On Tue, Oct 07, 2025 at 06:55:25PM +0000, Tamar Christina wrote:
> > ...
> >
> > In general we should produce DWARF based on the type, not the mode. It’s
> > supposed to map to the source, not the target. The layout of a svebool is
> > the
> > same with or without SVE enabled, no?
>
> You're right, the svbool_t specifically is always registered with VNx16BI, so
> It'll always be single bit precision. So in that regard Yury's patch is
> correct if we
> only ever put out DWARF for svbool_t.
>
> I however don't know what the expected experience here is.
>
> Consider:
>
> #include <arm_sve.h>
>
> svbool_t f8 ()
> {
> return svptrue_b8 ();
> }
>
> svbool_t f16 ()
> {
> return svptrue_b16 ();
> }
>
> The first one has every bit significant, and the second one it's every 2nd
> bit.
> But with DW_AT_bit_stride = 1, I'm not sure how a user in GDB is able to tell
> If the register values belong to a predicate where every other lane is
> inactive
> or one where every entry is active.
The way I understand it is that DWARF would have information about svbool_t type
only. A variable of this type (i.e. a predicate) would have different meaning
depending on what type it is applied to. A pattern like
1 0 0 0 1 0 0 0 .. 0
might mean
{ true, true, false, ... }
for svuint32_t, but it would mean
{ true, false, true, false, true, false ... }
for svuint16_t. So, as far as the *type* is concerned, using stride of 1 bit
makes sense to me.
Thanks,
Yury
