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mercury/compiler/ml_optimize.m
Julien Fischer 6a7c01e483 Avoid (some) redundant levels of nesting in generated Java. 
compiler/ml_optimize.m:
    After peephole optimization of a block, if the block consists only of
    a single statement, then replace the block by the statement itself.

compiler/mlds_to_java_func.m:
    Do not output curly brackets around an MLDS function body that is a block,
    since that block will be output with its own curly brackets.
2019-09-15 20:05:19 +10:00

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% ---------------------------------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%---------------------------------------------------------------------------%
% Copyright (C) 2000-2011 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: ml_optimize.m.
% Main author: trd, fjh.
%
% This module runs various optimizations on the MLDS.
%
% Currently the optimizations we do here are
%
% - converting assignments to local variables into variable initializers.
% - eliminating initialized local variables entirely,
% by replacing occurrences of such variables with their initializer
%
% Ultimately this module should just consist of a skeleton to traverse
% the MLDS, and should call various optimization modules along the way.
%
% It would probably be a good idea to make each transformation optional.
%
%---------------------------------------------------------------------------%
:- module ml_backend.ml_optimize.
:- interface.
:- import_module libs.
:- import_module libs.globals.
:- import_module ml_backend.mlds.
:- pred mlds_optimize(globals::in, mlds::in, mlds::out) is det.
%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
:- implementation.
:- import_module backend_libs.
:- import_module backend_libs.builtin_ops.
:- import_module libs.options.
:- import_module mdbcomp.
:- import_module mdbcomp.builtin_modules.
:- import_module mdbcomp.prim_data.
:- import_module ml_backend.ml_util.
:- import_module ml_backend.mlds_dump.
:- import_module parse_tree.
:- import_module parse_tree.prog_data.
:- import_module bool.
:- import_module int.
:- import_module list.
:- import_module maybe.
:- import_module set.
%---------------------------------------------------------------------------%
:- type opt_info
---> opt_info(
oi_globals :: globals,
oi_module_name :: mlds_module_name,
oi_func_name :: mlds_function_name,
oi_func_params :: mlds_func_params
).
mlds_optimize(Globals, !MLDS) :-
ModuleName = mercury_module_name_to_mlds(!.MLDS ^ mlds_name),
% XXX We should optimize functions stored inside classes as well.
FuncDefns0 = !.MLDS ^ mlds_proc_defns,
list.map(optimize_in_function_defn(ModuleName, Globals),
FuncDefns0, FuncDefns),
!MLDS ^ mlds_proc_defns := FuncDefns.
:- pred optimize_in_function_defn(mlds_module_name::in, globals::in,
mlds_function_defn::in, mlds_function_defn::out) is det.
optimize_in_function_defn(ModuleName, Globals, FuncDefn0, FuncDefn) :-
FuncDefn0 = mlds_function_defn(Name, Context, Flags, PredProcId,
Params, FuncBody0, EnvVarNames, MaybeRequireTailrecInfo),
OptInfo = opt_info(Globals, ModuleName, Name, Params),
optimize_in_function_body(OptInfo, FuncBody0, FuncBody),
FuncDefn = mlds_function_defn(Name, Context, Flags, PredProcId,
Params, FuncBody, EnvVarNames, MaybeRequireTailrecInfo).
:- pred optimize_in_function_body(opt_info::in,
mlds_function_body::in, mlds_function_body::out) is det.
optimize_in_function_body(OptInfo, !Body) :-
(
!.Body = body_external
;
!.Body = body_defined_here(Stmt0),
optimize_in_stmt(OptInfo, Stmt0, Stmt),
trace [compile_time(flag("debug_ml_optimize")), io(!IO)] (
io.write_string("\nfunction body before\n\n", !IO),
dump_mlds_stmt(1, Stmt0, !IO),
io.write_string("\nfunction body after\n\n", !IO),
dump_mlds_stmt(1, Stmt, !IO)
),
!:Body = body_defined_here(Stmt)
).
:- pred optimize_in_maybe_stmt(opt_info::in,
maybe(mlds_stmt)::in, maybe(mlds_stmt)::out) is det.
optimize_in_maybe_stmt(OptInfo, !MaybeStmt) :-
(
!.MaybeStmt = no
;
!.MaybeStmt = yes(Stmt0),
optimize_in_stmt(OptInfo, Stmt0, Stmt),
!:MaybeStmt = yes(Stmt)
).
:- pred optimize_in_stmts(opt_info::in,
list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
optimize_in_stmts(OptInfo, !Stmts) :-
list.map(optimize_in_stmt(OptInfo), !Stmts),
Globals = OptInfo ^ oi_globals,
globals.lookup_bool_option(Globals, optimize_peep, OptPeep),
(
OptPeep = no
;
OptPeep = yes,
peephole_opt_statements(!Stmts)
).
:- pred optimize_in_stmt(opt_info::in,
mlds_stmt::in, mlds_stmt::out) is det.
optimize_in_stmt(OptInfo, Stmt0, Stmt) :-
(
Stmt0 = ml_stmt_call(_, _, _, _, _, _),
optimize_in_call_stmt(OptInfo, Stmt0, Stmt)
;
Stmt0 = ml_stmt_block(LocalVarDefns0, FuncDefns0, SubStmts0, Context),
maybe_convert_assignments_into_initializers(OptInfo,
LocalVarDefns0, LocalVarDefns1, SubStmts0, SubStmts1),
maybe_eliminate_locals(OptInfo, LocalVarDefns1, LocalVarDefns,
FuncDefns0, FuncDefns, SubStmts1, SubStmts2),
maybe_flatten_block(SubStmts2, SubStmts3),
optimize_in_stmts(OptInfo, SubStmts3, SubStmts),
% XXX We should also optimize in FuncDefns.
( if
LocalVarDefns = [],
FuncDefns = [],
SubStmts = [SubStmt]
then
Stmt = SubStmt
else
Stmt = ml_stmt_block(LocalVarDefns, FuncDefns, SubStmts, Context)
)
;
Stmt0 = ml_stmt_while(Kind, Rval, SubStmts0, LocalLoopVars, Context),
optimize_in_stmt(OptInfo, SubStmts0, SubStmts),
Stmt = ml_stmt_while(Kind, Rval, SubStmts, LocalLoopVars, Context)
;
Stmt0 = ml_stmt_if_then_else(Rval, Then0, MaybeElse0, Context),
optimize_in_stmt(OptInfo, Then0, Then),
optimize_in_maybe_stmt(OptInfo, MaybeElse0, MaybeElse),
( if
Then = ml_stmt_block([], [], [], _),
MaybeElse = yes(Else)
then
NotRval = ml_unop(logical_not, Rval),
Stmt = ml_stmt_if_then_else(NotRval, Else, no, Context)
else
Stmt = ml_stmt_if_then_else(Rval, Then, MaybeElse, Context)
)
;
Stmt0 = ml_stmt_switch(Type, Rval, Range, Cases0, Default0, Context),
list.map(optimize_in_case(OptInfo), Cases0, Cases),
optimize_in_default(OptInfo, Default0, Default),
Stmt = ml_stmt_switch(Type, Rval, Range, Cases, Default, Context)
;
Stmt0 = ml_stmt_try_commit(Ref, BodyStmt0, HandlerStmt0, Context),
optimize_in_stmt(OptInfo, BodyStmt0, BodyStmt),
optimize_in_stmt(OptInfo, HandlerStmt0, HandlerStmt),
Stmt = ml_stmt_try_commit(Ref, BodyStmt, HandlerStmt, Context)
;
( Stmt0 = ml_stmt_do_commit(_, _)
; Stmt0 = ml_stmt_return(_, _)
; Stmt0 = ml_stmt_label(_Label, _)
; Stmt0 = ml_stmt_goto(_Label, _)
; Stmt0 = ml_stmt_computed_goto(_Rval, _Label, _)
),
Stmt = Stmt0
;
Stmt0 = ml_stmt_atomic(Atomic0, Context),
( if Atomic0 = assign(TargetLval, SourceRval) then
( if
% Optimize away assignments to the dummy var, since it *should*
% only ever be assigned to; it should never be read.
