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Implement code movement for unconditional jumps.

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That is, when the destination of the jump is reachable via only the jump.
This commit is contained in:
Bill Currie 2012-05-04 18:00:05 +09:00
parent 33bfac0508
commit 5df25133b3
1 changed files with 86 additions and 2 deletions
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84
tools/qfcc/source/statements.c
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@ -1122,6 +1122,88 @@ thread_jumps (sblock_t *blocks)
}
}
static void
join_blocks (sblock_t *sblock, sblock_t *dest)
{
statement_t **s;
statement_t *g;
expr_t *label;
for (s = &sblock->statements; (*s) != (statement_t *) sblock->tail;
s = &(*s)->next)
;
debug (0, "joining blocks %p %p", sblock, dest);
unuse_label ((*s)->opa->o.label);
free_statement (*s);
sblock->tail = s;
// append dest's statements to sblock
*sblock->tail = dest->statements;
sblock->tail = dest->tail;
// clear dest's statement list
dest->tail = &dest->statements;
dest->statements = 0;
// put a goto statement into dest incase the code in sblock flows into dest
// the goto will jump to dest's old
label = new_label_expr ();
label->e.label.dest = dest->next;
label->e.label.next = dest->next->labels;
label->e.label.used++;
dest->next->labels = &label->e.label;
g = new_statement ("<GOTO>", 0);
g->opa = new_operand (op_label);
g->opa->o.label = &label->e.label;
sblock_add_statement (dest, g);
// stich dest back into the block list immediately after sblock
dest->next = sblock->next;
sblock->next = dest;
}
static int
merge_blocks (sblock_t *blocks)
{
sblock_t *sblock;
int did_something = 0;
if (!blocks)
return 0;
for (sblock = blocks; sblock; sblock = sblock->next) {
statement_t *s;
sblock_t *dest;
sblock_t *sb;
s = (statement_t *) sblock->tail;
if (!is_goto (s))
continue;
dest = s->opa->o.label->dest;
// The destination block must not be the current block
if (dest == sblock) {
warning (0, "infinite loop detected");
continue;
}
// the destiniation block must have only one label and one user for
// that label (ie, no other branch statement jumps to the block).
if (dest->labels->next || dest->labels->used > 1)
continue;
// the destination block must be otherwise unreachable (preceeded by
// an unconditional jump (goto or return))
if (dest == blocks)
continue;
for (sb = blocks; sb; sb = sb->next)
if (sb->next == dest)
break;
if (!sb) // dest is
internal_error (0, "dangling label");
s = (statement_t *) sb->tail;
if (!is_goto (s) && !is_return (s))
continue;
// desination block is reachable via only goto of the current block
sb->next = dest->next; // pull dest out of the chain
join_blocks (sblock, dest);
did_something = 1;
}
return did_something;
}
static void
remove_dead_blocks (sblock_t *blocks)
{
@ -1229,7 +1311,9 @@ make_statements (expr_t *e)
thread_jumps (sblock);
if (options.block_dot.thread)
dump_flow (sblock, "thread");
do {
remove_dead_blocks (sblock);
} while (merge_blocks (sblock));
if (options.block_dot.dead)
dump_flow (sblock, "dead");
check_final_block (sblock);