding that same import to those of its
    submodules which *do* need it.

    In a few cases, conform to other changes above.

tests/invalid/Mercury.options:
    Test the generation of messages about import shadowing on the existing
    import_in_parent.m test case (although it was also tested very thoroughly
    when giving me the information needed for the deletion of all the
    unneeded imports above).

tests/*/*.{m,*exp}:
    Delete unneeded imports, and update any expected error messages
    to expect the now-smaller line numbers.
2015-08-25 00:38:49 +10:00

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%-----------------------------------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%-----------------------------------------------------------------------------%
% Copyright (C) 2002-2007, 2010-2012 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 stack_alloc.m.
% Authors: zs, conway.
%
% This module allocates stack slots to the variables that need to be saved
% across a call, across a goal that may fail, or in a parallel conjunction.
%
% The jobs is done in two steps. First we traverse the predicate definition
% looking for sets of variables that must be saved on the stack at the same
% time. If --optimize-stack-slots is set, then this phase is done by
% stack_opt.m; if --optimize-stack-slots is not set, then it is done by this
% module. Then we use a graph colouring algorithm to find an allocation of
% stack slots (colours) to variables such that in each set of variables that
% must be saved at the same time, each variable has a different colour.
%
%-----------------------------------------------------------------------------%
:- module ll_backend.stack_alloc.
:- interface.
:- import_module hlds.hlds_module.
:- import_module hlds.hlds_pred.
%-----------------------------------------------------------------------------%
:- pred allocate_stack_slots_in_proc(module_info::in, pred_proc_id::in,
proc_info::in, proc_info::out) is det.
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
:- implementation.
:- import_module check_hlds.type_util.
:- import_module hlds.code_model.
:- import_module hlds.hlds_llds.
:- import_module hlds.vartypes.
:- import_module libs.globals.
:- import_module libs.options.
:- import_module libs.trace_params.
:- import_module ll_backend.live_vars.
:- import_module ll_backend.liveness.
:- import_module ll_backend.llds.
:- import_module ll_backend.trace_gen.
:- import_module parse_tree.builtin_lib_types.
:- import_module parse_tree.prog_data.
:- import_module parse_tree.set_of_var.
:- import_module array.
:- import_module bool.
:- import_module enum.
:- import_module int.
:- import_module list.
:- import_module map.
:- import_module maybe.
:- import_module pair.
:- import_module require.
:- import_module set.
%-----------------------------------------------------------------------------%
allocate_stack_slots_in_proc(ModuleInfo, proc(PredId, ProcId), !ProcInfo) :-
initial_liveness(!.ProcInfo, PredId, ModuleInfo, Liveness0),
module_info_pred_info(ModuleInfo, PredId, PredInfo),
module_info_get_globals(ModuleInfo, Globals),
globals.get_trace_level(Globals, TraceLevel),
NeedFailVars = eff_trace_level_needs_fail_vars(ModuleInfo, PredInfo,
!.ProcInfo, TraceLevel),
(
NeedFailVars = yes,
trace_fail_vars(ModuleInfo, !.ProcInfo, FailVars)
;
NeedFailVars = no,
FailVars = set_of_var.init
),
body_should_use_typeinfo_liveness(PredInfo, Globals, TypeInfoLiveness),
