Re: [Qemu-devel] [PATCH 3/8] target-ppc: Bug Fix: rlwimi

[Tom Musta <tommusta@gmail.com>]

On 8/15/2014 3:05 PM, Richard Henderson wrote:
> On 08/11/2014 09:23 AM, Tom Musta wrote:
>> Also fix the special case of MB=31 and ME=0 to copy the entire contents
>> of the source GPR.
> 
> Err, that's not what you did.
> 
>>      if (likely(sh == 0 && mb == 0 && me == 31)) {
>> +#if defined(TARGET_PPC64)
>> +        tcg_gen_mov_i64(cpu_gpr[rA(ctx->opcode)], cpu_gpr[rS(ctx->opcode)]);
>> +#else
>>          tcg_gen_ext32u_tl(cpu_gpr[rA(ctx->opcode)], cpu_gpr[rS(ctx->opcode)]);
>> +#endif
> 
> This is the reverse condition.  Which, true enough, should not be implemented
> with ext32u for PPC64.  But a MOV isn't right either, it is
> 
>   deposit(ra, rs, 0, 32)
> 
> Which does point out that we should probably implement anything MB <= ME and SH
> == 31 - ME with the deposit opcode.
> 
> 
> r~
> 

Richard:

Good catch.  I found a bug in my test generator ... rlwimi is unusual in that the
"RA" register is both a source and a target.  A fix is forthcoming.

Thanks also for your other comments.  Unlike this one, I believe they are optimizations.
I will investigate and potentially publish some additional changes.  Alex has already
taken this series into his ppc-next, so the new patches will be relative to these.