Re: [PATCH 0/6] target/mips: Convert Loongson LEXT opcodes to decodetree

[Philippe Mathieu-Daudé]

On 1/13/21 3:15 AM, Jiaxun Yang wrote:
> 在 2021/1/13 上午5:54, Philippe Mathieu-Daudé 写道:
>> Loongson is next step in the "MIPS decodetree conversion" epic.
>> Start with the simplest extension.
>>
>> The diffstat addition comes from the TCG functions expanded.
>> The code is easier to review now.
>> IMO this is also a good template to show how easy a decodetree
>> conversion can be (and how nice the .decode file is to review) :P
>>
>> Please review,
>>
>> Phil.
>>
>> Based-on: <20210112184156.2014305-1-f4bug@amsat.org>
>>            "decodetree: Allow 'dot' in opcode names"
>>
>> Philippe Mathieu-Daudé (6):
>>    target/mips: Re-introduce OPC_ADDUH_QB_DSP and OPC_MUL_PH_DSP
>>    target/mips: Convert Loongson DDIV.G opcodes to decodetree
>>    target/mips: Convert Loongson DIV.G opcodes to decodetree
>>    target/mips: Convert Loongson [D]DIVU.G opcodes to decodetree
>>    target/mips: Convert Loongson [D]MOD[U].G opcodes to decodetree
>>    target/mips: Convert Loongson [D]MULT[U].G opcodes to decodetree
>>
>>   target/mips/translate.h       |   1 +
>>   target/mips/godson2.decode    |  29 +++
>>   target/mips/loong-ext.decode  |  30 +++
> 
> Hi Philippe,
> 
> Thanks for the template!
> 
> Just a small question, where should we perform ISA availability check?
> Before calling generated decoder or after decoded?

The check is done before in decode_loongson:

 bool decode_loongson(DisasContext *ctx, uint32_t insn)
 {
     if ((ctx->insn_flags & INSN_LOONGSON2E)
         // if ISA available ...
             && decode_godson2(ctx, ctx->opcode)) {
             // and opcode supported
         // return success
         return true;
     }
     // else keep going ...

     if ((ctx->insn_flags & ASE_LEXT)
             && decode_loong_ext(ctx, ctx->opcode)) {
         return true;
     }

     // finally return false, if nothing else decoded
     // gen_reserved_instruction will be called in the
     // main decode loop.
     return false;
 }

> 
> Loong-EXT is a super set of Loongson2F's Godson2 and MMI instructions,
> how could we tell it?

MMI instructions are currently handled by the ASE_LMMI flag,
a different decoder (which will also be handled by this function,
similarly to ASE_LEXT).

Regards,

Phil.