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

[Paolo Bonzini <pbonzini@redhat.com>]

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>
---
 tcg/i386/tcg-target.c.inc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index 1791b959738..a24a23f43b1 100644
--- 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) */
@@ -1366,6 +1367,12 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
         tcg_out8(s, val);
         return;
     }
+    if (val == (uint8_t)val && (c == ARITH_OR || c == ARITH_XOR) &&
+        (r0 < 4 || TCG_TARGET_REG_BITS == 64)) {
+        tcg_out_modrm(s, OPC_ARITH_EbIb + P_REXB_RM, c, r0);
+        tcg_out8(s, val);
+        return;
+    }
     if (rexw == 0 || val == (int32_t)val) {
         tcg_out_modrm(s, OPC_ARITH_EvIz + rexw, c, r0);
         tcg_out32(s, val);
-- 
2.43.0