tcg/mips: Improve the add2/sub2 command to use TCG_TARGET_REG_BITS

Instead of hard coding 31 for the shift right use TCG_TARGET_REG_BITS - 1.
Signed-off-by: NAlistair Francis <alistair.francis@wdc.com>
Message-Id: <7dfbddf7014a595150aa79011ddb342c3cc17ec3.1544648105.git.alistair.francis@wdc.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

tcg/mips/tcg-target.inc.c

@@ -792,7 +792,7 @@ static void tcg_out_addsub2(TCGContext *s, TCGReg rl, TCGReg rh, TCGReg al,
             tcg_out_opc_imm(s, OPC_ADDIU, rl, al, bl);
             tcg_out_opc_imm(s, OPC_SLTIU, TCG_TMP0, rl, bl);
         } else if (rl == al && rl == bl) {
-            tcg_out_opc_sa(s, OPC_SRL, TCG_TMP0, al, 31);
+            tcg_out_opc_sa(s, OPC_SRL, TCG_TMP0, al, TCG_TARGET_REG_BITS - 1);
             tcg_out_opc_reg(s, OPC_ADDU, rl, al, bl);
         } else {
             tcg_out_opc_reg(s, OPC_ADDU, rl, al, bl);