[FIRRTL][LowerLayers] Lower layers does not update HPs of non-local annotations

[youngar]

Given this firrtl IR:

FIRRTL version 4.0.0
circuit Top: %[[ {"class": "circt.test", "target": "~Top|Top/foo:Foo>w"} ]]
  layer A, bind:

  public module Top:
    inst foo of Foo
    inst bar of Foo
  module Foo:
    layerblock A:
      wire w : UInt<8>
      invalidate w

compiling with firtool -parse-only test.fir gives the following IR:

module {
  firrtl.circuit "Top" {
    hw.hierpath private @nla [@Top::@sym, @Foo]
    firrtl.layer @A  bind {
    }
    firrtl.module @Top() attributes {convention = #firrtl<convention scalarized>} {
      firrtl.instance foo sym @sym interesting_name @Foo()
      firrtl.instance bar interesting_name @Foo()
    }
    firrtl.module private @Foo() {
      firrtl.layerblock @A {
        %w = firrtl.wire interesting_name {annotations = [{circt.nonlocal = @nla, class = "circt.test"}]} : !firrtl.uint<8>
        %invalid_ui8 = firrtl.invalidvalue : !firrtl.uint<8>
        firrtl.matchingconnect %w, %invalid_ui8 : !firrtl.uint<8>
      }
    }
  }
}

After LowerLayers runs we get this IR:

// -----// IR Dump After LowerLayers (firrtl-lower-layers) //----- //
firrtl.circuit "Top" {
  sv.verbatim "`ifndef layers_Top_A\0A`define layers_Top_A" {output_file = #hw.output_file<"layers_Top_A.sv", excludeFromFileList>}
  hw.hierpath private @nla [@Top::@sym, @Foo]
  firrtl.module @Top() attributes {convention = #firrtl<convention scalarized>} {
    firrtl.instance foo sym @sym @Foo()
    firrtl.instance bar @Foo()
  }
  firrtl.module private @Foo_A() {
    %w = firrtl.wire {annotations = [{circt.nonlocal = @nla, class = "circt.test"}]} : !firrtl.uint<8>
    %c0_ui8 = firrtl.constant 0 : !firrtl.uint<8>
    firrtl.matchingconnect %w, %c0_ui8 : !firrtl.uint<8>
  }
  firrtl.module private @Foo() {
    firrtl.instance a {lowerToBind, output_file = #hw.output_file<"layers_Top_A.sv", excludeFromFileList>} @Foo_A()
  }
  sv.verbatim "`endif // layers_Top_A" {output_file = #hw.output_file<"layers_Top_A.sv", excludeFromFileList>}
}

This issue is that the non-local annotation on wire w is not updated when the wire is moved in to a module Foo_A, and corresponding hierpath operation still points to @Foo. I.e. hw.hierpath private @nla [@Top::@sym, @Foo] should be hw.hierpath private @nla [@Top::@sym, @Foo::@a_sym, @Foo_A] and the instance of Foo_A needs a new symbol a_sym.

Note that we can't just modify the original HierpathOp, since it may have other users which were not moved, so we must create a new Hierpath op.

This currently does not trigger a verifier error, which has a tracking issue here: https://github.com/llvm/circt/issues/4896 A similar issue was tackled here: https://github.com/llvm/circt/issues/6717