tcg: Link branches to the labels

This allows us to easily find all branches that use a label.
Since 'refs' is only tested vs zero, remove it and test for
an empty list instead.  Drop the use of bitfields, which had
been used to pack refs into a single 32-bit word.

Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 20 insertions, 10 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 6b830ade4c..0b93359d3c 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -283,6 +283,7 @@ TCGLabel *gen_new_label(void)
 
     memset(l, 0, sizeof(TCGLabel));
     l->id = s->nb_labels++;
+    QSIMPLEQ_INIT(&l->branches);
     QSIMPLEQ_INIT(&l->relocs);
 
     QSIMPLEQ_INSERT_TAIL(&s->labels, l, next);
@@ -2520,23 +2521,32 @@ static void process_op_defs(TCGContext *s)
     }
 }
 
-void tcg_op_remove(TCGContext *s, TCGOp *op)
+static void remove_label_use(TCGOp *op, int idx)
 {
-    TCGLabel *label;
+    TCGLabel *label = arg_label(op->args[idx]);
+    TCGLabelUse *use;
 
+    QSIMPLEQ_FOREACH(use, &label->branches, next) {
+        if (use->op == op) {
+            QSIMPLEQ_REMOVE(&label->branches, use, TCGLabelUse, next);
+            return;
+        }
+    }
+    g_assert_not_reached();
+}
+
+void tcg_op_remove(TCGContext *s, TCGOp *op)
+{
     switch (op->opc) {
     case INDEX_op_br:
-        label = arg_label(op->args[0]);
-        label->refs--;
+        remove_label_use(op, 0);
         break;
     case INDEX_op_brcond_i32:
     case INDEX_op_brcond_i64:
-        label = arg_label(op->args[3]);
-        label->refs--;
+        remove_label_use(op, 3);
         break;
     case INDEX_op_brcond2_i32:
-        label = arg_label(op->args[5]);
-        label->refs--;
+        remove_label_use(op, 5);
         break;
     default:
         break;
@@ -2648,7 +2658,7 @@ reachable_code_pass(TCGContext *s)
                 dead = false;
             }
 
-            if (label->refs == 0) {
+            if (QSIMPLEQ_EMPTY(&label->branches)) {
                 /*
                  * While there is an occasional backward branch, virtually
                  * all branches generated by the translators are forward.
@@ -4892,7 +4902,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb, target_ulong pc_start)
         bool error = false;
 
         QSIMPLEQ_FOREACH(l, &s->labels, next) {
-            if (unlikely(!l->present) && l->refs) {
+            if (unlikely(!l->present) && !QSIMPLEQ_EMPTY(&l->branches)) {
                 qemu_log_mask(CPU_LOG_TB_OP,
                               "$L%d referenced but not present.\n", l->id);
                 error = true;