globals.lookup_bool_option(Globals, opt_no_return_calls,
OptNoReturnCalls),
proc_info_get_vartypes(!.ProcInfo, VarTypes),
build_dummy_type_array(ModuleInfo, VarTypes, DummyTypeArray, DummyVars),
AllocData = alloc_data(ModuleInfo, !.ProcInfo, proc(PredId, ProcId),
TypeInfoLiveness, OptNoReturnCalls, DummyTypeArray),
NondetLiveness0 = set_of_var.init,
SimpleStackAlloc0 = stack_alloc(set.make_singleton_set(FailVars)),
proc_info_get_goal(!.ProcInfo, Goal0),
build_live_sets_in_goal_no_par_stack(Goal0, Goal, FailVars, AllocData,
SimpleStackAlloc0, SimpleStackAlloc, Liveness0, _Liveness,
NondetLiveness0, _NondetLiveness),
proc_info_set_goal(Goal, !ProcInfo),
SimpleStackAlloc = stack_alloc(LiveSets0),
do_we_need_maxfr_slot(Globals, ModuleInfo, PredInfo, !ProcInfo),
trace_reserved_slots(ModuleInfo, PredInfo, !.ProcInfo, Globals,
NumReservedSlots, MaybeReservedVarInfo),
(
MaybeReservedVarInfo = yes(ResVar - _),
ResVarSet = set_of_var.make_singleton(ResVar),
set.insert(ResVarSet, LiveSets0, LiveSets)
;
MaybeReservedVarInfo = no,
LiveSets = LiveSets0
),
graph_colour_group_elements(LiveSets, ColourSets),
set.to_sorted_list(ColourSets, ColourList),
CodeModel = proc_info_interface_code_model(!.ProcInfo),
MainStack = code_model_to_main_stack(CodeModel),
allocate_stack_slots(ColourList, Globals, MainStack, VarTypes,
NumReservedSlots, MaybeReservedVarInfo, StackSlots1),
allocate_dummy_stack_slots(DummyVars, MainStack, -1,
StackSlots1, StackSlots),
proc_info_set_stack_slots(StackSlots, !ProcInfo).
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
:- type stack_alloc
---> stack_alloc(
% Each element of this set is a set of variables
% that need to be on the stack at the same time.
set(set_of_progvar)
).
:- instance stack_alloc_info(stack_alloc) where [
pred(at_call_site/4) is alloc_at_call_site,
pred(at_resume_site/4) is alloc_at_resume_site,
pred(at_par_conj/4) is alloc_at_par_conj,
pred(at_recursive_call_for_loop_control/4) is
alloc_at_recursive_call_for_loop_control
].
:- pred alloc_at_call_site(need_across_call::in, alloc_data::in,
stack_alloc::in, stack_alloc::out) is det.
alloc_at_call_site(NeedAtCall, AllocData, !StackAlloc) :-
NeedAtCall = need_across_call(ForwardVars, ResumeVars, NondetLiveVars),
LiveSet0 = set_of_var.union_list([ForwardVars, ResumeVars,
NondetLiveVars]),
filter_out_dummy_vars(AllocData, LiveSet0, LiveSet),
!.StackAlloc = stack_alloc(LiveSets0),
LiveSets = set.insert(LiveSets0, LiveSet),
!:StackAlloc = stack_alloc(LiveSets).
:- pred alloc_at_resume_site(need_in_resume::in, alloc_data::in,
stack_alloc::in, stack_alloc::out) is det.
alloc_at_resume_site(NeedAtResume, AllocData, !StackAlloc) :-
NeedAtResume = need_in_resume(ResumeOnStack, ResumeVars, NondetLiveVars),
(
ResumeOnStack = no
;
ResumeOnStack = yes,
LiveSet0 = set_of_var.union(ResumeVars, NondetLiveVars),
filter_out_dummy_vars(AllocData, LiveSet0, LiveSet),
!.StackAlloc = stack_alloc(LiveSets0),
LiveSets = set.insert(LiveSets0, LiveSet),
!:StackAlloc = stack_alloc(LiveSets)
).
:- pred alloc_at_par_conj(need_in_par_conj::in, alloc_data::in,
stack_alloc::in, stack_alloc::out) is det.
alloc_at_par_conj(NeedParConj, AllocData, !StackAlloc) :-
NeedParConj = need_in_par_conj(StackVars0),
filter_out_dummy_vars(AllocData, StackVars0, StackVars),
!.StackAlloc = stack_alloc(LiveSets0),
LiveSets = set.insert(LiveSets0, StackVars),
!:StackAlloc = stack_alloc(LiveSets).
