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Fix the old dead block removal code.

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It uses the new block merge code. Now forgotten return statements are
detected properly (naive dead block removal) and all unreachable code is
eliminated (flow analysis unreachable node removal).
This commit is contained in:
Bill Currie 2012-12-19 20:09:59 +09:00
parent ab6a3fefd9
commit b5baf0914b
1 changed files with 9 additions and 93 deletions
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102
tools/qfcc/source/statements.c
View file

@ -1433,104 +1433,16 @@ 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 (st_flow, "<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;
if (!sblock->statements)
continue;
s = (statement_t *) sblock->tail;
if (!statement_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).
// also, don't try to move a marker end-block
if (dest->labels->next || dest->labels->used > 1 || !dest->statements)
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");
if (!sb->statements)
continue;
s = (statement_t *) sb->tail;
if (!statement_is_goto (s) && !statement_is_return (s))
continue;
// desination block is reachable only via goto of the current block
if (!dest->next)
dest->next = new_sblock ();
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)
{
sblock_t *sblock;
int did_something;
int did_anything = 0;
int pass = 0;
if (!blocks)
return;
return 0;
do {
debug (0, "dead block pass %d", pass++);
@ -1584,12 +1496,14 @@ remove_dead_blocks (sblock_t *blocks)
}
unuse_label (label);
did_something = 1;
did_anything = 1;
sblock->next = sb->next;
free_sblock (sb);
}
}
} while (did_something);
return did_anything;
}
static void
@ -1637,18 +1551,20 @@ sblock_t *
make_statements (expr_t *e)
{
sblock_t *sblock = new_sblock ();
int did_something;
if (options.block_dot.expr)
dump_dot ("expr", e, dump_dot_expr);
statement_slist (sblock, e);
sblock = merge_blocks (sblock);
if (options.block_dot.initial)
dump_dot ("initial", sblock, dump_dot_sblock);
thread_jumps (sblock);
if (options.block_dot.thread)
dump_dot ("thread", sblock, dump_dot_sblock);
do {
remove_dead_blocks (sblock);
} while (merge_blocks (sblock));
did_something = remove_dead_blocks (sblock);
sblock = merge_blocks (sblock);
} while (did_something);
if (options.block_dot.dead)
dump_dot ("dead", sblock, dump_dot_sblock);
check_final_block (sblock);