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tcg: Remove branch-to-next regardless of reference count

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Just because the label reference count is more than 1 does
not mean we cannot remove a branch-to-next.  By doing this
first, the label reference count may drop to 0, and then
the label itself gets removed as before.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2023-01-29 10:37:19 -10:00
parent 9b1890ad90
commit 4d89d0bb8f
1 changed files with 17 additions and 16 deletions
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33
tcg/tcg.c
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@ -2637,7 +2637,7 @@ TCGOp *tcg_op_insert_after(TCGContext *s, TCGOp *old_op,
/* Reachable analysis : remove unreachable code. */ /* Reachable analysis : remove unreachable code. */
static void reachable_code_pass(TCGContext *s) static void reachable_code_pass(TCGContext *s)
{ {
TCGOp *op, *op_next; TCGOp *op, *op_next, *op_prev;
bool dead = false; bool dead = false;
QTAILQ_FOREACH_SAFE(op, &s->ops, link, op_next) { QTAILQ_FOREACH_SAFE(op, &s->ops, link, op_next) {
@ -2647,6 +2647,22 @@ static void reachable_code_pass(TCGContext *s)
switch (op->opc) { switch (op->opc) {
case INDEX_op_set_label: case INDEX_op_set_label:
label = arg_label(op->args[0]); label = arg_label(op->args[0]);
/*
* Optimization can fold conditional branches to unconditional.
* If we find a label which is preceded by an unconditional
* branch to next, remove the branch. We couldn't do this when
* processing the branch because any dead code between the branch
* and label had not yet been removed.
*/
op_prev = QTAILQ_PREV(op, link);
if (op_prev->opc == INDEX_op_br &&
label == arg_label(op_prev->args[0])) {
tcg_op_remove(s, op_prev);
/* Fall through means insns become live again. */
dead = false;
}
if (label->refs == 0) { if (label->refs == 0) {
/* /*
* While there is an occasional backward branch, virtually * While there is an occasional backward branch, virtually
@ -2660,21 +2676,6 @@ static void reachable_code_pass(TCGContext *s)
/* Once we see a label, insns become live again. */ /* Once we see a label, insns become live again. */
dead = false; dead = false;
remove = false; remove = false;
/*
* Optimization can fold conditional branches to unconditional.
* If we find a label with one reference which is preceded by
* an unconditional branch to it, remove both. This needed to
* wait until the dead code in between them was removed.
*/
if (label->refs == 1) {
TCGOp *op_prev = QTAILQ_PREV(op, link);
if (op_prev->opc == INDEX_op_br &&
label == arg_label(op_prev->args[0])) {
tcg_op_remove(s, op_prev);
remove = true;
}
}
} }
break; break;