6441f1c9d5
This patch proposes new a tuning feature string format that helps users
to build a performance model by "configuring" an existing tune CPU,
along with its scheduling model. For example, this string
```
"sifive-x280:single-element-vec-fp64"
```
takes ``sifive-x280`` as the "base" tune CPU and configured it with
``single-element-vec-fp64``. This gives us a performance model that
looks exactly like that of ``sifive-x280``, except some of the 64-bit
vector floating point instructions now produce only a single element per
cycle due to ``single-element-vec-fp64``.
This string could eventually be used in places like ``-mtune`` at the
frontend. Right now, this patch only implements the parser part, which
is put under the TargetParser library.
The grammar for this string is:
```
tune-cpu ::= 'tuning CPU name in lower case'
directive ::= "[a-zA-Z0-9_-]+"
tune-features ::= directive ["," directive]*
```
A *directive* can and can only _enable_ or _disable_ a certain tuning
feature from the tuning CPU. A **positive directive**, like the
``single-element-vec-fp64`` we just saw, enables an additional tuning
feature in the associated tuning model.
A **negative directive**, on the other hand, removes a certain tuning
feature. For example, ``sifive-x390`` already has the
``single-element-vec-fp64`` feature, and we can use
"sifive-x390:no-single-element-vec-fp64" to create a new performance
model that looks nearly the same as ``sifive-x390`` except
``single-element-vec-fp64`` being cut out. In this case,
``no-single-element-vec-fp64`` is a negative directive.
There are additional restrictions on what we can put in the list of
directives, please refer to the documentations for more details.
Right now, this string only accepts directives that are explicitly
supported by the tune CPU. For example, "sifive-x280:prefer-w-inst" is
not a valide string as ``prefer-w-inst`` is not supported by
``sifive-x280`` at this moment. Vendors of these processors are expected
to maintain the compatibility of their supported directives across
different versions.
---------
Co-authored-by: Sam Elliott <aelliott@qti.qualcomm.com>
15 KiB
15 KiB