[llvm-bugs] [Bug 38639] New: lowerVectorShuffleByMerging128BitLanes - Detected cycle in SelectionDAG

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38639

            Bug ID: 38639
           Summary: lowerVectorShuffleByMerging128BitLanes - Detected
                    cycle in SelectionDAG
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com,
                    douglas_yung at playstation.sony.com,
                    greg.bedwell at sony.com, llvm-bugs at lists.llvm.org

D41794 is causing this fuzz test regression:

define <8 x double> @test(<4 x double> %a, <4 x double> %b) {
  %1 = shufflevector <4 x double> %a, <4 x double> <double undef, double
0x3FEA435134576E1C, double 0x3FEA435134576E1C, double 0x3FEA435134576E1C>, <8 x
i32> <i32 6, i32 5, i32 2, i32 3, i32 5, i32 1, i32 3, i32 7>
  ret <8 x double> %1
}

llc -mcpu=btver2

Detected cycle in SelectionDAG
Offending node:
t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
  t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
    t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
      t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
        t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
          t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
            t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
              t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
                t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26
                  t27: v4f64 = vector_shuffle<0,5,2,7> t27, t26

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