[llvm-bugs] [Bug 46808] New: RDF Live Variables Analysis may cause ballooning compile times

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46808

            Bug ID: 46808
           Summary: RDF Live Variables Analysis may cause ballooning
                    compile times
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: scott.d.constable at intel.com
                CC: llvm-bugs at lists.llvm.org

The RDF live variables analysis probably has high asymptotic complexity than
what is actually necessary. In particular:

https://github.com/llvm/llvm-project/blob/b5be1c5419e2a38eb60fc7e785567b54b6d9e0e0/llvm/lib/CodeGen/RDFLiveness.cpp#L208

This may be causing substantial compilation overhead for some users who enable
passes that depend on RDF live variable analysis, e.g.,
https://github.com/rust-lang/rust/issues/74632.

Related discussion on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2020-April/141332.html.

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