tcg/mips: fix add2

The add2 code in the tcg_out_addsub2 function doesn't take into account
the case where rl == al == bl. In that case we can't compute the carry
after the addition. As it corresponds to a multiplication by 2, the
carry bit is the bit 31.

While this is a corner case, this prevents x86-64 guests to boot on a
MIPS host.

Cc: [email protected]
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Aurelien Jarno <[email protected]>

tcg/mips/tcg-target.c

@@ -1271,6 +1271,9 @@ static void tcg_out_addsub2(TCGContext *s, TCGReg rl, TCGReg rh, TCGReg al,
         if (cbl) {
             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_reg(s, OPC_ADDU, rl, al, bl);
         } else {
             tcg_out_opc_reg(s, OPC_ADDU, rl, al, bl);
             tcg_out_opc_reg(s, OPC_SLTU, TCG_TMP0, rl, (rl == bl ? al : bl));