Temporary C microtile is too small sometimes

[devinamatthews]

A temporary C microtile is used in various places, such as on the diagonal of a symmetric matrix (GEMMT) where care must be taken not to write to the unstored portion. The size of this microtile is assumed to not be larger than twice the size of all vector registers together (on the assumption that "real" microtiles fit in registers plus some slack). However, several conditions cause a larger microtile to be written:

• The CRR complex case, where a complex matrix is updated by a real product. The computation is performed in the real domain, which then updates a complex microtile twice as large.
• Mixed-precision computation, for example computation is performed in single precision and then double precision output is written (which is again twice as large).

Currently, this means that a microtile may be "inflated" by as much as 4x. In the future, with a wider range of data types, this factor could be even larger.

This problems occurs concretely for the SKX configuration when doing zsssgemmt.

[devinamatthews]

Note to self: Altra has a hard-coded max stack buf size which is bad.