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>

2 files changed, 39 insertions, 13 deletions

diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c
index f2269a1b91..77658a88f0 100644
--- a/tcg/tcg-op.c
+++ b/tcg/tcg-op.c
@@ -84,6 +84,22 @@ void tcg_gen_op6(TCGOpcode opc, TCGArg a1, TCGArg a2, TCGArg a3,
     op->args[5] = a6;
 }
 
+/* Generic ops.  */
+
+static void add_last_as_label_use(TCGLabel *l)
+{
+    TCGLabelUse *u = tcg_malloc(sizeof(TCGLabelUse));
+
+    u->op = tcg_last_op();
+    QSIMPLEQ_INSERT_TAIL(&l->branches, u, next);
+}
+
+void tcg_gen_br(TCGLabel *l)
+{
+    tcg_gen_op1(INDEX_op_br, label_arg(l));
+    add_last_as_label_use(l);
+}
+
 void tcg_gen_mb(TCGBar mb_type)
 {
     if (tcg_ctx->gen_tb->cflags & CF_PARALLEL) {
@@ -216,8 +232,8 @@ void tcg_gen_brcond_i32(TCGCond cond, TCGv_i32 arg1, TCGv_i32 arg2, TCGLabel *l)
     if (cond == TCG_COND_ALWAYS) {
         tcg_gen_br(l);
     } else if (cond != TCG_COND_NEVER) {
-        l->refs++;
         tcg_gen_op4ii_i32(INDEX_op_brcond_i32, arg1, arg2, cond, label_arg(l));
+        add_last_as_label_use(l);
     }
 }
 
@@ -1474,7 +1490,6 @@ void tcg_gen_brcond_i64(TCGCond cond, TCGv_i64 arg1, TCGv_i64 arg2, TCGLabel *l)
     if (cond == TCG_COND_ALWAYS) {
         tcg_gen_br(l);
     } else if (cond != TCG_COND_NEVER) {
-        l->refs++;
         if (TCG_TARGET_REG_BITS == 32) {
             tcg_gen_op6ii_i32(INDEX_op_brcond2_i32, TCGV_LOW(arg1),
                               TCGV_HIGH(arg1), TCGV_LOW(arg2),
@@ -1483,6 +1498,7 @@ void tcg_gen_brcond_i64(TCGCond cond, TCGv_i64 arg1, TCGv_i64 arg2, TCGLabel *l)
             tcg_gen_op4ii_i64(INDEX_op_brcond_i64, arg1, arg2, cond,
                               label_arg(l));
         }
+        add_last_as_label_use(l);
     }
 }
 
@@ -1493,12 +1509,12 @@ void tcg_gen_brcondi_i64(TCGCond cond, TCGv_i64 arg1, int64_t arg2, TCGLabel *l)
     } else if (cond == TCG_COND_ALWAYS) {
         tcg_gen_br(l);
     } else if (cond != TCG_COND_NEVER) {
-        l->refs++;
         tcg_gen_op6ii_i32(INDEX_op_brcond2_i32,
                           TCGV_LOW(arg1), TCGV_HIGH(arg1),
                           tcg_constant_i32(arg2),
                           tcg_constant_i32(arg2 >> 32),
                           cond, label_arg(l));
+        add_last_as_label_use(l);
     }
 }
 
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;