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Implement jump threading.

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First real optimization :)
This commit is contained in:
Bill Currie 2012-05-03 17:42:58 +09:00
parent 78a9ba2557
commit 43b5edf46b
2 changed files with 49 additions and 0 deletions
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33
tools/qfcc/source/statements.c
View file

@ -1036,6 +1036,37 @@ remove_label_from_dest (ex_label_t *label)
}
}
static void
thread_jumps (sblock_t *blocks)
{
sblock_t *sblock;
ex_label_t *label, *l;
statement_t *s;
if (!blocks)
return;
for (sblock = blocks; sblock->next; sblock = sblock->next) {
s = (statement_t *) sblock->tail;
if (!strcmp (s->opcode, "<GOTO>"))
label = s->opa->o.label;
else if (!strncmp (s->opcode, "<IF", 3))
label = s->opb->o.label;
else
continue;
for (l = label;
(l->dest->statements
&& !strcmp (l->dest->statements->opcode, "<GOTO>"));
l = l->dest->statements->opa->o.label) {
}
if (l != label) {
if (!strcmp (s->opcode, "<GOTO>"))
s->opa->o.label = l;
else if (!strncmp (s->opcode, "<IF", 3))
s->opb->o.label = l;
}
}
}
static void
remove_dead_blocks (sblock_t *blocks)
{
@ -1127,6 +1158,8 @@ make_statements (expr_t *e)
sblock_t *sblock = new_sblock ();
// print_expr (e);
statement_slist (sblock, e);
// print_flow (sblock);
thread_jumps (sblock);
// print_flow (sblock);
remove_dead_blocks (sblock);
// print_flow (sblock);

16
tools/qfcc/test/thread-jumps.r Normal file
View file

@ -0,0 +1,16 @@
int
foo (int bar)
{
int x, y;
for (x = 0; x < bar; x++) {
for (y = 0; y < bar; y++) {
if (x * y > bar)
break;
else
continue;
}
break;
}
return x * y;
}