[Qemu-devel] [PATCH v3 2/6] Add copy and constant propagation.

[Kirill Batuzov]

Make tcg_constant_folding do copy and constant propagation. It is a
preparational work before actual constant folding.

Signed-off-by: Kirill Batuzov <address@hidden>
---
 tcg/optimize.c |  182 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 180 insertions(+), 2 deletions(-)

diff --git a/tcg/optimize.c b/tcg/optimize.c
index c7c7da9..f8afe71 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -40,24 +40,196 @@
         glue(glue(case INDEX_op_, x), _i32)
 #endif
 
+typedef enum {
+    TCG_TEMP_UNDEF = 0,
+    TCG_TEMP_CONST,
+    TCG_TEMP_COPY,
+    TCG_TEMP_HAS_COPY,
+    TCG_TEMP_ANY
+} tcg_temp_state;
+
+struct tcg_temp_info {
+    tcg_temp_state state;
+    uint16_t prev_copy;
+    uint16_t next_copy;
+    tcg_target_ulong val;
+};
+
+static struct tcg_temp_info temps[TCG_MAX_TEMPS];
+
+/* Reset TEMP's state to TCG_TEMP_ANY.  If TEMP was a representative of some
+   class of equivalent temp's, a new representative should be chosen in this
+   class. */
+static void reset_temp(TCGArg temp, int nb_temps, int nb_globals)
+{
+    int i;
+    TCGArg new_base = (TCGArg)-1;
+    if (temps[temp].state == TCG_TEMP_HAS_COPY) {
+        for (i = temps[temp].next_copy; i != temp; i = temps[i].next_copy) {
+            if (i >= nb_globals) {
+                temps[i].state = TCG_TEMP_HAS_COPY;
+                new_base = i;
+                break;
+            }
+        }
+        for (i = temps[temp].next_copy; i != temp; i = temps[i].next_copy) {
+            if (new_base == (TCGArg)-1) {
+                temps[i].state = TCG_TEMP_ANY;
+            } else {
+                temps[i].val = new_base;
+            }
+        }
+        temps[temps[temp].next_copy].prev_copy = temps[temp].prev_copy;
+        temps[temps[temp].prev_copy].next_copy = temps[temp].next_copy;
+    } else if (temps[temp].state == TCG_TEMP_COPY) {
+        temps[temps[temp].next_copy].prev_copy = temps[temp].prev_copy;
+        temps[temps[temp].prev_copy].next_copy = temps[temp].next_copy;
+        new_base = temps[temp].val;
+    }
+    temps[temp].state = TCG_TEMP_ANY;
+    if (new_base != (TCGArg)-1 && temps[new_base].next_copy == new_base) {
+        temps[new_base].state = TCG_TEMP_ANY;
+    }
+}
+
+static int op_bits(int op)
+{
+    switch (op) {
+    case INDEX_op_mov_i32:
+        return 32;
+#if TCG_TARGET_REG_BITS == 64
+    case INDEX_op_mov_i64:
+        return 64;
+#endif
+    default:
+        fprintf(stderr, "Unrecognized operation %d in op_bits.\n", op);
+        tcg_abort();
+    }
+}
+
+static int op_to_movi(int op)
+{
+    switch (op_bits(op)) {
+    case 32:
+        return INDEX_op_movi_i32;
+#if TCG_TARGET_REG_BITS == 64
+    case 64:
+        return INDEX_op_movi_i64;
+#endif
+    default:
+        fprintf(stderr, "op_to_movi: unexpected return value of "
+                "function op_bits.\n");
+        tcg_abort();
+    }
+}
+
+static void tcg_opt_gen_mov(TCGArg *gen_args, TCGArg dst, TCGArg src,
+                            int nb_temps, int nb_globals)
+{
+        reset_temp(dst, nb_temps, nb_globals);
+        assert(temps[src].state != TCG_TEMP_COPY);
+        if (src >= nb_globals) {
+            assert(temps[src].state != TCG_TEMP_CONST);
+            if (temps[src].state != TCG_TEMP_HAS_COPY) {
+                temps[src].state = TCG_TEMP_HAS_COPY;
+                temps[src].next_copy = src;
+                temps[src].prev_copy = src;
+            }
+            temps[dst].state = TCG_TEMP_COPY;
+            temps[dst].val = src;
+            temps[dst].next_copy = temps[src].next_copy;
+            temps[dst].prev_copy = src;
+            temps[temps[dst].next_copy].prev_copy = dst;
+            temps[src].next_copy = dst;
+        }
+        gen_args[0] = dst;
+        gen_args[1] = src;
+}
+
+static void tcg_opt_gen_movi(TCGArg *gen_args, TCGArg dst, TCGArg val,
+                             int nb_temps, int nb_globals)
+{
+        reset_temp(dst, nb_temps, nb_globals);
+        temps[dst].state = TCG_TEMP_CONST;
+        temps[dst].val = val;
+        gen_args[0] = dst;
+        gen_args[1] = val;
+}
+
+/* Propagate constants and copies, fold constant expressions. */
 static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
                                     TCGArg *args, TCGOpDef *tcg_op_defs)
 {
-    int i, nb_ops, op_index, op, nb_temps, nb_globals;
+    int i, nb_ops, op_index, op, nb_temps, nb_globals, nb_call_args;
     const TCGOpDef *def;
     TCGArg *gen_args;
+    /* Array VALS has an element for each temp.
+       If this temp holds a constant then its value is kept in VALS' element.
+       If this temp is a copy of other ones then this equivalence class'
+       representative is kept in VALS' element.
+       If this temp is neither copy nor constant then corresponding VALS'
+       element is unused. */
 