TargetLval = ml_global_var(TargetGlobalVar, _TargetType),
TargetGlobalVar = global_dummy_var
then
Stmt = ml_stmt_block([], [], [], Context)
else if
% The only time the global dummy var seems to be read
% (during a bootcheck, at least) is to test whether it is
% equal to itself.
%
% We transform A == A into TRUE even if A is not a reference
% to the dummy variable, since the transformation is valid for
% any A (since mlds rvals can't cause side-effects), and
% thus testing for the dummy variable is an unnecessary cost.
%
% We don't test for other patterns (such as transforming
% A != A into FALSE) because I (zs) haven't seen the
% Mercury compiler generating such code.
SourceRval = ml_binop(BinOp, RvalA, RvalB),
RvalA = RvalB,
BinOp = eq(_)
then
Result = ml_const(mlconst_true),
Atomic = assign(TargetLval, Result),
Stmt = ml_stmt_atomic(Atomic, Context)
else
Stmt = Stmt0
)
else
Stmt = Stmt0
)
).
:- pred optimize_in_case(opt_info::in,
mlds_switch_case::in, mlds_switch_case::out) is det.
optimize_in_case(OptInfo, Case0, Case) :-
Case0 = mlds_switch_case(FirstCond, LaterConds, Stmt0),
optimize_in_stmt(OptInfo, Stmt0, Stmt),
Case = mlds_switch_case(FirstCond, LaterConds, Stmt).
:- pred optimize_in_default(opt_info::in,
mlds_switch_default::in, mlds_switch_default::out) is det.
optimize_in_default(OptInfo, Default0, Default) :-
(
Default0 = default_is_unreachable,
Default = default_is_unreachable
;
Default0 = default_do_nothing,
Default = default_do_nothing
;
Default0 = default_case(Stmt0),
optimize_in_stmt(OptInfo, Stmt0, Stmt),
Default = default_case(Stmt)
).
%---------------------------------------------------------------------------%
:- pred optimize_in_call_stmt(opt_info::in,
mlds_stmt::in(ml_stmt_is_call), mlds_stmt::out) is det.
optimize_in_call_stmt(_OptInfo, Stmt0, Stmt) :-
Stmt0 = ml_stmt_call(_Signature, FuncRval, CallArgRvals, _Results,
_IsTailCall, Context),
% If we have a self-tailcall, assign to the arguments and
% then goto the top of the tailcall loop.
( if
% Convert calls to `mark_hp' and `restore_hp' to the corresponding
% MLDS instructions. This ensures that they get generated as
% inline code. (Without this they won't, since HLDS inlining doesn't
% get run again after the add_heap_ops pass that adds these calls.)
% This approach is better than running HLDS inlining again,
% because it cheaper in compilation time.
FuncRval = ml_const(mlconst_code_addr(CodeAddr)),
CodeAddr = mlds_code_addr(QualFuncLabel, _CodeAddrSignature),
QualFuncLabel = qual_func_label(ModName, FuncLabel),
FuncLabel = mlds_func_label(ProcLabel, MaybeAux),
MaybeAux = proc_func,
ProcLabel = mlds_proc_label(PredLabel, _ProcId),
PredLabel = mlds_user_pred_label(pf_predicate, _DefnModName, PredName,
_Arity, _CodeModel, _NonOutputFunc),
(
PredName = "mark_hp",
CallArgRvals = [ml_mem_addr(Lval)],
AtomicStmt = mark_hp(Lval)
;
PredName = "restore_hp",
CallArgRvals = [Rval],
AtomicStmt = restore_hp(Rval)
),
PrivateBuiltin = mercury_private_builtin_module,
ModName = mercury_module_name_to_mlds(PrivateBuiltin)
then
Stmt = ml_stmt_atomic(AtomicStmt, Context)
else
Stmt = Stmt0
).
%----------------------------------------------------------------------------
% If the list of statements contains a block with no local variables,
% then bring the block up one level. This optimization is needed to avoid
% a compiler limit in the Microsoft C compiler (version 13.10.3077) for
% too deeply nested blocks.
%
:- pred maybe_flatten_block(list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
maybe_flatten_block(!Stmts) :-
!:Stmts = list.condense(list.map(flatten_block, !.Stmts)).
:- func flatten_block(mlds_stmt) = list(mlds_stmt).
flatten_block(Stmt) = Stmts :-
( if Stmt = ml_stmt_block([], [], BlockStmts, _) then
Stmts = BlockStmts
else
Stmts = [Stmt]
).
%---------------------------------------------------------------------------%
:- pred peephole_opt_statements(list(mlds_stmt)::in, list(mlds_stmt)::out)
is det.
peephole_opt_statements([], []).
peephole_opt_statements([Stmt0], [Stmt0]).
peephole_opt_statements([Stmt0, Stmt1 | Stmts2], Stmts) :-
( if peephole_opt_statement(Stmt0, Stmt1, Stmts2, ReplStmts) then
peephole_opt_statements(ReplStmts, Stmts)
else
peephole_opt_statements([Stmt1 | Stmts2], StmtsTail),
Stmts = [Stmt0 | StmtsTail]
).
:- pred peephole_opt_statement(mlds_stmt::in, mlds_stmt::in,
list(mlds_stmt)::in, list(mlds_stmt)::out) is semidet.
peephole_opt_statement(Stmt0, Stmt1, Stmts2, Stmts) :-
( if
% This pattern optimizes redundant tests like this:
%
% if (TestRval) {
% ...
% } else {
% ...
% }
% if (TestRval) {
% ...
% } else {
% ...
% }
%
% If neither the then-part nor the else-part of the first if-then-else
% can update any lval in TestRval, then the second test is redundant,
% and we therefore optimize it away.
%
% The pattern seems to occur mostly with semidet deconstructions.
% The semidet deconstruction tests whether the variable has the right
% functor, the then-part of that if-then-else picks up its argument
% values, there is no else part, and the next statement starts by
% testing whether the previous one succeeded, using the exact same
% condition as the semidet deconstruction.
%
% In theory, we could also apply the pattern if there were some other
% non-TestRval-affecting statements between the if-then-elses. However,
% I (zs) have not (yet) seen any code like that.