:- pred alloc_at_recursive_call_for_loop_control(need_for_loop_control::in,
alloc_data::in, stack_alloc::in, stack_alloc::out) is det.
alloc_at_recursive_call_for_loop_control(NeedLC, AllocData, !StackAlloc) :-
NeedLC = need_for_loop_control(StackVarsSets),
list.foldl(set_for_loop_control(AllocData), StackVarsSets, !StackAlloc).
:- pred set_for_loop_control(alloc_data::in, set_of_progvar::in,
stack_alloc::in, stack_alloc::out) is det.
set_for_loop_control(AllocData, Set0, !StackAlloc) :-
!.StackAlloc = stack_alloc(LiveSets0),
filter_out_dummy_vars(AllocData, Set0, Set),
LiveSets = set.insert(LiveSets0, Set),
!:StackAlloc = stack_alloc(LiveSets).
:- pred filter_out_dummy_vars(alloc_data::in,
set_of_progvar::in, set_of_progvar::out) is det.
filter_out_dummy_vars(AllocData, Vars, NonDummyVars) :-
DummyVarArray = AllocData ^ ad_dummy_var_array,
set_of_var.filter(var_is_not_dummy(DummyVarArray), Vars, NonDummyVars).
:- pred var_is_not_dummy(array(is_dummy_type)::in, prog_var::in) is semidet.
var_is_not_dummy(DummyVarArray, Var) :-
VarNum = to_int(Var),
array.lookup(DummyVarArray, VarNum, IsDummy),
IsDummy = is_not_dummy_type.
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
:- pred allocate_stack_slots(list(set_of_progvar)::in, globals::in,
main_stack::in, vartypes::in, int::in, maybe(pair(prog_var, int))::in,
stack_slots::out) is det.
allocate_stack_slots(ColourList, Globals, MainStack, VarTypes,
NumReservedSlots, MaybeReservedVarInfo, StackSlots) :-
% The reserved slots are referred to by fixed number
% (e.g. framevar(1)) in trace.setup.
FirstVarSlot = NumReservedSlots + 1,
allocate_stack_slots_2(ColourList, Globals, MainStack, VarTypes,
MaybeReservedVarInfo, FirstVarSlot, map.init, StackSlots).
:- pred allocate_stack_slots_2(list(set_of_progvar)::in, globals::in,
main_stack::in, vartypes::in, maybe(pair(prog_var, int))::in,
int::in, stack_slots::in, stack_slots::out) is det.
allocate_stack_slots_2([], _, _, _, _, _, !StackSlots).
allocate_stack_slots_2([Vars | VarSets], Globals, MainStack, VarTypes,
MaybeReservedVarInfo, N0, !StackSlots) :-
( float_width_on_stack(Globals, MainStack) = double_width ->
set_of_var.divide(var_is_float(VarTypes), Vars,
DoubleWidthVars, SingleWidthVars)
;
SingleWidthVars = Vars,
DoubleWidthVars = set_of_var.init
),
( set_of_var.is_non_empty(SingleWidthVars) ->
allocate_stack_slots_3(SingleWidthVars, MainStack, single_width,
MaybeReservedVarInfo, N0, N1, !StackSlots)
;
N1 = N0
),
( set_of_var.is_non_empty(DoubleWidthVars) ->
% XXX We do NOT currently allow single-width vars to overlap with
% double-width vars. The code generator does not understand that
% clobbering one of the pair of slots is equivalent to clobbering
% both of them.
align_double_width_slots(N1, N2),
allocate_stack_slots_3(DoubleWidthVars, MainStack, double_width,
MaybeReservedVarInfo, N2, N, !StackSlots)
;
N = N1
),
allocate_stack_slots_2(VarSets, Globals, MainStack, VarTypes,
MaybeReservedVarInfo, N, !StackSlots).
:- func float_width_on_stack(globals, main_stack) = stack_slot_width.
float_width_on_stack(Globals, Stack) = FloatWidth :-
% We only store unboxed double-width floats on the det stack.
