tcg/i386: use 8-bit OR or XOR for unsigned 8-bit immediates

In the case where OR or XOR has an 8-bit immediate between 128 and 255,
we can operate on a low-byte register and shorten the output by two or
three bytes (two if a prefix byte is needed for REX.B).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20231228120524.70239-1-pbonzini@redhat.com>
[rth: Incorporate into switch.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index 29e80af78bb17a7702584abbd391d133f15ced45..d268199fc1bfde7405688eecfa03e2ef3590ea65 100644 (file)
--- a/tcg/i386/tcg-target.c.inc
+++ b/tcg/i386/tcg-target.c.inc
@@ -244,6 +244,7 @@ static bool tcg_target_const_match(int64_t val, TCGType type, int ct, int vece)
 #define P_VEXL          0x80000         /* Set VEX.L = 1 */
 #define P_EVEX          0x100000        /* Requires EVEX encoding */
 
+#define OPC_ARITH_EbIb (0x80)
 #define OPC_ARITH_EvIz (0x81)
 #define OPC_ARITH_EvIb (0x83)
 #define OPC_ARITH_GvEv (0x03)          /* ... plus (ARITH_FOO << 3) */
@@ -1370,6 +1371,16 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
             return;
         }
         break;
+
+    case ARITH_OR:
+    case ARITH_XOR:
+        if (val >= 0x80 && val <= 0xff
+            && (r0 < 4 || TCG_TARGET_REG_BITS == 64)) {
+            tcg_out_modrm(s, OPC_ARITH_EbIb + P_REXB_RM, c, r0);
+            tcg_out8(s, val);
+            return;
+        }
+        break;
     }
 
     if (val == (int8_t)val) {