Stmt0 = ml_stmt_if_then_else(TestRval, StmtThen0, MaybeStmtElse0,
Context0),
Stmt1 = ml_stmt_if_then_else(TestRval, StmtThen1, MaybeStmtElse1,
_Context1),
find_rval_component_lvals(TestRval, set.init, TestRvalComponents),
statement_affects_lvals(TestRvalComponents, StmtThen0, no),
(
MaybeStmtElse0 = no
;
MaybeStmtElse0 = yes(StmtElse0),
statement_affects_lvals(TestRvalComponents, StmtElse0, no)
)
then
ContextThen = get_mlds_stmt_context(StmtThen0),
ThenBlockStmts0 = [StmtThen0, StmtThen1],
maybe_flatten_block(ThenBlockStmts0, ThenBlockStmts),
Then = ml_stmt_block([], [], ThenBlockStmts, ContextThen),
(
MaybeStmtElse0 = no,
(
MaybeStmtElse1 = no,
MaybeElse = no
;
MaybeStmtElse1 = yes(_),
MaybeElse = MaybeStmtElse1
)
;
MaybeStmtElse0 = yes(Else0),
(
MaybeStmtElse1 = no,
MaybeElse = MaybeStmtElse0
;
MaybeStmtElse1 = yes(Else1),
ElseBlockStmts0 = [Else0, Else1],
maybe_flatten_block(ElseBlockStmts0, ElseBlockStmts),
Else = ml_stmt_block([], [], ElseBlockStmts, Context0),
MaybeElse = yes(Else)
)
),
Stmt = ml_stmt_if_then_else(TestRval, Then, MaybeElse, Context0),
Stmts = [Stmt | Stmts2]
else if
% This pattern optimizes code like this, which we generate often
% in automatically defined type-specific comparison predicates:
%
% succeeded = (X == Y);
% succeeded = !(succeeded);
%
% This pattern replaces that with
%
% succeeded = (X != Y);
%
% because it reduces .c file size, because it may yield a speedup
% (depending on C compiler optimizations), and because it is easier
% to read when debugging generated C code.
%
% We do this only if the assignment operation is assign itself.
% We could do the same with assign_if_in_heap operations as well,
% but I (zs) have seen no need for that.
%
% Likewise, we could check for {float,str}_{eq,ne,lt,le,gt,ge}
% as well as for their integer versions, but again, I have seen
% no need for that.
% We test for the negation operation first, since we want to fail fast
% in the usual case where the pattern does not apply, and unary ops,
% and self-negations in particular, occur less frequently than
% binary ops and comparisons.
Stmt1 = ml_stmt_atomic(Atomic1, _Context1),
Atomic1 = assign(Lval, ml_unop(logical_not, ml_lval(Lval))),
Stmt0 = ml_stmt_atomic(Atomic0, Context0),
Atomic0 = assign(Lval, ml_binop(CompareOp, CmpRvalA, CmpRvalB)),
( CompareOp = eq(IntType), NegCompareOp = ne(IntType)
; CompareOp = ne(IntType), NegCompareOp = eq(IntType)
; CompareOp = int_lt(IntType), NegCompareOp = int_ge(IntType)
; CompareOp = int_le(IntType), NegCompareOp = int_gt(IntType)
; CompareOp = int_gt(IntType), NegCompareOp = int_le(IntType)
; CompareOp = int_ge(IntType), NegCompareOp = int_lt(IntType)
)
then
Atomic = assign(Lval, ml_binop(NegCompareOp, CmpRvalA, CmpRvalB)),
Stmt = ml_stmt_atomic(Atomic, Context0),
Stmts = [Stmt | Stmts2]
else
fail
).
:- pred find_rval_component_lvals(mlds_rval::in,
set(mlds_lval)::in, set(mlds_lval)::out) is det.
find_rval_component_lvals(Rval, !Components) :-
(
Rval = ml_lval(Lval),
set.insert(Lval, !Components),
find_lval_component_lvals(Lval, !Components)
;
Rval = ml_mkword(_, SubRval),
find_rval_component_lvals(SubRval, !Components)
;
( Rval = ml_box(_, SubRvalA)
; Rval = ml_unbox(_, SubRvalA)
; Rval = ml_cast(_, SubRvalA)
; Rval = ml_unop(_, SubRvalA)
),
find_rval_component_lvals(SubRvalA, !Components)
;
Rval = ml_binop(_, SubRvalA, SubRvalB),
find_rval_component_lvals(SubRvalA, !Components),
find_rval_component_lvals(SubRvalB, !Components)
;
Rval = ml_mem_addr(Lval),
set.insert(Lval, !Components),
find_lval_component_lvals(Lval, !Components)
;
( Rval = ml_const(_)
; Rval = ml_scalar_common(_)
; Rval = ml_scalar_common_addr(_)
; Rval = ml_vector_common_row_addr(_, _)
; Rval = ml_self(_)
)
).
:- pred find_lval_component_lvals(mlds_lval::in,
set(mlds_lval)::in, set(mlds_lval)::out) is det.
find_lval_component_lvals(Lval, !Components) :-
(
( Lval = ml_field(_, Rval, _, _, _)
; Lval = ml_mem_ref(Rval, _)
),
find_rval_component_lvals(Rval, !Components)
;
( Lval = ml_target_global_var_ref(_)
; Lval = ml_global_var(_, _)
; Lval = ml_local_var(_, _)
)
).
:- pred statement_affects_lvals(set(mlds_lval)::in,
mlds_stmt::in, bool::out) is det.
statement_affects_lvals(Lvals, Stmt, Affects) :-
(
Stmt = ml_stmt_block(_, _, SubStmts, _),
statements_affect_lvals(Lvals, SubStmts, Affects)
;
Stmt = ml_stmt_while(_, _, SubStmt, _, _),
statement_affects_lvals(Lvals, SubStmt, Affects)
;
Stmt = ml_stmt_if_then_else(_, Then, MaybeElse, _),
(
MaybeElse = no,
Stmts = [Then]
;
MaybeElse = yes(Else),
Stmts = [Then, Else]
),
statements_affect_lvals(Lvals, Stmts, Affects)
;
Stmt = ml_stmt_switch(_, _, _, Cases, Default, _),
cases_affect_lvals(Lvals, Cases, Affects0),
(
Affects0 = yes,
Affects = yes
;
Affects0 = no,
(
( Default = default_is_unreachable
; Default = default_do_nothing
),
Affects = no
;
Default = default_case(DefaultStmt),
statement_affects_lvals(Lvals, DefaultStmt, Affects)
)
)
;
Stmt = ml_stmt_label(_, _),
Affects = no
;
( Stmt = ml_stmt_goto(_, _)
; Stmt = ml_stmt_computed_goto(_, _, _)
; Stmt = ml_stmt_try_commit(_, _, _, _)
; Stmt = ml_stmt_do_commit(_, _)
; Stmt = ml_stmt_return(_, _)
),
Affects = yes
;
Stmt = ml_stmt_call(_, _, _, _, _, _),
% A call can update local variables even without referring to them
% explicitly, by referring to the environment in which they reside.
