Re: [PATCH v3 41/48] tcg/optimize: Sink commutative operand swapping into fold functions

[Richard Henderson]

On 10/26/21 9:27 AM, Alex Bennée wrote:
> I find this a bit magical. I couldn't find anything about TCGArg except
> it's type:
>
>    typedef tcg_target_ulong TCGArg;

For an argument that contains a temp,

static inline TCGArg temp_arg(TCGTemp *ts)
{
    return (uintptr_t)ts;
}

static inline TCGTemp *arg_temp(TCGArg a)
{
    return (TCGTemp *)(uintptr_t)a;
}

i.e. the TCGArg is in fact a pointer.

> so I'm not sure what to make of -1 in this case. I guess it just means
> we never have a (sum == 0 && dest == a2) leg but it's not obvious
> reading the fold code.

Indeed.  The use of -1 goes back quite a ways.  How about

#define NO_DEST  temp_arg(NULL)

which will also fail to match in that expression?


r~