On Thu, Jan 08, 2026 at 08:50:35AM -0700, Jeffrey Law wrote:
> > +bool
> > +riscv_bitint_type_info (int n, struct bitint_info *info)
> > +{
> > + if (n <= 8)
> > + info->limb_mode = QImode;
> > + else if (n <= 16)
> > + info->limb_mode = HImode;
> > + else if (n <= 32)
> > + info->limb_mode = SImode;
> > + else if (n <= 64)
> > + info->limb_mode = DImode;
> > + else if (n <= 128 && TARGET_64BIT)
> > + info->limb_mode = TImode;
> > + else
> > + info->limb_mode = TARGET_64BIT ? DImode : SImode;
> So I've never looked at how BitInt works, so if this is totally off-base
> just say so ;-)
>
> It seems a bit odd to have the limb_mode by DImode for rv32 when we don't
> have any DImode operations in rv32. Though we allow TImode for rv64, so
> perhaps we're just relying on widening capabilities in the expander
> interfaces under the hood?
>
> It also seems a bit odd that for n > 128 and TARGET_64BIT that we select
> DImode when we use TImode for sizes > 64, but <= 128. Similarly for
> !TARGET_64BIT we have SImode and DImode respectively.
It depends on what the psABI says (if it says anything at all).
What Kito posted is quite usual thing (except for the abi_limb_mode !=
limb_mode && extended = true case which still needs to have a few spots
in the generic handling tweaked (like for arm32).
The above with that
+ info->abi_limb_mode = info->limb_mode;
+
+ if (n > 64 && TARGET_64BIT)
+ info->abi_limb_mode = TImode;
+
+ if (n > 32 && !TARGET_64BIT)
+ info->abi_limb_mode = DImode;
after it means that for TARGET_64BIT, up to _BitInt(128) those
are passed and handled like char/short/int/long long/__int128 (or unsigned
versions thereof) and for _BitInt(129) and above it is handled as
structure containing array of __int128 elements for passing/alignment,
but code emitted by compiler and libgcc handles it as array of long long
elements.
And similarly for !TARGET_64BIT ditto except the boundary is _BitInt(64)
and instead of __int128 in the above it is long long and instead of long
long elements int elements.
So, it will use 2 words only for the _BitInt(65) to _BitInt(128)
case (resp. _BitInt(33) to _BitInt(64)) and for larger stuff it will
use initially straight line code, then loops working on word-sized elements.
Jakub
