DXC does not eliminate wave intrinsic calls even when the result is unused

Description
The wave intrinsics are kept in the final dxil but I would expect them to be removed by DCE.

Steps to Reproduce

https://shader-playground.timjones.io/350a97df5de025ead832c7054409a7aa

// dxc /T ps_6_0 t.hlsl
[RootSignature("")]
void main(int a : A) {
  (void)WaveReadLaneFirst(a);
}

Actual Behavior

The output of WaveReadLaneFirst is unused, but the intrinsic call is still there in the dxil.

define void @main() {
  %1 = call i32 @dx.op.loadInput.i32(i32 4, i32 0, i32 0, i8 0, i32 undef)  ; LoadInput(inputSigId,rowIndex,colIndex,gsVertexAxis)
  %2 = call i32 @dx.op.waveReadLaneFirst.i32(i32 118, i32 %1)  ; WaveReadLaneFirst(value)
  ret void
}

Environment

• DXC version Version: dxcompiler.dll: 1.6 - 1.6.2104.52 (e09a454eb); dxil.dll: 1.6(101.6.2104.33). Also repros on shader-playground with dxc trunc.
• Host Operating System Windows

Start by reproducing the shader from the Shader Playground link with DXC and inspect the generated DXIL. Trace how DXC applies dead-code elimination to the unused WaveReadLaneFirst call, then verify that the intrinsic is absent from the output while compilation still succeeds.