tcg: Remove branch-to-next regardless of reference count
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>
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33
tcg/tcg.c
33
tcg/tcg.c
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@ -2637,7 +2637,7 @@ TCGOp *tcg_op_insert_after(TCGContext *s, TCGOp *old_op,
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/* Reachable analysis : remove unreachable code. */
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static void reachable_code_pass(TCGContext *s)
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{
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TCGOp *op, *op_next;
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TCGOp *op, *op_next, *op_prev;
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bool dead = false;
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QTAILQ_FOREACH_SAFE(op, &s->ops, link, op_next) {
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@ -2647,6 +2647,22 @@ static void reachable_code_pass(TCGContext *s)
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switch (op->opc) {
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case INDEX_op_set_label:
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label = arg_label(op->args[0]);
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/*
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* Optimization can fold conditional branches to unconditional.
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* If we find a label which is preceded by an unconditional
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* branch to next, remove the branch. We couldn't do this when
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* processing the branch because any dead code between the branch
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* and label had not yet been removed.
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*/
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op_prev = QTAILQ_PREV(op, link);
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if (op_prev->opc == INDEX_op_br &&
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label == arg_label(op_prev->args[0])) {
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tcg_op_remove(s, op_prev);
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/* Fall through means insns become live again. */
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dead = false;
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}
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if (label->refs == 0) {
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/*
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* While there is an occasional backward branch, virtually
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@ -2660,21 +2676,6 @@ static void reachable_code_pass(TCGContext *s)
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/* Once we see a label, insns become live again. */
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dead = false;
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remove = false;
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/*
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* Optimization can fold conditional branches to unconditional.
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* If we find a label with one reference which is preceded by
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* an unconditional branch to it, remove both. This needed to
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* wait until the dead code in between them was removed.
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*/
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if (label->refs == 1) {
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TCGOp *op_prev = QTAILQ_PREV(op, link);
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if (op_prev->opc == INDEX_op_br &&
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label == arg_label(op_prev->args[0])) {
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tcg_op_remove(s, op_prev);
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remove = true;
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}
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}
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}
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break;
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