Re: [Qemu-devel] [PATCH v2 4/6] target/mips: Fix decoding mechanism of special R5900 opcodes

[Aleksandar Markovic]

> 
> From: Fredrik Noring <address@hidden>
> Subject: [PATCH v2 4/6] target/mips: Fix decoding mechanism of special R5900 
> opcodes
> 
> MOVN, MOVZ, MFHI, MFLO, MTHI, MTLO, MULT, MULTU, DIV, DIVU, DMULT,
> DMULTU, DDIV, DDIVU and JR are decoded in decode_opc_special_tx79
> instead of the generic decode_opc_special_legacy.
> 
> Signed-off-by: Fredrik Noring <address@hidden>
> ---
>  target/mips/translate.c | 54 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 50 insertions(+), 4 deletions(-)
> 

> +#if defined(TARGET_MIPS64)
> +    case OPC_DMULT:
> +    case OPC_DMULTU:
> +    case OPC_DDIV:
> +    case OPC_DDIVU:
> +        check_insn_opc_user_only(ctx, INSN_R5900);
> +        gen_muldiv(ctx, op1, 0, rs, rt);
> +        break;
> +#endif

Fredrik, do you know by any chance if a document exists that would justify 
inclusion of non-R5900 DMULT, DMULTU, DDIV, DDIVU in R5900 executables by gcc 
for R5900? Is it included by cross-gcc or by native gcc, or by both?

I think gcc folks must have had a good reason for that, some kind of design - 
it can't be 'I really like/miss this instruction, let's include it...'

Thanks,
Aleksandar