From: Paul Brannan <pbrannan@...>
Date: 2008-10-22T23:48:28+09:00
Subject: [ruby-core:19446] confused by this catch table

irb(main):001:0> require 'internal/proc'
=> true
irb(main):002:0> p = proc {
irb(main):003:1*   begin
irb(main):004:2*     1+1
irb(main):005:2>   rescue
irb(main):006:2>     2+2
irb(main):007:2>   end
irb(main):008:1> }
=> #<Proc:0x836aaa8@(irb):3>
irb(main):009:0> puts p.body.disasm
== disasm: <RubyVM::InstructionSequence:block (6 levels) in irb_binding@(irb)>
== catch table
| catch type: rescue st: 0002 ed: 0009 sp: 0000 cont: 0010
== disasm: <RubyVM::InstructionSequence:rescue in block (6 levels) in irb_binding@(irb)>
local table (size: 2, argc: 0 [opts: 0, rest: -1, post: 0, block: -1] s0)
[ 2] #$!
0000 putobject        StandardError                                   (   6)
0002 getdynamic       #$!, 0
0005 send             :===, 1, nil, 0, <ic>
0011 branchunless     21
0013 trace            1
0015 putobject        2
0017 putobject        2
0019 opt_plus
0020 leave
0021 getdynamic       #$!, 0
0024 throw            0
| catch type: retry  st: 0009 ed: 0010 sp: 0000 cont: 0002
| catch type: redo   st: 0000 ed: 0010 sp: 0000 cont: 0000
| catch type: next   st: 0000 ed: 0010 sp: 0000 cont: 0010
|------------------------------------------------------------------------
0000 trace            1                                               (   3)
0002 trace            1                                               (   4)
0004 putobject        1
0006 putobject        1
0008 opt_plus
0009 nop                                                              (   3)
0010 leave                                                            (   4)
=> nil

Given a start of 9 and an end of 10, the retry catch table entry seems
to cover only the instruction at address 9 (the nop).  So if a retry is
issued, how is it to have any effect?

(that is, since there is no code within the retry catch entry's
applicable instructions that can throw a retry tag, does this
effectively become a no-op?)

Paul