On Wed, 15 Oct 2025, Yury Khrustalev wrote:
> On Wed, Oct 15, 2025 at 01:48:49PM +0200, Richard Biener wrote:
> > On Wed, 15 Oct 2025, Yury Khrustalev wrote:
> >
> > > Lack of DW_AT_bit_stride in a DW_TAG_array_type entry causes GDB to infer
> > > incorrect element size for vector types. The causes incorrect display of
> > > SVE predicate variables as well as out of bounds memory access when
> > > reading
> > > contents of SVE predicates from memory in GDB.
> > >
> > > We also locate DIE referenced by DW_AT_type and set DW_AT_bit_size 1 in
> > > it.
> > >
> > > ...
> > > + /* Add bit stride information to boolean vectors of single bits so that
> > > + elements can be correctly read and displayed by a debugger. */
> > > + if (VECTOR_BOOLEAN_TYPE_P (type)
> > > + && GET_MODE_CLASS (TYPE_MODE_RAW (type)) == MODE_VECTOR_BOOL)
> > > + {
> > > + /* MODE_VECTOR_BOOL implies that bit stride and bit size
> > > + for element type must be 1. */
> >
> > Is that so? I thought it wasn't.
>
> In the gcc/mode-classes.def there is:
>
> DEF_MODE_CLASS (MODE_VECTOR_BOOL), /* vectors of single bits */
>
> So, I interpreted "vector of single bits" as bit size=1 and stride=1.
Jakub answered that.
> >
> > I also think you don't want to look at modes, instead why don't
> > you check known_eq (TYPE_PRECISION (TREE_TYPE (type)), 1)?
>
> In v1 of this patch [1], I asked [2] the same thing, and the consensus
> seem to have been that we should look at modes precisely to only work on
> packed boolean vectors (TYPE_PRECISION of 1 bit is true for them but it
> also true for other types).
Which "other" VECTOR_BOOLEAN_TYPE_P types you mean? Note not all
VECTOR_BOOLEAN_TYPE_P types have 1-bit element precision.
I'll note that types is what users write and DWARF is supposed to
represent source. Modes are an implementation detail, and in
particular those might change between functions, for example to
BLKmode if not supported.
Richard.
> [1]:
> https://inbox.sourceware.org/gcc-patches/[email protected]/
>
> [2]: https://inbox.sourceware.org/gcc-patches/[email protected]/
>
> Thanks,
> Yury
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
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