[Bug 86822] New: Accumulator operations drop to SIMD8 on GEN7

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86822

            Bug ID: 86822
           Summary: Accumulator operations drop to SIMD8 on GEN7
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: eero.t.tamminen at intel.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org
                CC: petri.latvala at intel.com
            Blocks: 77547

There are few games [1], which give with INTEL_DEBUG=perf following output:
SIMD16 shader unsupported, falling back to SIMD8 at a 10-20% performance cost:
SIMD16 explicit accumulator operands unsupported

This SIMD16 issue is GEN7 HW specific.  This could be worked around with
additional instructions, which can be skipped if shader falls back to SIMD8 for
some other reason.

[1] This happens at least with Planetary Annihilation & Bastion.  And it
happened also with older Mesa & older version of Crusader Kings II version (not
with latest anymore though).

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