CSE Doesn't Merge Source Locators

I've noticed that CSE doesn't seem to merge source locators. E.g., in the following, the source locator on the second add gets dropped:

circuit Foo:
  module Foo:
    input a: UInt<1>
    input b: UInt<1>

    node x = add(a, b)
    node y = add(a, b)

Running with circt-translate -import-firrtl cse.fir | circt-opt -cse -mlir-print-debuginfo -mlir-print-ir-after-all -mlir-print-ir-before-all produces:

// -----// IR Dump Before CSE (cse) //----- //
module {
  firrtl.circuit "Foo"  {
    firrtl.module @Foo(in %a: !firrtl.uint<1>, in %b: !firrtl.uint<1>) {
      %0 = firrtl.add %a, %b : (!firrtl.uint<1>, !firrtl.uint<1>) -> !firrtl.uint<2> loc(#loc3)
      %x = firrtl.node interesting_name %0  : !firrtl.uint<2> loc(#loc4)
      %1 = firrtl.add %a, %b : (!firrtl.uint<1>, !firrtl.uint<1>) -> !firrtl.uint<2> loc(#loc5)
      %y = firrtl.node interesting_name %1  : !firrtl.uint<2> loc(#loc6)
    } loc(#loc2)
  } loc(#loc1)
} loc(#loc)
#loc = loc("<stdin>":1:1)
#loc1 = loc("<stdin>":2:3)
#loc2 = loc("<stdin>":3:5)
#loc3 = loc("<stdin>":4:12)
#loc4 = loc("<stdin>":5:12)
#loc5 = loc("<stdin>":6:12)
#loc6 = loc("<stdin>":7:12)

// -----// IR Dump After CSE (cse) //----- //
module {
  firrtl.circuit "Foo"  {
    firrtl.module @Foo(in %a: !firrtl.uint<1>, in %b: !firrtl.uint<1>) {
      %0 = firrtl.add %a, %b : (!firrtl.uint<1>, !firrtl.uint<1>) -> !firrtl.uint<2> loc(#loc3)
      %x = firrtl.node interesting_name %0  : !firrtl.uint<2> loc(#loc4)
      %y = firrtl.node interesting_name %0  : !firrtl.uint<2> loc(#loc5)
    } loc(#loc2)
  } loc(#loc1)
} loc(#loc)
#loc = loc("<stdin>":1:1)
#loc1 = loc("<stdin>":2:3)
#loc2 = loc("<stdin>":3:5)
#loc3 = loc("<stdin>":4:12)
#loc4 = loc("<stdin>":5:12)
#loc5 = loc("<stdin>":7:12)

module {
  firrtl.circuit "Foo"  {
    firrtl.module @Foo(in %a: !firrtl.uint<1>, in %b: !firrtl.uint<1>) {
      %0 = firrtl.add %a, %b : (!firrtl.uint<1>, !firrtl.uint<1>) -> !firrtl.uint<2> loc(#loc3)
      %x = firrtl.node interesting_name %0  : !firrtl.uint<2> loc(#loc4)
      %y = firrtl.node interesting_name %0  : !firrtl.uint<2> loc(#loc5)
    } loc(#loc2)
  } loc(#loc1)
} loc(#loc)
#loc = loc("<stdin>":1:1)
#loc1 = loc("<stdin>":2:3)
#loc2 = loc("<stdin>":3:5)
#loc3 = loc("<stdin>":4:12)
#loc4 = loc("<stdin>":5:12)
#loc5 = loc("<stdin>":7:12)

I would expect to see the original #loc5 (:6:12) to be merged with #loc3, but it instead is dropped. This may be an MLIR limitation.

llvm / circt

CSE Doesn't Merge Source Locators #4358