Affects = yes
;
Stmt = ml_stmt_atomic(AtomicStmt, _),
(
( AtomicStmt = comment(_)
; AtomicStmt = delete_object(_)
; AtomicStmt = gc_check
; AtomicStmt = restore_hp(_)
; AtomicStmt = trail_op(_)
),
Affects = no
;
( AtomicStmt = assign(Lval, _)
; AtomicStmt = assign_if_in_heap(Lval, _)
; AtomicStmt = new_object(Lval, _, _, _, _, _, _, _, _)
; AtomicStmt = mark_hp(Lval)
),
( if set.contains(Lvals, Lval) then
Affects = yes
else
Affects = no
)
;
( AtomicStmt = inline_target_code(_, _) % XXX could be improved
; AtomicStmt = outline_foreign_proc(_, _, _, _)
),
Affects = yes
)
).
:- pred statements_affect_lvals(set(mlds_lval)::in,
list(mlds_stmt)::in, bool::out) is det.
statements_affect_lvals(_, [], no).
statements_affect_lvals(Lvals, [Head | Tail], Affects) :-
statement_affects_lvals(Lvals, Head, HeadAffects),
(
HeadAffects = yes,
Affects = yes
;
HeadAffects = no,
statements_affect_lvals(Lvals, Tail, Affects)
).
:- pred cases_affect_lvals(set(mlds_lval)::in,
list(mlds_switch_case)::in, bool::out) is det.
cases_affect_lvals(_, [], no).
cases_affect_lvals(Lvals, [Head | Tail], Affects) :-
Head = mlds_switch_case(_, _, Stmt),
statement_affects_lvals(Lvals, Stmt, HeadAffects),
(
HeadAffects = yes,
Affects = yes
;
HeadAffects = no,
cases_affect_lvals(Lvals, Tail, Affects)
).
%---------------------------------------------------------------------------%
%
% This code implements the --optimize-initializations option.
% It converts MLDS code using assignments, e.g.
%
% {
% int v1; // or any other type -- it doesn't have to be int
% int v2;
% int v3;
% int v4;
% int v5;
%
% v1 = 1;
% v2 = 2;
% v3 = 3;
% foo();
% v4 = 4;
% ...
% }
%
% into code that instead uses initializers, e.g.
%
% {
% int v1 = 1;
% int v2 = 2;
% int v3 = 3;
% int v4;
%
% foo();
% v4 = 4;
% ...
% }
%
% Note that if there are multiple initializations of the same variable,
% then we will apply the optimization successively, replacing the existing
% initializers as we go, and keeping only the last, e.g.
%
% int v = 1;
% v = 2;
% v = 3;
% ...
%
% will get replaced with
%
% int v = 3;
% ...
%
% We need to watch out for some tricky cases that can't be safely optimized.
% If the RHS of the assignment refers to a variable which was declared after
% the variable whose initialization we are optimizing, e.g.
%
% int v1 = 1;
% int v2 = 0;
% v1 = v2 + 1; // RHS refers to variable declared after v1
%
% then we can't do the optimization because it would cause a forward reference:
%
% int v1 = v2 + 1; // error -- v2 not declared yet!
% int v2 = 0;
%
% Likewise if the RHS refers to the variable itself
%
% int v1 = 1;
% v1 = v1 + 1;
%
% then we can't optimize it, because that would be bogus:
%
% int v1 = v1 + 1; // error -- v1 not initialized yet!
%
% Similarly, if the initializers of the variables that follow
% the one we are trying to optimize refer to it, e.g.
%
% int v1 = 1;
% int v2 = v1 + 1; // here v2 == 2
% v1 = 0;
% ...
%
% then we can't eliminate the assignment, because that would produce
% different results:
%
% int v1 = 0;
% int v2 = v1 + 1; // wrong -- v2 == 1
% ...
:- pred maybe_convert_assignments_into_initializers(opt_info::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
maybe_convert_assignments_into_initializers(OptInfo, !Defns, !Stmts) :-
Globals = OptInfo ^ oi_globals,
% Check if --optimize-initializations is enabled.
globals.lookup_bool_option(Globals, optimize_initializations, OptInit),
(
OptInit = yes,
convert_assignments_into_initializers(OptInfo, !Defns, !Stmts)
;
OptInit = no
).
:- pred convert_assignments_into_initializers(opt_info::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
convert_assignments_into_initializers(_OptInfo, !LocalVarDefns, [], []).
convert_assignments_into_initializers(OptInfo, !LocalVarDefns,
[HeadStmt0 | TailStmts0], Stmts) :-
( if HeadStmt0 = ml_stmt_atomic(AtomicHeadStmt0, _) then
( if
% Check if the first statement in the block is an assignment
% to one of the variables declared in the block.
AtomicHeadStmt0 = assign(LHS, RHS),
LHS = ml_local_var(ThisVarName, _ThisVarType),
% We must check that the value being assigned doesn't refer to the
% variable itself.
rval_contains_var(RHS, ThisVarName) = no,
% We must check that the value being assigned doesn't refer to any
% of the variables which are declared after this one. We must also
% check that the initializers (if any) of the variables that follow
% this one don't refer to this variable.
find_this_var_defn(ThisVarName, !.LocalVarDefns, [], RevPrevDefns,
ThisVarDefn0, LaterDefns),
Filter =
( pred(OtherLocalVarDefn::in) is semidet :-
OtherLocalVarDefn = mlds_local_var_defn(OtherVarName, _,
_Type, OtherInitializer, _GC),
(
rval_contains_var(RHS, OtherVarName) = yes
;
initializer_contains_var(OtherInitializer, ThisVarName)
= yes
)
),
not list.find_first_match(Filter, LaterDefns, _)
then
% Replace the assignment statement with an initializer
% on the variable declaration.
ThisVarDefn = ThisVarDefn0 ^ mlvd_init := init_obj(RHS),
!:LocalVarDefns = list.reverse(RevPrevDefns) ++
[ThisVarDefn | LaterDefns],
% Now try to apply the same optimization again.
convert_assignments_into_initializers(OptInfo, !LocalVarDefns,
TailStmts0, Stmts)
else if
AtomicHeadStmt0 = comment(_)
then
convert_assignments_into_initializers(OptInfo, !LocalVarDefns,
TailStmts0, TailStmts),
Stmts = [HeadStmt0 | TailStmts]
else
% No optimization possible -- leave the block unchanged.
Stmts = [HeadStmt0 | TailStmts0]
)
else
% No optimization possible -- leave the block unchanged.
Stmts = [HeadStmt0 | TailStmts0]
).
:- pred find_this_var_defn(mlds_local_var_name::in,
list(mlds_local_var_defn)::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
mlds_local_var_defn::out, list(mlds_local_var_defn)::out) is semidet.
find_this_var_defn(VarName, [LocalVarDefn | LocalVarDefns], !RevPrevDefns,
ThisVarDefn, LaterDefns) :-
( if LocalVarDefn = mlds_local_var_defn(VarName, _, _, _, _) then
ThisVarDefn = LocalVarDefn,
LaterDefns = LocalVarDefns
else
!:RevPrevDefns = [LocalVarDefn | !.RevPrevDefns],
find_this_var_defn(VarName, LocalVarDefns, !RevPrevDefns,
ThisVarDefn, LaterDefns)
).
