Re: [patch 1/4] change specific int128 -> generic intN

[Eric Botcazou <ebotcazou at adacore dot com>]

> The whole point of using _PRECISION is to have the size be exactly the
> same as the mode (bitsize is bigger than the mode for partial-int
> modes).  TYPE_SIZE_UNIT should be its storage size, right?  If the
> type is not a multiple of BITS_PER_UNIT, the actual size and
> stored-in-memory size are going to be different.

But you cannot use the PRECISION of a mode to set a size, since the SIZE of 
the mode can be used by the machine to access the object in that mode, so 
you'll end up with types whose TYPE_SIZE is smaller than the access size.

You need to use TYPE_PRECISION here.

> The problem in the old code is that BITSIZE is not the size in bits of
> the type, it's the size in bytes times BITS_PER_UNIT.  This meant that
> all partial-int modes would be converted into their non-partial modes
> eventually.  Most of my patch is about avoiding that.

Yes, BITSIZE is the size rounded up to BITS_PER_UNIT, but why is that a 
problem exactly?  Do you have modes whose size is not multiple of the unit?

> I'm not reducing it, I'm removing a case where it's rounded up.
> Rounding up a 20-bit PSImode gives you SImode eventually.

Yes, you are reducing it, the precision of bitsize must be at least that of 
sizetype + BITS_PER_UNIT_LOG + 1.

-- 
Eric Botcazou