On Fri, Sep 13, 2013 at 10:08 AM, Richard Sandiford <rdsandif...@googlemail.com> wrote: > Richard Biener <richard.guent...@gmail.com> writes: >>>> (what about partial integer modes which have weird precision (none)?) >>> >>> We don't really model that properly yet. Partial modes are just defined >>> using something like: >>> >>> PARTIAL_INT_MODE (SI); >>> >>> i.e. without the partial precision. But trunc_int_for_mode is based on >>> GET_MODE_PRECISION, so should just work if a proper precision is added. >>> (There are other places that wouldn't just work, but that's something >>> that the wide-int branch will help with. It almost feels like you were >>> setting me up for that answer. :-)) >> >> Well I was asking because if you change a GEN_INT (x) to >> gen_int_mode (PSImode, x) then you'll end up in trunc_int_for_mode with >> PSImode which looks at GET_MODE_PRECISION (PSImode is still >> a SCALAR_INT_MODE_P ...). We set precision of PSImode to -1U >> it seems, but that still means that the constant is not even canonicalized >> to the underlying mode. (so, should we set partial integer modes precision >> to the precision of the base mode? Well, of course we should simply set >> an appropriate precision at mode definition time) > > Yeah. I don't think it makes sense to canonise PSI to 32 bits when we > know it has fewer than 32 bits. It's still going to be wrong, and will > still defeat one of the main purposes of canonical constants, which is > to make equality obvious. E.g. we'd still treat PSI constants > > (const_int 0x...ff80000000) > > and > > (const_int 0x...ffc0000000) > > as different, even though they're both zero for a 24-bit PSI. > > This partial integer mode stuff is just a big hack. Like you say, > we can only really do something sensible if we know what the real > precision is. > > So I'd rather leave things as they are for this series. The precision > effectively becomes 65535 thanks to the underlying unsigned short array, > so like you say, trunc_int_for_mode is a no-op for partial modes. > Changing GEN_INT to gen_int_mode shouldn't make any difference. > > What do you think about the patch for CC modes?
I wonder if we can do without changing gen_int_mode by fixing the callers like you did for cse.c (that patch is ok). Richard. > Thanks, > Richard