%---------------------------------------------------------------------------%
%
% This is a pass to eliminate initialized local variable definitions,
% by substituting the value of the initializer for occurrences of the variable.
%
% XXX This is quadratic in the number of variable definitions, since we do
% one pass over the block per variable definition. A more efficient algorithm
% would be to do one pass to figure out which variables could be eliminated,
% and then do another pass to actually eliminate them.
:- pred maybe_eliminate_locals(opt_info::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_function_defn)::in, list(mlds_function_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
maybe_eliminate_locals(OptInfo, !LocalVarDefns, !FuncDefns, !Stmts) :-
globals.lookup_bool_option(OptInfo ^ oi_globals, eliminate_local_vars,
EliminateLocalVars),
(
EliminateLocalVars = yes,
eliminate_locals(OptInfo, !LocalVarDefns, !FuncDefns, !Stmts)
;
EliminateLocalVars = no
).
:- pred eliminate_locals(opt_info::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_function_defn)::in, list(mlds_function_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is det.
eliminate_locals(_OptInfo, [], [], !FuncDefns, !Stmts).
eliminate_locals(OptInfo, [LocalVarDefn0 | LocalVarDefns0], LocalVarDefns,
!FuncDefns, !Stmts) :-
( if
try_to_eliminate_defn(OptInfo, LocalVarDefn0, LocalVarDefns0,
LocalVarDefns1, !FuncDefns, !Stmts)
then
eliminate_locals(OptInfo, LocalVarDefns1, LocalVarDefns,
!FuncDefns, !Stmts)
else
eliminate_locals(OptInfo, LocalVarDefns0, LocalVarDefns2,
!FuncDefns, !Stmts),
LocalVarDefns = [LocalVarDefn0 | LocalVarDefns2]
).
% This data structure holds information that we use in this pass
% to eliminate initialized local variable definitions.
:- type var_elim_info
---> var_elim_info(
% These fields remain constant.
% The name of the variable to eliminate.
var_name :: mlds_local_var_name,
% The value to replace the eliminated variable with.
var_value :: mlds_rval,
% These get updated as we go along.
% The number of occurrences of the variable.
replace_count :: int,
% `yes' if the optimization can't be applied, e.g. because
% the variable was assigned to, or because its address
% was taken.
invalidated :: bool
).
% Check if this definition is a variable that we can eliminate.
% If so, replace uses of this variable with the variable's value.
% This will fail if the definition is not a variable definition,
% or if any of the statements or definitions take the address
% of the variable, or assign to it.
%
:- pred try_to_eliminate_defn(opt_info::in, mlds_local_var_defn::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_function_defn)::in, list(mlds_function_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is semidet.
try_to_eliminate_defn(OptInfo, LocalVarDefn0, LocalVarDefns0, LocalVarDefns,
!FuncDefns, !Stmts) :-
LocalVarDefn0 = mlds_local_var_defn(VarName, _Context,
_Type, Initializer, _GCStmt),
% Check if this definition has a known initial value.
(
Initializer = init_obj(Rval)
;
Initializer = no_initializer,
find_initial_val_in_stmts(VarName, Rval, !Stmts)
;
( Initializer = init_array(_)
; Initializer = init_struct(_, _)
),
% Should we try to eliminate definitions with these kinds of
% initializers?
fail
),
% It is only safe to do this transformation if the variable's value
% is constant, otherwise we might end up moving the rvalue across
% a statement which modifies it.
rval_will_not_change(Rval),
% This transformation moves evaluation of the rvalue later in the
% computation. If the rvalue is something which might loop, throw an
% exception, or abort (e.g. for division by zero), then this might change
% the behaviour of the program. In such cases, we can only do the
% transformation if reordering of both conjunctions and disjunctions
% is allowed. (We need both permissions because can't tell here
% whether this MLDS code came from a conjunction or a disjunction.)
(
rval_cannot_throw(Rval)
;
Globals = OptInfo ^ oi_globals,
globals.lookup_bool_option(Globals, reorder_conj, yes),
globals.lookup_bool_option(Globals, reorder_disj, yes)
),
% Replace uses of this variable with the variable's value,
% checking that none of the statements or definitions took the
% address of the variable, or assigned to it.
eliminate_var(VarName, Rval, LocalVarDefns0, LocalVarDefns,
!FuncDefns, !Stmts, Count, Invalidated),
Invalidated = no,
% Make sure that we didn't duplicate the rval, unless it is just a constant
% or a variable, because duplicating any real operation would be
% a pessimization.
( Count =< 1
; rval_is_cheap_enough_to_duplicate(Rval) = yes
).
:- func rval_is_cheap_enough_to_duplicate(mlds_rval) = bool.
rval_is_cheap_enough_to_duplicate(Rval) = CheapEnough :-
(
( Rval = ml_const(_)
; Rval = ml_mem_addr(_)
; Rval = ml_self(_)
; Rval = ml_scalar_common(_)
; Rval = ml_scalar_common_addr(_)
; Rval = ml_vector_common_row_addr(_, _)
),
CheapEnough = yes
;
Rval = ml_lval(Lval),
(
( Lval = ml_local_var(_, _)
; Lval = ml_global_var(_, _)
),
CheapEnough = yes
;
( Lval = ml_mem_ref(_, _)
; Lval = ml_field(_, _, _, _, _)
; Lval = ml_target_global_var_ref(_)
),
CheapEnough = no
)
;
( Rval = ml_mkword(_, _)
; Rval = ml_box(_, _)
; Rval = ml_unbox(_, _)
; Rval = ml_unop(_, _)
; Rval = ml_binop(_, _, _)
),
% NOTE Some instances of the box and unbox operations are zero cost,
% but others are not. Since we cannot distinguish between them
% using purely local data, we take the conservative approach.
CheapEnough = no
;
Rval = ml_cast(_, SubRval),
CheapEnough = rval_is_cheap_enough_to_duplicate(SubRval)
).
% Succeed only if the specified rval definitely won't change in value.
%
:- pred rval_will_not_change(mlds_rval::in) is semidet.
rval_will_not_change(Rval) :-
require_complete_switch [Rval]
(
( Rval = ml_const(_)
; Rval = ml_scalar_common(_)
; Rval = ml_scalar_common_addr(_)
; Rval = ml_vector_common_row_addr(_, _)
)
;
Rval = ml_mem_addr(Lval),
require_complete_switch [Lval]
(
( Lval = ml_local_var(_, _)
; Lval = ml_global_var(_, _)
)
;
( Lval = ml_mem_ref(SubRval, _Type)
; Lval = ml_field(_, SubRval, _, _, _)
),
rval_will_not_change(SubRval)
;
Lval = ml_target_global_var_ref(_),
% XXX How can the address of a target language global variable
% change?
fail
)
;
( Rval = ml_mkword(_Tag, SubRval)
; Rval = ml_box(_Type, SubRval)
; Rval = ml_unbox(_Type, SubRval)
; Rval = ml_cast(_Type, SubRval)
; Rval = ml_unop(_Op, SubRval)
),
rval_will_not_change(SubRval)
;
Rval = ml_binop(_Op, SubRvalA, SubRvalB),
rval_will_not_change(SubRvalA),
rval_will_not_change(SubRvalB)
;
( Rval = ml_lval(_)
; Rval = ml_self(_)
),
fail
).
