[LLVMbugs] [Bug 18607] New: SCEV extreme compile time and memory usage with sequence of muls in loop

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18607

            Bug ID: 18607
           Summary: SCEV extreme compile time and memory usage with
                    sequence of muls in loop
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Global Analyses
          Assignee: unassignedbugs at nondot.org
          Reporter: Matthew.Arsenault at amd.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 11935
  --> http://llvm.org/bugs/attachment.cgi?id=11935&action=edit
Reduced testcase

opt -indvars on this testcase, which consists of a large sequence of muls
inside a loop seems to never complete and gets stuck spinning in SCEV. The time
seems to be from GroupByComplexity being repeatedly called with a vector with a
constantly increasing by Fibonacci number of items.

The number of muls can be cut down, and then it runs fast enough to see that it
does actually complete, but then it still takes several seconds.

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