[PATCH v5 18/21] powerpc64: Add prefixed instructions to instruction data type

[Christophe Leroy]

Le 08/04/2020 à 20:11, Segher Boessenkool a écrit :
> On Mon, Apr 06, 2020 at 12:25:27PM +0200, Christophe Leroy wrote:
>>> 	if (ppc_inst_prefixed(x) != ppc_inst_prefixed(y))
>>> 		return false;
>>> 	else if (ppc_inst_prefixed(x))
>>> 		return !memcmp(&x, &y, sizeof(struct ppc_inst));
>>
>> Are we sure memcmp() is a good candidate for the comparison ? Can we do
>> simpler ? Especially, I understood a prefixed instruction is a 64 bits
>> properly aligned instruction, can we do a simple u64 compare ? Or is GCC
>> intelligent enough to do that without calling memcmp() function which is
>> heavy ?
> 
> A prefixed insn is *not* 8-byte aligned, it is 4-byte aligned, fwiw.

Ah, yes, I read too fast https://patchwork.ozlabs.org/patch/1266721/

It's not 64 bits, it is 64 bytes.

> 
> memcmp() isn't as heavy as you fear, not with a non-ancient GCC at least.
> But this could be written in a nicer way, sure :-)
> 
> 
> Segher
> 

Christophe