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From: Richard Henderson <rth@twiddle.net>
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Date: Wed, 10 Feb 2016 04:25:12 +1100
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Subject: Re: [Qemu-devel] [PATCH 11/15] tcg-mips: Use mips64r6 instructions
	in tcg_out_movi
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To: James Hogan <james.hogan@imgtec.com>
Cc: qemu-devel@nongnu.org, aurelien@aurel32.net

On 02/10/2016 03:50 AM, James Hogan wrote:
> I think ret and 0 are the wrong way around here. You're putting 0 in rs
> (the destination register), which causes a seg fault.
>
> OUT: [size=56]
> 0xfff30b0064:  lw       s1,-8(s0)
> 0xfff30b0068:  bnezalc  zero,s1,0xfff30b0090
> 0xfff30b006c:  nop
> 0xfff30b0070:  j        0xfff0000000
> 0xfff30b0074:  nop
> 0xfff30b0078:  lui      s1,0xbfc0
> 0xfff30b007c:  ori      s1,s1,0x580
> 0xfff30b0080:  sd       s1,256(s0)
> 0xfff30b0084:  aluipc   zero,0xfeb7
> 0xfff30b0088:  j        0xfff30b0034
> 0xfff30b008c:  ori      v0,v0,0x4010
> 0xfff30b0090:  aluipc   zero,0xfeb7
> 0xfff30b0094:  j        0xfff30b0034
> 0xfff30b0098:  ori      v0,v0,0x4013
>
> Cheers
> James
>
>
>
>> +        } else {
>> +            TCGReg in = TCG_REG_ZERO;
>> +            tcg_target_long tmp = (int16_t)arg;
>> +
>> +            /* The R6 manual recommends construction of immediates in
>> +               order of low to high (ADDI, AUI, DAHI, DATI) in order
>> +               to simplify hardware recognizing these sequences.  */
>> +
>> +            if (tmp) {
>> +                tcg_out_opc_imm(s, OPC_ADDIU, ret, in, tmp);
>> +                in = ret;
>> +            }
>> +            arg = (arg - tmp) >> 16;
>> +            tmp = (int16_t)arg;
>> +
>> +            /* Note that DAHI and DATI only have one register operand,
>> +               and are thus we must put a zero low part in place.  Also
>> +               note that we already eliminated simple 32-bit constants
>> +               so we know this must happen.  */
>> +            if (tmp || in != ret) {
>> +                tcg_out_opc_imm(s, OPC_AUI, ret, in, tmp);
>> +            }
>> +            arg = (arg - tmp) >> 16;
>> +            tmp = (int16_t)arg;
>> +
>> +            if (tmp) {
>> +                tcg_out_opc_imm(s, OPC_DAHI, ret, 0, tmp);
>> +            }
>> +            arg = (arg - tmp) >> 16;
>> +            tcg_debug_assert(arg == (int16_t)arg);
>> +
>> +            if (arg) {
>> +                tcg_out_opc_imm(s, OPC_DATI, ret, 0, arg);

Same mistake here for DAHI/DATI.


r~