[LLVMdev] LSR is Unbearably Slow

David Greene dag at cray.com
Wed Aug 11 14:48:01 PDT 2010

I just filed bug 7872 about non-scalability of the LSR analysis
algorithms.  It may be related to bug 6727.

The fundamental problem appears to be re-running SCEV analyses such as
properlyDominates and SCEVComplexityCompare over and over again on large
SCEV expressions.  Memoizing results for SCEVComplexityCompare appears
to help significantly but that is much harder to do with things like

Is anyone actively looking at LSR compile time issues?  LLVM 2.7 is
taking on the order of 30 minutes to optimize some very simple test
cases and that's after doing the memoization work for
SCEVComplexityCompare.  TOT has the same problem.


More information about the llvm-dev mailing list