tcg: don't keep dead outputs in registers

If an op with dead outputs is not removed, because it has side effects
or has multiple output and only one dead, mark the registers as dead
instead of saving them. This avoid a few register spills on TCG targets
with low register count, especially with div2 and mul2 ops, or when a
qemu_ld* result is not used (prefetch emulation for example).

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 82d3e1d..fad92f9 100644 (file)
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1782,12 +1782,16 @@ static void tcg_reg_alloc_op(TCGContext *s,
             if (!ts->fixed_reg) {
                 if (ts->val_type == TEMP_VAL_REG)
                     s->reg_to_temp[ts->reg] = -1;
-                ts->val_type = TEMP_VAL_REG;
-                ts->reg = reg;
-                /* temp value is modified, so the value kept in memory is
-                   potentially not the same */
-                ts->mem_coherent = 0; 
-                s->reg_to_temp[reg] = arg;
+                if (IS_DEAD_ARG(i)) {
+                    ts->val_type = TEMP_VAL_DEAD;
+                } else {
+                    ts->val_type = TEMP_VAL_REG;
+                    ts->reg = reg;
+                    /* temp value is modified, so the value kept in memory is
+                       potentially not the same */
+                    ts->mem_coherent = 0;
+                    s->reg_to_temp[reg] = arg;
+               }
             }
         oarg_end:
             new_args[i] = reg;
@@ -1981,10 +1985,14 @@ static int tcg_reg_alloc_call(TCGContext *s, const TCGOpDef *def,
         } else {
             if (ts->val_type == TEMP_VAL_REG)
                 s->reg_to_temp[ts->reg] = -1;
-            ts->val_type = TEMP_VAL_REG;
-            ts->reg = reg;
-            ts->mem_coherent = 0; 
-            s->reg_to_temp[reg] = arg;
+            if (IS_DEAD_ARG(i)) {
+                ts->val_type = TEMP_VAL_DEAD;
+            } else {
+                ts->val_type = TEMP_VAL_REG;
+                ts->reg = reg;
+                ts->mem_coherent = 0;
+                s->reg_to_temp[reg] = arg;
+            }
         }
     }