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Date: Thu, 24 Oct 2013 15:42:19 -0500
From: Tom Musta <tommusta@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH 03/19] General Support for VSX Helpers
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To: Richard Henderson <rth@twiddle.net>, QEMU Developers <qemu-devel@nongnu.org>
Cc: "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>

On 10/24/2013 1:51 PM, Richard Henderson wrote:
> On 10/24/2013 09:19 AM, Tom Musta wrote:
>>
>> +#define GEN_VSX_HELPER_2(name, op1, op2, inval, type)                         \
>> +static void gen_##name(DisasContext * ctx)                                    \
>> +{                                                                             \
>> +    TCGv_i32 opc;                                                             \
>> +    if (unlikely(!ctx->vsx_enabled)) {                                        \
>> +        gen_exception(ctx, POWERPC_EXCP_VSXU);                                \
>> +        return;                                                               \
>> +    }                                                                         \
>> +    /* NIP cannot be restored if the memory exception comes from an helper */ \
>> +    gen_update_nip(ctx, ctx->nip - 4);                                        \
>> +    opc = tcg_const_i32(ctx->opcode);                                         \
>> +    gen_helper_##name(cpu_env, opc);                                          \
>> +    tcg_temp_free_i32(opc);                                                   \
>> +}
>
> I'm not a fan of delaying decode to the helpers...
>
> You're mostly doing this to avoid passing 3-4 arguments
> for the register numbers?

Because the VSRs are 128 bits wide and because there is an interesting relationship
with the FPRs and AVRs, passing 6 or more arguments would typically be required
(2 per VSR).  And, they would need to be stitched back together into a single
structure in order to use the loops in the vector routines.  I did prototype something
like this and didn't like it.

Unless you are suggesting that the decoded VSR index (0..63) be passed to the helper?