tcg/i386: Use shift in tcg_out_setcond

For LT/GE vs zero, shift down the sign bit.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/i386/tcg-target.c.inc

@@ -1578,6 +1578,21 @@ static void tcg_out_setcond(TCGContext *s, int rexw, TCGCond cond,
         }
         return;
 
+    case TCG_COND_GE:
+        inv = true;
+        /* fall through */
+    case TCG_COND_LT:
+        /* If arg2 is 0, extract the sign bit. */
+        if (const_arg2 && arg2 == 0) {
+            tcg_out_mov(s, rexw ? TCG_TYPE_I64 : TCG_TYPE_I32, dest, arg1);
+            if (inv) {
+                tcg_out_modrm(s, OPC_GRP3_Ev + rexw, EXT3_NOT, dest);
+            }
+            tcg_out_shifti(s, SHIFT_SHR + rexw, dest, rexw ? 63 : 31);
+            return;
+        }
+        break;
+
     default:
         break;
     }