[InstSimplify] Simplify icmp between Shl instructions of the same value

define i1 @compare_vscales() {
  %vscale = call i64 @llvm.vscale.i64()
  %vscalex2 = shl nuw nsw i64 %vscale, 1
  %vscalex4 = shl nuw nsw i64 %vscale, 2
  %cmp = icmp ult i64 %vscalex2, %vscalex4
  ret i1 %cmp
}

This IR is currently emitted by LLVM. This icmp is redundant as this snippet
can be simplified to true or false as both operands originate from the same
@llvm.vscale.i64() call.

Differential Revision: https://reviews.llvm.org/D142542