% Succeed only if the given rval definitely can't loop,
% throw an exception, or abort.
% We use a pretty conservative approximation...
%
:- pred rval_cannot_throw(mlds_rval::in) is semidet.
rval_cannot_throw(Rval) :-
require_complete_switch [Rval]
(
( Rval = ml_const(_)
; Rval = ml_scalar_common(_)
; Rval = ml_scalar_common_addr(_)
; Rval = ml_self(_)
; Rval = ml_mem_addr(_)
)
;
( Rval = ml_vector_common_row_addr(_, SubRval)
; Rval = ml_mkword(_Tag, SubRval)
; Rval = ml_box(_, SubRval)
; Rval = ml_unbox(_, SubRval)
; Rval = ml_cast(_, SubRval)
),
rval_cannot_throw(SubRval)
;
( Rval = ml_lval(_)
; Rval = ml_unop(_, _)
; Rval = ml_binop(_, _, _)
),
% Some unary and binary ops may throw, though others may not.
fail
).
% Search through a list of statements, trying to find the first assignment
% to the specified variable. Return the initial value, and a modified list
% of statements with the initial assignment deleted. Fail if the first
% value can't be determined.
%
:- pred find_initial_val_in_stmts(mlds_local_var_name::in, mlds_rval::out,
list(mlds_stmt)::in, list(mlds_stmt)::out) is semidet.
find_initial_val_in_stmts(VarName, Rval, [Stmt0 | Stmts0], Stmts) :-
( if find_initial_val_in_stmt(VarName, Rval1, Stmt0, Stmt1) then
Rval = Rval1,
( if Stmt1 = ml_stmt_block([], [], [], _) then
Stmts = Stmts0
else
Stmts = [Stmt1 | Stmts0]
)
else
% Check that Stmt0 doesn't modify the value of the variable
% -- this includes checking that there are no labels via which code
% could branch into the middle of Stmt0. Only if we are sure
% that Stmt0 can't modify the variable's value is it safe to go on
% and look for the initial value in Stmts0.
statement_contains_var(Stmt0, VarName) = no,
not (
statement_is_or_contains_statement(Stmt0, Label),
Label = ml_stmt_label(_, _)
),
find_initial_val_in_stmts(VarName, Rval, Stmts0, Stmts1),
Stmts = [Stmt0 | Stmts1]
).
:- pred find_initial_val_in_stmt(mlds_local_var_name::in, mlds_rval::out,
mlds_stmt::in, mlds_stmt::out) is semidet.
find_initial_val_in_stmt(Var, Rval, Stmt0, Stmt) :-
( if
Stmt0 = ml_stmt_atomic(AtomicStmt, Context),
AtomicStmt = assign(ml_local_var(Var, _Type), Rval0)
then
Rval = Rval0,
% Delete the assignment, by replacing it with an empty block.
Stmt = ml_stmt_block([], [], [], Context)
else if
Stmt0 = ml_stmt_block(LocalVarDefns0, FuncDefns0, SubStmts0, Context)
then
local_var_defns_contains_var(LocalVarDefns0, Var) = no,
function_defns_contains_var(FuncDefns0, Var) = no,
find_initial_val_in_stmts(Var, Rval, SubStmts0, SubStmts),
Stmt = ml_stmt_block(LocalVarDefns0, FuncDefns0, SubStmts, Context)
else
fail
).
% Replace uses of this variable with the variable's value in the specified
% definitions and statements. This will return a count of how many
% occurrences of the variable there were. It will also return
% Invalidated = yes if any of the statements or definitions take
% the address of the variable, or assign to it; in that case, the
% transformation should not be performed.
%
:- pred eliminate_var(mlds_local_var_name::in, mlds_rval::in,
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_function_defn)::in, list(mlds_function_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out,
int::out, bool::out) is det.
eliminate_var(QualVarName, VarRval, !LocalVarDefns, !FuncDefns, !Stmts,
Count, Invalidated) :-
Count0 = 0,
Invalidated0 = no,
VarElimInfo0 = var_elim_info(QualVarName, VarRval, Count0, Invalidated0),
eliminate_var_in_block(!LocalVarDefns, !FuncDefns, !Stmts,
VarElimInfo0, VarElimInfo),
Count = VarElimInfo ^ replace_count,
Invalidated = VarElimInfo ^ invalidated.
% eliminate_var_in_*:
%
% Process the specified construct, replacing all rvalue occurrences of the
% variable (^var_name) with its value (^var_value), incrementing the
% ^replace_count field for each occurrence as an rvalue, and setting
% ^invalidated to yes if the variable occurs as an lvalue.
:- pred eliminate_var_in_block(
list(mlds_local_var_defn)::in, list(mlds_local_var_defn)::out,
list(mlds_function_defn)::in, list(mlds_function_defn)::out,
list(mlds_stmt)::in, list(mlds_stmt)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_block(!LocalVarDefns, !FuncDefns, !Stmts, !VarElimInfo) :-
list.map_foldl(eliminate_var_in_local_var_defn,
!LocalVarDefns, !VarElimInfo),
list.map_foldl(eliminate_var_in_function_defn,
!FuncDefns, !VarElimInfo),
eliminate_var_in_stmts(!Stmts, !VarElimInfo).
:- pred eliminate_var_in_local_var_defn(
mlds_local_var_defn::in, mlds_local_var_defn::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_local_var_defn(LocalVarDefn0, LocalVarDefn, !VarElimInfo) :-
LocalVarDefn0 = mlds_local_var_defn(Name, Context,
Type, Initializer0, GCStmt),
eliminate_var_in_initializer(Initializer0, Initializer, !VarElimInfo),
LocalVarDefn = mlds_local_var_defn(Name, Context,
Type, Initializer, GCStmt).
:- pred eliminate_var_in_function_defn(
mlds_function_defn::in, mlds_function_defn::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_function_defn(FuncDefn0, FuncDefn, !VarElimInfo) :-
FuncDefn0 = mlds_function_defn(Name, Context, Flags, Id, Params,
Body0, EnvVarNames, MaybeRequireTailrecInfo),
(
Body0 = body_external,
Body = Body0
;
Body0 = body_defined_here(Stmt0),
eliminate_var_in_stmt(Stmt0, Stmt, !VarElimInfo),
Body = body_defined_here(Stmt)
),
FuncDefn = mlds_function_defn(Name, Context, Flags, Id, Params,
Body, EnvVarNames, MaybeRequireTailrecInfo).
:- pred eliminate_var_in_initializer(
mlds_initializer::in, mlds_initializer::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_initializer(Init0, Init, !VarElimInfo) :-
(
Init0 = no_initializer,
Init = Init0
;
Init0 = init_obj(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Init = init_obj(Rval)
;
Init0 = init_array(Elements0),
list.map_foldl(eliminate_var_in_initializer, Elements0, Elements,
!VarElimInfo),
Init = init_array(Elements)
;
Init0 = init_struct(Type, Members0),
list.map_foldl(eliminate_var_in_initializer, Members0, Members,
!VarElimInfo),
Init = init_struct(Type, Members)
).
