https://llvm.org/bugs/show_bug.cgi?id=25782
cycheng <cych...@multicorewareinc.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #2 from cycheng <cych...@multicorewareinc.com> ---
Hi Carrot,
Current Machine Block Placement provides a mechanism called "Precise (Loop)
Rotation Cost", it's aimed at this issue, and you can enable it by:
-mllvm -force-precise-rotation-cost=true (after r269267)
Performance data is available here:
(base compile option = -m64 -O3 -mcpu=power8)
http://reviews.llvm.org/D20017#428394
403.gcc got improved a lot.
davidxl plans to enable it by default.
I still saw an optimization opportunity, because his current mechanism will
bypass this pattern:
entry
|
------> loop.header (body)
|97% / \
| /50% \50%
--- latch <--- if.then
|
|3%
loop.end
And I found libquantum, h264ref can get benefit if we rotate loop top for this
pattern.
Anyway, your issue of 403.gcc is solved by "-force-precise-rotation-cost".
CY
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