tcg: Add liveness_pass_0

Attempt to reduce the lifetime of TEMP_TB.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 70 insertions, 0 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 71b6843eb1..1dbb24294e 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -2857,6 +2857,75 @@ static void la_cross_call(TCGContext *s, int nt)
     }
 }
 
+/*
+ * Liveness analysis: Verify the lifetime of TEMP_TB, and reduce
+ * to TEMP_EBB, if possible.
+ */
+static void __attribute__((noinline))
+liveness_pass_0(TCGContext *s)
+{
+    void * const multiple_ebb = (void *)(uintptr_t)-1;
+    int nb_temps = s->nb_temps;
+    TCGOp *op, *ebb;
+
+    for (int i = s->nb_globals; i < nb_temps; ++i) {
+        s->temps[i].state_ptr = NULL;
+    }
+
+    /*
+     * Represent each EBB by the op at which it begins.  In the case of
+     * the first EBB, this is the first op, otherwise it is a label.
+     * Collect the uses of each TEMP_TB: NULL for unused, EBB for use
+     * within a single EBB, else MULTIPLE_EBB.
+     */
+    ebb = QTAILQ_FIRST(&s->ops);
+    QTAILQ_FOREACH(op, &s->ops, link) {
+        const TCGOpDef *def;
+        int nb_oargs, nb_iargs;
+
+        switch (op->opc) {
+        case INDEX_op_set_label:
+            ebb = op;
+            continue;
+        case INDEX_op_discard:
+            continue;
+        case INDEX_op_call:
+            nb_oargs = TCGOP_CALLO(op);
+            nb_iargs = TCGOP_CALLI(op);
+            break;
+        default:
+            def = &tcg_op_defs[op->opc];
+            nb_oargs = def->nb_oargs;
+            nb_iargs = def->nb_iargs;
+            break;
+        }
+
+        for (int i = 0; i < nb_oargs + nb_iargs; ++i) {
+            TCGTemp *ts = arg_temp(op->args[i]);
+
+            if (ts->kind != TEMP_TB) {
+                continue;
+            }
+            if (ts->state_ptr == NULL) {
+                ts->state_ptr = ebb;
+            } else if (ts->state_ptr != ebb) {
+                ts->state_ptr = multiple_ebb;
+            }
+        }
+    }
+
+    /*
+     * For TEMP_TB that turned out not to be used beyond one EBB,
+     * reduce the liveness to TEMP_EBB.
+     */
+    for (int i = s->nb_globals; i < nb_temps; ++i) {
+        TCGTemp *ts = &s->temps[i];
+        if (ts->kind == TEMP_TB && ts->state_ptr != multiple_ebb) {
+            ts->kind = TEMP_EBB;
+        }
+    }
+}
+
 /* Liveness analysis : update the opc_arg_life array to tell if a
    given input arguments is dead. Instructions updating dead
    temporaries are removed. */
@@ -4872,6 +4941,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb, target_ulong pc_start)
 #endif
 
     reachable_code_pass(s);
+    liveness_pass_0(s);
     liveness_pass_1(s);
 
     if (s->nb_indirects > 0) {