On Wed, Apr 22, 2020 at 11:41 PM Eric Botcazou <botca...@adacore.com> wrote:
>
> > What if we had this:
> > uint32_t u = 0x12345678;
> > upal_u32be_t tempb;
> > memcpy (&tempb, &u, sizeof(uint32_t));
> > uint32_t bu = tempb.val;
> >
> > Is that valid? We still run into the wrong code with the above case.
> > memcpy here should be considered a byte-by-byte copy and therefor
> > should not have any type punning except for to bytes.
>
> The usual trick of people doing type punning and pretending they don't. ;-)
> No, this cannot work as-is, although it's probably fixable by blocking the
> propagation through the memcpy in case the scalar order is flipped, unlike the
> previous example.
Yes the following is a decent workaround:
upal_u32be_t tempb;
memcpy (&tempb, &u, sizeof(uint32_t));
asm("":"+m"(tempb));
uint32_t bu = tempb.val;
But I wish this customer would not do this but they want it for some reason.
Thanks,
Andrew Pinski
>
> --
> Eric Botcazou
