early block return retains $! filling cause for next error

[kares]

def raise_rescue!
  [ 1 ].each do # removing block gets cause to be nil
    begin
      raise StandardError.new("err")
    rescue => e
      puts("ERROR #{e.object_id} #{e.cause ? print_cause(e) : 'nil cause'}")
      return # problematic 'early' return
    end
  end
end

def print_cause(e)
  cause = e.cause
  "cause: #{cause.object_id} #{cause.cause && print_cause(cause)}"
end

3.times do
  raise_rescue!
end

expected: like MRI 3x nil cause

ERROR 47192120218900 nil cause
ERROR 47192120217920 nil cause
ERROR 47192120217540 nil cause

actual:

jruby 9.2.10.0-SNAPSHOT (2.5.7) 2019-12-31 fe4b188 Java HotSpot(TM) 64-Bit Server VM 11.0.2+9-LTS on 11.0.2+9-LTS +jit [linux-x86_64]
ERROR 2000 nil cause
ERROR 2002 cause: 2000 
ERROR 2004 cause: 2002 cause: 2000 

[headius]

Ok I expect this is due to the non-local return here not clearing $!. Note that the put_global_var for $! does not appear in the non-local return logic in the second output below (from ip 19 on).

Here's IR for a return inside rescue in a normal method body:

begin INSTANCE_METHOD<foo>
flags: [FLAGS_COMPUTED]
signature(pre=0,opt=0,post=0,rest=NONE,kwargs=0,kwreq=0,kwrest=-1)

  00:           %self := recv_self
  01:            %v_0 := load_implicit_closure
  02:  %current_scope := copy(scope<>)
  03: %current_module := copy(mod<0>)
  04:                    check_arity(required: 0, opt: 0, rest: false, receivesKeywords: false, restKey: -1)
  05:            %v_3 := get_global_var($<$!>)
  06:                    label(ipc<LBL_0:7>)
  07:                    exc_region_start(ipc<LBL_3:29>)
  08:                    label(ipc<LBL_4:9>)
  09:                    exc_region_start(ipc<LBL_5:18>)
  10:                    toggle_backtrace(requiresBacktrace: true)
  11:                    line_num(lineNumber: 0)
  12:            %v_6 := call_0o(self<%self>, callType: VARIABLE, name: bar, potentiallyRefined: false)
  13:                    exc_region_end
  14:            %v_5 := copy(%v_6)
  15:                    put_global_var($<$!>, %v_3, operand1: $!, operand2: %v_3)
  16:                    jump(ipc<LBL_2:32>)
  17:                    label(ipc<LBL_5:18>)
  18:            %v_7 := recv_ruby_exc
  19:            %v_8 := rescue_eqq(stderr<>, %v_7)
  20:                    b_true(ipc<LBL_7:24>, %v_8, jumpTarget: LBL_7:24, value: %v_8)
  21:                    label(ipc<LBL_6:22>)
  22:                    throw(%v_7)
  23:                    label(ipc<LBL_7:24>)
  24:            %v_9 := copy(nil<>)
  25:                    put_global_var($<$!>, %v_3, operand1: $!, operand2: %v_3)
  26:                    return(%v_9)
  27:                    exc_region_end
  28:                    label(ipc<LBL_3:29>)
  29:           %v_10 := recv_jruby_exc
  30:                    throw(%v_10)
  31:                    label(ipc<LBL_2:32>)
  32:                    return(%v_5)

And for within a block:

begin CLOSURE<_CLOSURE_1>
flags: [HAS_NONLOCAL_RETURNS, REQUIRES_DYNSCOPE, REQUIRES_BLOCK, FLAGS_COMPUTED]
signature(pre=0,opt=0,post=0,rest=NONE,kwargs=0,kwreq=0,kwrest=-1)

  00:                    exc_region_start(ipc<_GLOBAL_ENSURE_BLOCK__0:34>)
  01:           %self := recv_self
  02:         %cl_1_0 := load_frame_closure
  03:  %current_scope := copy(scope<>)
  04: %current_module := copy(mod<0>)
  05:                    line_num(lineNumber: 0)
  06:         %cl_1_3 := get_global_var($<$!>)
  07:                    label(ipc<CL1_LBL_0:8>)
  08:                    exc_region_start(ipc<CL1_LBL_3:28>)
  09:                    label(ipc<CL1_LBL_4:10>)
  10:                    exc_region_start(ipc<CL1_LBL_5:18>)
  11:                    toggle_backtrace(requiresBacktrace: true)
  12:         %cl_1_6 := call_0o(self<%self>, callType: VARIABLE, name: bar, potentiallyRefined: false)
  13:                    exc_region_end
  14:         %cl_1_5 := copy(%cl_1_6)
  15:                    put_global_var($<$!>, %cl_1_3, operand1: $!, operand2: %cl_1_3)
  16:                    jump(ipc<CL1_LBL_2:31>)
  17:                    label(ipc<CL1_LBL_5:18>)
  18:         %cl_1_7 := recv_ruby_exc
  19:         %cl_1_8 := rescue_eqq(stderr<>, %cl_1_7)
  20:                    b_true(ipc<CL1_LBL_7:24>, %cl_1_8, jumpTarget: CL1_LBL_7:24, value: %cl_1_8)
  21:                    label(ipc<CL1_LBL_6:22>)
  22:                    throw(%cl_1_7)
  23:                    label(ipc<CL1_LBL_7:24>)
  24:                    check_for_lje(definedWithinMethod: false)
  25:                    nonlocal_return(nil<>, methodId: --none--)
  26:                    exc_region_end
  27:                    label(ipc<CL1_LBL_3:28>)
  28:         %cl_1_9 := recv_jruby_exc
  29:                    throw(%cl_1_9)
  30:                    label(ipc<CL1_LBL_2:31>)
  31:                    return(%cl_1_5)
  32:                    exc_region_end
  33:                    label(ipc<_GLOBAL_ENSURE_BLOCK__0:34>)
  34:        %cl_1_10 := recv_jruby_exc
  35:        %cl_1_11 := runtime_helper(%cl_1_10, helperMethod: HANDLE_BREAK_AND_RETURNS_IN_LAMBDA)
  36:                    return_or_rethrow_saved_exc(%cl_1_11)
  37:                    label(ipc<CL1_LBL_8:38>)