[Bug 83658] New: Loop unrolling doesn't take into account whether it will decrease or increase performance
bugzilla-daemon at freedesktop.org
bugzilla-daemon at freedesktop.org
Tue Sep 9 03:10:22 PDT 2014
https://bugs.freedesktop.org/show_bug.cgi?id=83658
Priority: medium
Bug ID: 83658
Assignee: idr at freedesktop.org
Blocks: 77547
Summary: Loop unrolling doesn't take into account whether it
will decrease or increase performance
QA Contact: intel-3d-bugs at lists.freedesktop.org
Severity: normal
Classification: Unclassified
OS: Linux (All)
Reporter: eero.t.tamminen at intel.com
Hardware: x86-64 (AMD64)
Status: NEW
Version: git
Component: Drivers/DRI/i965
Product: Mesa
Currently loop unrolling is done in frontend. This is done based on
heuristics, not on actual data from backend whether and how much unrolling
makes sense for given HW: will unrolling run out of registers for SIMD16, how
many instructions fit into cache...
Backend should provide this kind of information for unrolling and frontend
should utilize it (either before unrolling, to control how much to do it, or
after unrolling to revert it).
(Frontend probably should be fixed to push loop invariant code outside of loop
before devoting time to improving unrolling itself.)
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