:- pred eliminate_var_in_typed_rvals(
list(mlds_typed_rval)::in, list(mlds_typed_rval)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_typed_rvals([], [], !VarElimInfo).
eliminate_var_in_typed_rvals([TypedRval0 | TypedRvals0],
[TypedRval | TypedRvals], !VarElimInfo) :-
TypedRval0 = ml_typed_rval(Rval0, Type),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
TypedRval = ml_typed_rval(Rval, Type),
eliminate_var_in_typed_rvals(TypedRvals0, TypedRvals, !VarElimInfo).
:- pred eliminate_var_in_rvals(list(mlds_rval)::in, list(mlds_rval)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_rvals(!Rvals, !VarElimInfo) :-
list.map_foldl(eliminate_var_in_rval, !Rvals, !VarElimInfo).
:- pred eliminate_var_in_rval(mlds_rval::in, mlds_rval::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo) :-
(
Rval0 = ml_lval(Lval0),
VarName = !.VarElimInfo ^ var_name,
( if Lval0 = ml_local_var(VarName, _) then
% We found an rvalue occurrence of the variable -- replace it
% with the rval for the variable's value, and increment the counter
% for the number of occurrences that we have replaced.
Rval = !.VarElimInfo ^ var_value,
Count0 = !.VarElimInfo ^ replace_count,
!VarElimInfo ^ replace_count := Count0 + 1
else
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Rval = ml_lval(Lval)
)
;
Rval0 = ml_mkword(Tag, ArgRval0),
eliminate_var_in_rval(ArgRval0, ArgRval, !VarElimInfo),
Rval = ml_mkword(Tag, ArgRval)
;
Rval0 = ml_box(Type, ArgRval0),
eliminate_var_in_rval(ArgRval0, ArgRval, !VarElimInfo),
Rval = ml_box(Type, ArgRval)
;
Rval0 = ml_unbox(Type, ArgRval0),
eliminate_var_in_rval(ArgRval0, ArgRval, !VarElimInfo),
Rval = ml_unbox(Type, ArgRval)
;
Rval0 = ml_cast(Type, ArgRval0),
eliminate_var_in_rval(ArgRval0, ArgRval, !VarElimInfo),
Rval = ml_cast(Type, ArgRval)
;
Rval0 = ml_unop(Op, ArgRval0),
eliminate_var_in_rval(ArgRval0, ArgRval, !VarElimInfo),
Rval = ml_unop(Op, ArgRval)
;
Rval0 = ml_binop(Op, ArgRvalA0, ArgRvalB0),
eliminate_var_in_rval(ArgRvalA0, ArgRvalA, !VarElimInfo),
eliminate_var_in_rval(ArgRvalB0, ArgRvalB, !VarElimInfo),
Rval = ml_binop(Op, ArgRvalA, ArgRvalB)
;
Rval0 = ml_mem_addr(Lval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Rval = ml_mem_addr(Lval)
;
Rval0 = ml_vector_common_row_addr(VectorCommon, RowRval0),
eliminate_var_in_rval(RowRval0, RowRval, !VarElimInfo),
Rval = ml_vector_common_row_addr(VectorCommon, RowRval)
;
( Rval0 = ml_const(_)
; Rval0 = ml_scalar_common(_)
; Rval0 = ml_scalar_common_addr(_)
; Rval0 = ml_self(_)
),
Rval = Rval0
).
:- pred eliminate_var_in_lvals(list(mlds_lval)::in, list(mlds_lval)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_lvals(!Lvals, !VarElimInfo) :-
list.map_foldl(eliminate_var_in_lval, !Lvals, !VarElimInfo).
:- pred eliminate_var_in_lval(mlds_lval::in, mlds_lval::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo) :-
(
Lval0 = ml_field(MaybeTag, Rval0, PtrType, FieldId, FieldType),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Lval = ml_field(MaybeTag, Rval, PtrType, FieldId, FieldType)
;
Lval0 = ml_mem_ref(Rval0, Type),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Lval = ml_mem_ref(Rval, Type)
;
( Lval0 = ml_target_global_var_ref(_Ref)
; Lval0 = ml_global_var(_, _)
),
Lval = Lval0
;
Lval0 = ml_local_var(VarName, _Type),
invalidate_if_eliminating_local_loop_var(VarName, !VarElimInfo),
Lval = Lval0
).
:- pred eliminate_var_in_stmts(
list(mlds_stmt)::in, list(mlds_stmt)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_stmts(!Stmts, !VarElimInfo) :-
list.map_foldl(eliminate_var_in_stmt, !Stmts, !VarElimInfo).
:- pred eliminate_var_in_maybe_stmt(
maybe(mlds_stmt)::in, maybe(mlds_stmt)::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_maybe_stmt(no, no, !VarElimInfo).
eliminate_var_in_maybe_stmt(yes(Stmt0), yes(Stmt), !VarElimInfo) :-
eliminate_var_in_stmt(Stmt0, Stmt, !VarElimInfo).
:- pred eliminate_var_in_stmt(mlds_stmt::in, mlds_stmt::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_stmt(Stmt0, Stmt, !VarElimInfo) :-
(
Stmt0 = ml_stmt_block(LocalVarDefns0, FuncDefns0, SubStmts0, Context),
eliminate_var_in_block(LocalVarDefns0, LocalVarDefns,
FuncDefns0, FuncDefns, SubStmts0, SubStmts, !VarElimInfo),
Stmt = ml_stmt_block(LocalVarDefns, FuncDefns, SubStmts, Context)
;
Stmt0 = ml_stmt_while(Kind, Rval0, SubStmts0, LocalLoopVars, Context),
list.foldl(invalidate_if_eliminating_local_loop_var, LocalLoopVars,
!VarElimInfo),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
eliminate_var_in_stmt(SubStmts0, SubStmts, !VarElimInfo),
Stmt = ml_stmt_while(Kind, Rval, SubStmts, LocalLoopVars, Context)
;
Stmt0 = ml_stmt_if_then_else(Cond0, Then0, MaybeElse0, Context),
eliminate_var_in_rval(Cond0, Cond, !VarElimInfo),
eliminate_var_in_stmt(Then0, Then, !VarElimInfo),
eliminate_var_in_maybe_stmt(MaybeElse0, MaybeElse, !VarElimInfo),
Stmt = ml_stmt_if_then_else(Cond, Then, MaybeElse, Context)
;
Stmt0 = ml_stmt_switch(Type, Val0, Range, Cases0, Default0, Context),
eliminate_var_in_rval(Val0, Val, !VarElimInfo),
list.map_foldl(eliminate_var_in_case, Cases0, Cases, !VarElimInfo),
eliminate_var_in_default(Default0, Default, !VarElimInfo),
Stmt = ml_stmt_switch(Type, Val, Range, Cases, Default, Context)
;
Stmt0 = ml_stmt_label(_, _),
Stmt = Stmt0
;
Stmt0 = ml_stmt_goto(_, _),
Stmt = Stmt0
;
Stmt0 = ml_stmt_computed_goto(Rval0, Labels, Context),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Stmt = ml_stmt_computed_goto(Rval, Labels, Context)
;
Stmt0 = ml_stmt_call(Sig, Func0, Args0, RetLvals0, TailCall,
Context),
eliminate_var_in_rval(Func0, Func, !VarElimInfo),
eliminate_var_in_rvals(Args0, Args, !VarElimInfo),
eliminate_var_in_lvals(RetLvals0, RetLvals, !VarElimInfo),
Stmt = ml_stmt_call(Sig, Func, Args, RetLvals, TailCall,
Context)
;
Stmt0 = ml_stmt_return(Rvals0, Context),
eliminate_var_in_rvals(Rvals0, Rvals, !VarElimInfo),
Stmt = ml_stmt_return(Rvals, Context)
;
Stmt0 = ml_stmt_do_commit(Ref0, Context),
eliminate_var_in_rval(Ref0, Ref, !VarElimInfo),
Stmt = ml_stmt_do_commit(Ref, Context)
;
Stmt0 = ml_stmt_try_commit(Ref0, BodyStmt0, HandlerStmt0, Context),
eliminate_var_in_lval(Ref0, Ref, !VarElimInfo),
eliminate_var_in_stmt(BodyStmt0, BodyStmt, !VarElimInfo),
eliminate_var_in_stmt(HandlerStmt0, HandlerStmt, !VarElimInfo),
Stmt = ml_stmt_try_commit(Ref, BodyStmt, HandlerStmt, Context)
;
Stmt0 = ml_stmt_atomic(AtomicStmt0, Context),
eliminate_var_in_atomic_stmt(AtomicStmt0, AtomicStmt, !VarElimInfo),
Stmt = ml_stmt_atomic(AtomicStmt, Context)
).
