[PATCH] dwarf2out: Fix up field_byte_offset [PR101378]

[Jakub Jelinek]

On Wed, Nov 10, 2021 at 12:36:04PM +0100, Richard Biener wrote:
> > I'm afraid I forgot the DECL_FIELD_OFFSET vs. DECL_FIELD_BIT_OFFSET stuff
> > enough that I'm not sure what is the right fix for that case, maybe it would
> > work if we dropped the && TREE_CODE (DECL_FIELD_OFFSET (decl)) == INTEGER_CST
> > check and instead used:
> > -      bitpos_int = wi::to_offset (DECL_FIELD_BIT_OFFSET (decl));
> > +      if (TREE_CODE (DECL_FIELD_OFFSET (decl)) == INTEGER_CST)
> > +	bitpos_int = wi::to_offset (bit_position (decl));
> > +      else
> > +	bitpos_int = wi::to_offset (DECL_FIELD_BIT_OFFSET (decl));
> > at the start and
> > -      if (ctx->variant_part_offset == NULL_TREE)
> > +      if (ctx->variant_part_offset == NULL_TREE
> > +	  && TREE_CODE (DECL_FIELD_OFFSET (decl)) == INTEGER_CST)
> >          {
> >            *cst_offset = object_offset_in_bytes.to_shwi ();
> >            return NULL;
> >          }
> >        tree_result = wide_int_to_tree (sizetype, object_offset_in_bytes);
> > +      if (TREE_CODE (DECL_FIELD_OFFSET (decl)) == INTEGER_CST)
> > +	tree_result = size_binop (PLUS_EXPR, DECL_FIELD_OFFSET (decl),
> > +				  tree_result);
> 
> that needs multiplication by BITS_PER_UNIT.

I don't think so.
>From bit_from_pos and byte_from_pos functions it is clear that
DECL_FIELD_OFFSET is in bytes and DECL_FIELD_BIT_OFFSET in bits.
And object_offset_in_bytes is in bytes too.

> 
> > or so.
> 
> Not sure if it's worth special-casing constant DECL_FIELD_OFFSET
> though, or whether the code can just work with DECL_FIELD_BIT_OFFSET
> and DECL_FIELD_OFFSET be always added.

It has certainly the advantage that it doesn't change anything for the
most common case (where DECL_FIELD_OFFSET is INTEGER_CST).

	Jakub