     nb_temps = s->nb_temps;
     nb_globals = s->nb_globals;
+    memset(temps, 0, nb_temps * sizeof(struct tcg_temp_info));
 
     nb_ops = tcg_opc_ptr - gen_opc_buf;
     gen_args = args;
     for (op_index = 0; op_index < nb_ops; op_index++) {
         op = gen_opc_buf[op_index];
         def = &tcg_op_defs[op];
+        /* Do copy propagation */
+        if (!(def->flags & (TCG_OPF_CALL_CLOBBER | TCG_OPF_SIDE_EFFECTS))) {
+            assert(op != INDEX_op_call);
+            for (i = def->nb_oargs; i < def->nb_oargs + def->nb_iargs; i++) {
+                if (temps[args[i]].state == TCG_TEMP_COPY) {
+                    args[i] = temps[args[i]].val;
+                }
+            }
+        }
+
+        /* Propagate constants through copy operations and do constant
+           folding.  Constants will be substituted to arguments by register
+           allocator where needed and possible.  Also detect copies. */
         switch (op) {
+        CASE_OP_32_64(mov):
+            if ((temps[args[1]].state == TCG_TEMP_COPY
+                && temps[args[1]].val == args[0])
+                || args[0] == args[1]) {
+                args += 2;
+                gen_opc_buf[op_index] = INDEX_op_nop;
+                break;
+            }
+            if (temps[args[1]].state != TCG_TEMP_CONST) {
+                tcg_opt_gen_mov(gen_args, args[0], args[1],
+                                nb_temps, nb_globals);
+                gen_args += 2;
+                args += 2;
+                break;
+            }
+            /* Source argument is constant.  Rewrite the operation and
+               let movi case handle it. */
+            op = op_to_movi(op);
+            gen_opc_buf[op_index] = op;
+            args[1] = temps[args[1]].val;
+            /* fallthrough */
+        CASE_OP_32_64(movi):
+            tcg_opt_gen_movi(gen_args, args[0], args[1], nb_temps, nb_globals);
+            gen_args += 2;
+            args += 2;
+            break;
         case INDEX_op_call:
-            i = (args[0] >> 16) + (args[0] & 0xffff) + 3;
+            nb_call_args = (args[0] >> 16) + (args[0] & 0xffff);
+            if (!(args[nb_call_args + 1] & (TCG_CALL_CONST | TCG_CALL_PURE))) {
+                for (i = 0; i < nb_globals; i++) {
+                    reset_temp(i, nb_temps, nb_globals);
+                }
+            }
+            for (i = 0; i < (args[0] >> 16); i++) {
+                reset_temp(args[i + 1], nb_temps, nb_globals);
+            }
+            i = nb_call_args + 3;
             while (i) {
                 *gen_args = *args;
                 args++;
@@ -69,6 +241,7 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t 
*tcg_opc_ptr,
         case INDEX_op_jmp:
         case INDEX_op_br:
         CASE_OP_32_64(brcond):
+            memset(temps, 0, nb_temps * sizeof(struct tcg_temp_info));
             for (i = 0; i < def->nb_args; i++) {
                 *gen_args = *args;
                 args++;
@@ -76,6 +249,11 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t 
*tcg_opc_ptr,
             }
             break;
         default:
+            /* Default case: we do know nothing about operation so no
+               propagation is done.  We only trash output args.  */
+            for (i = 0; i < def->nb_oargs; i++) {
+                reset_temp(args[i], nb_temps, nb_globals);
+            }
             for (i = 0; i < def->nb_args; i++) {
                 gen_args[i] = args[i];
             }
-- 
1.7.4.1