[llvm-bugs] [Bug 50155] New: [InstCombine] Taking an order of magnitude longer in 12.0.0 than in 10.0.0 for some examples.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50155

            Bug ID: 50155
           Summary: [InstCombine] Taking an order of magnitude longer in
                    12.0.0 than in 10.0.0 for some examples.
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: christine.andress at metrics.ca
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Created attachment 24809
  --> https://bugs.llvm.org/attachment.cgi?id=24809&action=edit
gzipped ir module exhibiting much slower InstCombine optimization pass.

For some functions, the --instcombine optimization takes excessively longer
with llvm 12.0.0 than it does with llvm 10.0.0.

In the attached example, a run of "opt -o=out.o --instcombine test_instcomb.ir"
takes 53 seconds, where it used to take around 2 seconds when version 10.0.0
was used (albeit version 12.0.0 combines more instructions).

Is there a way to mitigate this speed performance degradation when using the
library interface (i.e. from C++ library API, not from the opt tool)?

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