[llvm-bugs] [Bug 49527] New: extraneous dynamic swizzle when all lanes are equal and constant

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49527

            Bug ID: 49527
           Summary: extraneous dynamic swizzle when all lanes are equal
                    and constant
           Product: new-bugs
           Version: 11.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: danielwatson311 at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

When the vector being shuffled has equal elements/lanes, LLVM should skip the
shuffle/swizzle.

As far as I can tell this only affects dynamic swizzles like AVX2's VPERMD and
does not affect constant shuffles like SHUFPS.

VPERMD: https://godbolt.org/z/eeKWfx
shufflevector: https://godbolt.org/z/9b6r7x

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