[llvm-bugs] [Bug 36881] New: [X86] TZCNT/LZCNT/BSR/BSF have weird SchedRW

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36881

            Bug ID: 36881
           Summary: [X86] TZCNT/LZCNT/BSR/BSF have weird SchedRW
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: craig.topper at gmail.com
                CC: llvm-bugs at lists.llvm.org

BSR and BSF are using WriteShift. TZCNT/LZCNT are using WriteIMul.

I assume that generally WriteShift would be faster than WriteIMul. But
TZCNT/LZCNT are know to be better than BSR/BSF on some CPUs.

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