[Mesa-dev] Merge criteria for glsl2 branch

[Ian Romanick]

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As everyone knows, a group of us at Intel have been rewriting Mesa's
GLSL compiler.  The work started out-of-tree as a stand alone compiler.
 We moved all of our work to the glsl2 branch in the Mesa tree as soon
as we had some actual code being generated.  This was about month ago.
Since that time we have implemented quite a bit more code generation and
a complete linker.  The compiler is not done, but it gets closer every day.

I think now is the time to start discussing merge criteria.  It is well
known that the Intel graphics team favors quarterly releases.  In order
to align with other people's release schedules, we'd really like to have
the new compiler in a Mesa release at the end of Q3 (end of September /
beginning of October).  That's just over two months from now.  In order
to have a credible release, the compiler needs to be merged to master
before then.  A reasonable estimate puts the end of August as the latest
possible merge time.  Given how far the compiler has come in the last
month, I have a lot of faith in being able to hit that target.

We have developed our own set of merge requirements, and these are
listed below.  Since this is such a large subsystem, we want to solicit
input from the other stakeholders.

 * No piglit regressions, except draw_buffers-05.vert, compared to
    master in swrast, i965, or i915.

 * Any failing tests do not crash (segfault, assertion failure, etc.).

draw_buffers-05.vert is specifically excluded because I'm not sure the
test is correct.

One of the items on the TODO list is proper support for GLSL ES.  That
work won't happen until the last couple weeks of August, so I don't
think any sort of ES testing is suitable merge criteria.  Unless, of
course, the tests in question should also work on desktop GLSL.

We haven't and, for all practical purposes, can't test with Gallium or
other hardware drivers.  The new compiler generates the same assembly IR
that the current compiler generates.  We haven't added any instructions.
 It does, however, generate different combinations of instructions,
different uses of registers, and so on.  We don't expect there to be
significant impact on other hardware, but there may be some.  The
optimizer in r300 will certainly see different sequences of instructions
than it is accustomed to seeing.  I can't foresee what impact this will
have on that driver.

I have put up the results of master and the glsl2 branch at
http://people.freedesktop.org/~idr/results/.  This run off
compiler.tests from the glsl2 branch of Eric's piglit repository.  A few
of the failures (half a dozen or so) on master seem to be mutex related
in the GLX code.  Kristian is working on fixing that. :)

We're already very close to our proposed merge criteria.

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