[m-dev.] for review: --delay-constructs

[Simon Taylor]

On Thu, Mar 08, 2001 at 06:10:08PM +1100, Zoltan Somogyi wrote:
> For review by anyone. This optimization compensates for the lack of
> construction delays in the eager code generator. On tests/benchmark/query,
> the eager code generator used to take a lot longer than the lazy code
> generator; this optimization makes them equally fast.
 
> Index: compiler/delay_construct.m
> ===================================================================

> +		Goal0 = GoalExpr0 - GoalInfo0,
> +		delay_construct_skippable_expr(GoalExpr0),
> +		goal_info_get_nonlocals(GoalInfo0, NonLocals),
> +		proc_info_maybe_complete_with_typeinfo_vars(NonLocals,
> +			DelayInfo ^ body_typeinfo_liveness,
> +			DelayInfo ^ vartypes,
> +			DelayInfo ^ type_info_varmap, CompletedNonLocals),
> +		set__intersect(CompletedNonLocals, ConstructedVars0,
> +			Intersection),
> +		set__empty(Intersection),
> +		\+ goal_info_has_feature(GoalInfo0, impure),
> +		\+ goal_info_has_feature(GoalInfo0, semipure)
> +	->
> +		delay_construct_in_conj(Goals0, DelayInfo, ConstructedVars0,
> +			RevDelayedGoals0, Goals1),
> +		Goals = [Goal0 | Goals1]
> +	;
> +		list__reverse(RevDelayedGoals0, DelayedGoals),
> +		delay_construct_in_conj(Goals0, DelayInfo, set__init, [],
> +			Goals1),
> +		list__append(DelayedGoals, [Goal0 | Goals1], Goals)
> +	).

This might cause problems with code such as:

:- type t ---> f(int, int).
:- pred p(t::in, t::out) is semidet.

p(X, Y) :-	
	% construction, A -> free, B -> free, Y -> f(free, free).
	Y = f(A, B),

	% deconstruction, A -> ground, B -> ground, Y -> ground.
	X = f(A, B),

	A > 1.

You probably need to recompute the instmap_deltas in cases like this.

Simon.
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