On 11/13/20 1:14 AM, Richard Sandiford via Gcc-patches wrote:
> This patch adds a pointer_mux<T1, T2> class that provides similar
> functionality to:
>
> union { T1 *a; T2 *b; };
> ...
> bool is_b_rather_than_a;
>
> except that the is_b_rather_than_a tag is stored in the low bit
> of the pointer. See the comments in the patch for a comparison
> between the two approaches and why this one can be more efficient.
>
> I've tried to microoptimise the class a fair bit, since a later
> patch uses it extensively in order to keep the sizes of data
> structures down.
>
> gcc/
> * mux-utils.h: New file.
Do we have any potentially bootstrappable targets where we can't
guarantee pointer alignment of at least 16 bits? I see what look like
suitable asserts, and presumably if we trigger them, then we're going to
need to rethink this and fall back to a separate bit?
jeff
