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simplify treatmenet of begin0 and discarding expressions

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Since `begin0` at the bytecode level always evaluates an initial
expression in non-tail position, we don't have to work so hard
to ensure that an extra expression sticks around.
This commit is contained in:
Gustavo Massaccesi 2014-12-01 15:20:37 -03:00 committed by Matthew Flatt
parent 60934f1415
commit 2d95c39051
2 changed files with 7 additions and 22 deletions
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17
racket/src/racket/src/compile.c
View File

@ -2926,7 +2926,7 @@ Scheme_Object *scheme_make_sequence_compilation(Scheme_Object *seq, int opt)
to a bad .zo */ to a bad .zo */
Scheme_Object *list, *v, *good; Scheme_Object *list, *v, *good;
Scheme_Sequence *o; Scheme_Sequence *o;
int count, i, k, total, last, first, setgood, addconst; int count, i, k, total, last, first, setgood;
Scheme_Type type; Scheme_Type type;
type = scheme_sequence_type; type = scheme_sequence_type;
@ -2973,23 +2973,19 @@ Scheme_Object *scheme_make_sequence_compilation(Scheme_Object *seq, int opt)
if (count == 1) { if (count == 1) {
if (opt < -1) { if (opt < -1) {
/* can't optimize away a begin0 at read time; it's too late, since the /* can't optimize away a begin0 reading a .zo time */
return is combined with EXPD_BEGIN0 */
addconst = 1;
} else if ((opt < 0) && !scheme_omittable_expr(SCHEME_CAR(seq), 1, -1, 0, NULL, NULL, 0, 0, 1)) { } else if ((opt < 0) && !scheme_omittable_expr(SCHEME_CAR(seq), 1, -1, 0, NULL, NULL, 0, 0, 1)) {
/* We can't optimize (begin0 expr cont) to expr because /* We can't optimize (begin0 expr cont) to expr because
exp is not in tail position in the original (so we'd mess exp is not in tail position in the original (so we'd mess
up continuation marks). */ up continuation marks). */
addconst = 1;
} else } else
return good; return good;
} else }
addconst = 0;
o = scheme_malloc_sequence(count + addconst); o = scheme_malloc_sequence(count);
o->so.type = ((opt < 0) ? scheme_begin0_sequence_type : scheme_sequence_type); o->so.type = ((opt < 0) ? scheme_begin0_sequence_type : scheme_sequence_type);
o->count = count + addconst; o->count = count;
--total; --total;
for (i = k = 0; i < count; k++) { for (i = k = 0; i < count; k++) {
@ -3014,9 +3010,6 @@ Scheme_Object *scheme_make_sequence_compilation(Scheme_Object *seq, int opt)
o->array[i++] = v; o->array[i++] = v;
} }
if (addconst)
o->array[i] = scheme_void;
return (Scheme_Object *)o; return (Scheme_Object *)o;
} }

12
racket/src/racket/src/optimize.c
View File

@ -4370,8 +4370,7 @@ case_lambda_shift(Scheme_Object *data, int delta, int after_depth)
static Scheme_Object * static Scheme_Object *
begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context) begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
{ {
int i, count, drop = 0, prev_size, single_result = 0, preserves_marks = 0; int i, count, drop = 0, prev_size, single_result = 0, preserves_marks = 0, kclock, sclock;
int kclock, sclock, movable;
Scheme_Sequence *s = (Scheme_Sequence *)obj; Scheme_Sequence *s = (Scheme_Sequence *)obj;
Scheme_Object *inside = NULL, *expr, *orig_first; Scheme_Object *inside = NULL, *expr, *orig_first;
int id_offset = 0; int id_offset = 0;
@ -4417,7 +4416,7 @@ begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
info->preserves_marks = 1; info->preserves_marks = 1;
info->single_result = single_result; info->single_result = single_result;
if (drop && (s->count - drop) == 1 && (preserves_marks == 1)) { if ((s->count - drop) == 1 && (preserves_marks == 1)) {
/* If the first expression preserves marks we can drop the begin0 */ /* If the first expression preserves marks we can drop the begin0 */
return s->array[0]; return s->array[0];
} }
@ -4458,13 +4457,6 @@ begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
expr = (Scheme_Object *)s2; expr = (Scheme_Object *)s2;
} }
} else { } else {
if (drop && (s->count - drop) == 1) {
/* can't drop down to 1 expression */
s->array[s->count-1] = scheme_void;
--drop;
info->size += 1;
}
if (drop) { if (drop) {
Scheme_Sequence *s2; Scheme_Sequence *s2;
int j = 0; int j = 0;