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From: Richard Henderson <rth@twiddle.net>
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Date: Mon, 31 Aug 2015 19:10:00 -0700
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Subject: Re: [Qemu-devel] [PATCH v14 14/33] target-tilegx: Handle simple
 logical operations
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: "walt@tilera.com" <walt@tilera.com>, Chris Metcalf <cmetcalf@ezchip.com>, QEMU Developers <qemu-devel@nongnu.org>, Chen Gang <xili_gchen_5257@hotmail.com>

On 08/29/2015 07:58 AM, Peter Maydell wrote:
> On 24 August 2015 at 17:17, Richard Henderson <rth@twiddle.net> wrote:
>> Signed-off-by: Richard Henderson <rth@twiddle.net>
>> ---
>>   target-tilegx/translate.c | 99 +++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 96 insertions(+), 3 deletions(-)
>>
>> diff --git a/target-tilegx/translate.c b/target-tilegx/translate.c
>> index a2d597d..066d351 100644
>> --- a/target-tilegx/translate.c
>> +++ b/target-tilegx/translate.c
>> @@ -106,9 +106,64 @@ static void gen_exception(DisasContext *dc, TileExcp num)
>>       dc->exit_tb = true;
>>   }
>>
>> +static bool check_gr(DisasContext *dc, uint8_t reg)
>> +{
>> +    if (likely(reg < TILEGX_R_COUNT)) {
>> +        return true;
>> +    }
>> +
>> +    switch (reg) {
>> +    case TILEGX_R_SN:
>> +    case TILEGX_R_ZERO:
>> +        break;
>> +    case TILEGX_R_IDN0:
>> +    case TILEGX_R_IDN1:
>> +        gen_exception(dc, TILEGX_EXCP_REG_IDN_ACCESS);
>> +        break;
>> +    case TILEGX_R_UDN0:
>> +    case TILEGX_R_UDN1:
>> +    case TILEGX_R_UDN2:
>> +    case TILEGX_R_UDN3:
>> +        gen_exception(dc, TILEGX_EXCP_REG_UDN_ACCESS);
>
> Why does this function generate an exception immediately
> rather than returning a TILEGX_EXCP_* code the way the
> decode framework seems to be set up to work?

So that we can simply return a TCGv from the load_gr and dest_gr functions, and 
their users don't have to check for an error code.

r~