:- pred eliminate_var_in_case(mlds_switch_case::in, mlds_switch_case::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_case(Case0, Case, !VarElimInfo) :-
Case0 = mlds_switch_case(FirstCond0, LaterConds0, Stmt0),
eliminate_var_in_case_cond(FirstCond0, FirstCond, !VarElimInfo),
list.map_foldl(eliminate_var_in_case_cond, LaterConds0, LaterConds,
!VarElimInfo),
eliminate_var_in_stmt(Stmt0, Stmt, !VarElimInfo),
Case = mlds_switch_case(FirstCond, LaterConds, Stmt).
:- pred eliminate_var_in_default(
mlds_switch_default::in, mlds_switch_default::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_default(Default0, Default, !VarElimInfo) :-
(
( Default0 = default_is_unreachable
; Default0 = default_do_nothing
),
Default = Default0
;
Default0 = default_case(Stmt0),
eliminate_var_in_stmt(Stmt0, Stmt, !VarElimInfo),
Default = default_case(Stmt)
).
:- pred eliminate_var_in_atomic_stmt(
mlds_atomic_statement::in, mlds_atomic_statement::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_atomic_stmt(Stmt0, Stmt, !VarElimInfo) :-
(
( Stmt0 = comment(_)
; Stmt0 = gc_check
),
Stmt = Stmt0
;
Stmt0 = assign(Lval0, Rval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Stmt = assign(Lval, Rval)
;
Stmt0 = assign_if_in_heap(Lval0, Rval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Stmt = assign_if_in_heap(Lval, Rval)
;
Stmt0 = delete_object(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Stmt = delete_object(Rval)
;
Stmt0 = new_object(Target0, Ptag, ExplicitSecTag, Type,
MaybeSize, MaybeCtorName, ArgRvalsTypes0, MayUseAtomic,
MaybeAllocId),
eliminate_var_in_lval(Target0, Target, !VarElimInfo),
eliminate_var_in_typed_rvals(ArgRvalsTypes0, ArgRvalsTypes,
!VarElimInfo),
Stmt = new_object(Target, Ptag, ExplicitSecTag, Type,
MaybeSize, MaybeCtorName, ArgRvalsTypes, MayUseAtomic,
MaybeAllocId)
;
Stmt0 = mark_hp(Lval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Stmt = mark_hp(Lval)
;
Stmt0 = restore_hp(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Stmt = restore_hp(Rval)
;
Stmt0 = trail_op(TrailOp0),
eliminate_var_in_trail_op(TrailOp0, TrailOp, !VarElimInfo),
Stmt = trail_op(TrailOp)
;
Stmt0 = inline_target_code(Lang, Components0),
list.map_foldl(eliminate_var_in_target_code_component,
Components0, Components, !VarElimInfo),
Stmt = inline_target_code(Lang, Components)
;
Stmt0 = outline_foreign_proc(Lang, Vs, Lvals0, Code),
eliminate_var_in_lvals(Lvals0, Lvals, !VarElimInfo),
Stmt = outline_foreign_proc(Lang, Vs, Lvals, Code)
).
:- pred eliminate_var_in_case_cond(
mlds_case_match_cond::in, mlds_case_match_cond::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_case_cond(Cond0, Cond, !VarElimInfo) :-
(
Cond0 = match_value(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Cond = match_value(Rval)
;
Cond0 = match_range(Low0, High0),
eliminate_var_in_rval(Low0, Low, !VarElimInfo),
eliminate_var_in_rval(High0, High, !VarElimInfo),
Cond = match_range(Low, High)
).
:- pred eliminate_var_in_target_code_component(
target_code_component::in, target_code_component::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_target_code_component(Component0, Component, !VarElimInfo) :-
(
( Component0 = raw_target_code(_Code)
; Component0 = user_target_code(_Code, _Context)
; Component0 = target_code_type(_Type)
; Component0 = target_code_function_name(_Name)
; Component0 = target_code_alloc_id(_AllocId)
),
Component = Component0
;
Component0 = target_code_input(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Component = target_code_input(Rval)
;
Component0 = target_code_output(Lval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Component = target_code_output(Lval)
).
:- pred eliminate_var_in_trail_op(trail_op::in, trail_op::out,
var_elim_info::in, var_elim_info::out) is det.
eliminate_var_in_trail_op(Op0, Op, !VarElimInfo) :-
(
Op0 = store_ticket(Lval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Op = store_ticket(Lval)
;
Op0 = reset_ticket(Rval0, Reason),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Op = reset_ticket(Rval, Reason)
;
( Op0 = discard_ticket
; Op0 = prune_ticket
),
Op = Op0
;
Op0 = mark_ticket_stack(Lval0),
eliminate_var_in_lval(Lval0, Lval, !VarElimInfo),
Op = mark_ticket_stack(Lval)
;
Op0 = prune_tickets_to(Rval0),
eliminate_var_in_rval(Rval0, Rval, !VarElimInfo),
Op = prune_tickets_to(Rval)
).
:- pred invalidate_if_eliminating_local_loop_var(mlds_local_var_name::in,
var_elim_info::in, var_elim_info::out) is det.
invalidate_if_eliminating_local_loop_var(VarName, !VarElimInfo) :-
( if VarName = !.VarElimInfo ^ var_name then
% We found an lvalue occurrence of the variable.
% If the variable that we are trying to eliminate
% - has its address taken, or
% - is assigned to, or
% - in general if it is used as an lvalue,
% then it is NOT safe to eliminate it.
!VarElimInfo ^ invalidated := yes
else
true
).
%---------------------------------------------------------------------------%
:- end_module ml_backend.ml_optimize.
%---------------------------------------------------------------------------%
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