% It would be possible to do on the nondet stack but we would probably
% need to pad the frame allocation at run time to ensure that any double
% variables in the frame will be at aligned memory addresses.
(
Stack = det_stack,
double_width_floats_on_det_stack(Globals, yes)
->
FloatWidth = double_width
;
FloatWidth = single_width
).
% Conform to memory alignment requirements for double-word values.
% We maintain the invariant that the stack pointer is double-aligned.
% The first stack variable is numbered 1 so all odd-numbered stack slots
% are aligned. In a downwards-growing stack a higher slot number has a
% lower address. When allocating two consecutive slots, we therefore want
% the highered-numbered slot to be ODD. [N, N+1] shall be the next slots
% to be allocated, therefore N must be EVEN and N+1 must be ODD.
%
:- pred align_double_width_slots(int::in, int::out) is det.
align_double_width_slots(N0, N) :-
( int.even(N0) ->
N = N0
;
N = N0 + 1
).
:- pred var_is_float(vartypes::in, prog_var::in) is semidet.
var_is_float(VarTypes, Var) :-
lookup_var_type(VarTypes, Var, float_type).
:- pred allocate_stack_slots_3(set_of_progvar::in, main_stack::in,
stack_slot_width::in, maybe(pair(prog_var, int))::in, int::in, int::out,
stack_slots::in, stack_slots::out) is det.
allocate_stack_slots_3(Vars, MainStack, StackSlotWidth, MaybeReservedVarInfo,
!N, !StackSlots) :-
(
MaybeReservedVarInfo = yes(ResVar - ResSlotNum),
set_of_var.member(Vars, ResVar)
->
expect(unify(StackSlotWidth, single_width), $module, $pred,
"reserved multiple stack slots"),
SlotNum = ResSlotNum
;
SlotNum = !.N,
next_slot(StackSlotWidth, !N)
),
(
MainStack = det_stack,
Locn = det_slot(SlotNum, StackSlotWidth)
;
MainStack = nondet_stack,
Locn = nondet_slot(SlotNum)
),
VarList = set_of_var.to_sorted_list(Vars),
allocate_same_stack_slot(VarList, Locn, !StackSlots).
:- pred next_slot(stack_slot_width::in, int::in, int::out) is det.
next_slot(single_width, N, N + 1).
next_slot(double_width, N, N + 2).
:- pred allocate_same_stack_slot(list(prog_var)::in, stack_slot::in,
stack_slots::in, stack_slots::out) is det.
allocate_same_stack_slot([], _Slot, !StackSlots).
allocate_same_stack_slot([Var | Vars], Slot, !StackSlots) :-
map.det_insert(Var, Slot, !StackSlots),
allocate_same_stack_slot(Vars, Slot, !StackSlots).
% We must not allocate the same stack slot to dummy variables. If we do,
% then the code that saves variables on the stack at calls will get
% confused. After saving one dummy variable on the stack, it will try
% to save the next in the same stack slot; believing the first variable
% to still be live, it will move it away.
%
% In ordinary grades, it is possible to have one value of type io.state
% and another of type store.store live at the same time; in debugging
% grades, due to our policy of extending variable lifetimes, more than
% one io.state may be live at the same time.
%
:- pred allocate_dummy_stack_slots(list(prog_var)::in, main_stack::in,
int::in, stack_slots::in, stack_slots::out) is det.
allocate_dummy_stack_slots([], _, _, !StackSlots).
allocate_dummy_stack_slots([Var | Vars], MainStack, N0, !StackSlots) :-
(
MainStack = det_stack,
Locn = det_slot(N0, single_width)
;
MainStack = nondet_stack,
Locn = nondet_slot(N0)
),
allocate_same_stack_slot([Var], Locn, !StackSlots),
allocate_dummy_stack_slots(Vars, MainStack, N0 - 1, !StackSlots).
%-----------------------------------------------------------------------------%
:- end_module ll_backend.stack_alloc.
%-----------------------------------------------------------------------------%
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