Re: [PATCH v2 08/48] tcg/optimize: Split out fold_call

[Richard Henderson]

On 10/20/21 9:05 AM, Alex Bennée wrote:
> Richard Henderson <richard.henderson@linaro.org> writes:
>
> > Calls are special in that they have a variable number
> > of arguments, and need to be able to clobber globals.
> >
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> >   tcg/optimize.c | 63 ++++++++++++++++++++++++++++++++------------------
> >   1 file changed, 41 insertions(+), 22 deletions(-)
> >
> > diff --git a/tcg/optimize.c b/tcg/optimize.c
> > index fad6f5de1f..74b9aa025a 100644
> > --- a/tcg/optimize.c
> > +++ b/tcg/optimize.c
> > @@ -624,10 +624,42 @@ static void copy_propagate(OptContext *ctx, TCGOp *op,
> >       }
> >   }
> >   
> > +static bool fold_call(OptContext *ctx, TCGOp *op)
> > +{
> > +    TCGContext *s = ctx->tcg;
> > +    int nb_oargs = TCGOP_CALLO(op);
> > +    int nb_iargs = TCGOP_CALLI(op);
> > +    int flags, i;
> > +
> > +    init_arguments(ctx, op, nb_oargs + nb_iargs);
> > +    copy_propagate(ctx, op, nb_oargs, nb_iargs);
> > +
> > +    /* If the function reads or writes globals, reset temp data. */
> > +    flags = tcg_call_flags(op);
> > +    if (!(flags & (TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_WRITE_GLOBALS))) {
> > +        int nb_globals = s->nb_globals;
>
> Aren't we missing a trick here?
>
> If the helper is going to read global registers we need to ensure any
> temps holding their data is written but we don't need to throw the
> existing temps away if the helper is TCG_CALL_NO_WRITE_GLOBALS?

Hmm, if NO_WRITE_GLOBALS, then yes, we should be able to preserve the information about 
the current contents.  There must be some quirk, though; I just don't recall what it is. 
This patch preserves existing behaviour.


r~