[LLVMbugs] [Bug 675] mgrid suffering 70% performance hit against native
bugzilla-daemon at cs.uiuc.edu
bugzilla-daemon at cs.uiuc.edu
Sat Feb 4 17:34:11 PST 2006
http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=675
sabre at nondot.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Component|opt |Backend: PowerPC
Product|tools |libraries
Resolution| |FIXED
Target Milestone|--- |1.7
Version|trunk |1.3
------- Additional Comments From sabre at nondot.org 2006-02-04 19:34 -------
After making codegen improvements and not getting better performance, Nate simg5'd the code.
It turns out not to be a codegen problem, but actually an alignment problem: the common block was
aligned to a 4-byte boundary (not 8) causing every load in the hot loop to fault (which flushes the
pipeline on the G5). Fixed with this patch:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060130/031641.html
We now equal GCC's performance on mgrid. Thanks to Nate for doing the analysis to figure out what
was going wrong!
-Chris
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