[llvm-bugs] [Bug 46896] New: InstCombine - extend matchRotate to handle funnel shifts

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46896

            Bug ID: 46896
           Summary: InstCombine - extend matchRotate to handle funnel
                    shifts
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: llvm-bugs at lists.llvm.org, spatel+llvm at rotateright.com

matchRotate currently only matches rotations, but should be able to handle
funnel shifts as well with minimal effort:

define i64 @rotvar(i64 %a0, i64 %a1, i64 %a2) {
  %m = and i64 %a2, 63
  %n = sub i64 0, %m
  %s = and i64 %n, 63
  %1 = shl i64 %a0, %m
  %2 = lshr i64 %a0, %s
  %3 = or i64 %1, %2
  ret i64 %3
}

define i64 @fshvar(i64 %a0, i64 %a1, i64 %a2) {
  %m = and i64 %a2, 63
  %n = sub i64 0, %m
  %s = and i64 %n, 63
  %1 = shl i64 %a0, %m
  %2 = lshr i64 %a1, %s
  %3 = or i64 %1, %2
  ret i64 %3
}

opt -instcombine

define i64 @rotvar(i64 %a0, i64 %a1, i64 %a2) {
  %1 = tail call i64 @llvm.fshl.i64(i64 %a0, i64 %a0, i64 %a2)
  ret i64 %1
}

define i64 @fshvar(i64 %a0, i64 %a1, i64 %a2) {
  %m = and i64 %a2, 63
  %n = sub i64 0, %a2
  %s = and i64 %n, 63
  %1 = shl i64 %a0, %m
  %2 = lshr i64 %a1, %s
  %3 = or i64 %1, %2
  ret i64 %3
}

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