[llvm-bugs] [Bug 25471] New: [Polly] Construction of Boundary Context is very expensive

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25471

            Bug ID: 25471
           Summary: [Polly] Construction of Boundary Context is very
                    expensive
           Product: Projects
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Polly
          Assignee: polly-dev at googlegroups.com
          Reporter: tobias at grosser.es
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 15255
  --> https://llvm.org/bugs/attachment.cgi?id=15255&action=edit
Test case

With https://llvm.org/svn/llvm-project/polly/trunk@252540 'polly-opt
-polly-scops -analyze expensive-boundary-context.ll' takes a very long time or
even aborts compilation. My current understanding is the assumptions we derive
are stored very efficiently as disjuncts, but when isl_set_complement is called 
in Scop::buildBoundaryContext the set that is constructed becomes extremely
large. It might make sense to keep the boundary constraints as disjuncts and
directly generate a run-time check from these disjuncts.

This test case took about a day to be automatically reduced from one of the LNT
benchmarks currently failing. It is the result from me setting up bugpoint to
minimize a miscompile. During this reduction bugpoint run at some point in this
compile time problem and reduced this test case instead of the original
miscompile.

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