From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2026-09-23T04:10:47+00:00
Subject: [ruby-core:126834] [Ruby Bug#22377] compile.c: `getlocal` not turned into `getlocal_WC_0`

Issue #22377 has been updated by byroot (Jean Boussier).


Thanks for the repro, I think I know what's going on, I'll look into it.

----------------------------------------
Bug #22377: compile.c: `getlocal` not turned into `getlocal_WC_0`
https://bugs.ruby-lang.org/issues/22377#change-119178

* Author: alanwu (Alan Wu)
* Status: Open
* Backport: 3.3: DONTNEED, 3.4: DONTNEED, 4.0: DONTNEED
----------------------------------------
Missed by the "operands_unification" pass, somehow.
See 0023 below:

```text
   $ ./miniruby --parser=parse.y --dump=insns -e '
                assign = ->(outer) {
                  m = Module.new
                  m.set_temporary_name("m") # non-leaf call, so the next getlocal needs a patch point
                  outer::M = m
                  [m.name, outer::M.name]
                }'
   == disasm: #<ISeq:<main>@-e:1 (1,0)-(7,9)>
   local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
   [ 1] assign@0
   0000 putspecialobject                       1                         (   2)[Li]
   0002 send                                   <calldata!mid:lambda, argc:0, FCALL>, block in <main>
   0005 dup
   0006 setlocal_WC_0                          assign@0
   0008 leave
   
   == disasm: #<ISeq:block in <main>@-e:2 (2,17)-(7,9)>
   local table (size: 2, argc: 1 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
   [ 2] outer@0<AmbiguousArg>[ 1] m@1
   0000 putnil                                                           (   3)[LiBc]
   0001 opt_getconstant_path                   <ic:0 Module>
   0003 opt_new                                <calldata!mid:new, argc:0, ARGS_SIMPLE>, 10
   0006 opt_send_without_block                 <calldata!mid:initialize, argc:0, FCALL|ARGS_SIMPLE>
   0008 jump                                   13
   0010 opt_send_without_block                 <calldata!mid:new, argc:0, ARGS_SIMPLE>
   0012 swap
   0013 pop
   0014 setlocal_WC_0                          m@1
   0016 getlocal_WC_0                          m@1                       (   4)[Li]
   0018 dupchilledstring                       "m"
   0020 opt_send_without_block                 <calldata!mid:set_temporary_name, argc:1, ARGS_SIMPLE>
   0022 pop
*  0023 getlocal                               m@1, 0                    (   5)[Li]
   0026 getlocal_WC_0                          outer@0
   0028 setconstant                            :M
   0030 getlocal_WC_0                          m@1                       (   6)[Li]
   0032 opt_send_without_block                 <calldata!mid:name, argc:0, ARGS_SIMPLE>
   0034 getlocal_WC_0                          outer@0
   0036 putobject                              false
   0038 getconstant                            :M
   0040 opt_send_without_block                 <calldata!mid:name, argc:0, ARGS_SIMPLE>
   0042 newarray                               2
   0044 leave                                                            (   7)[Br]
```

Seems to only happen on trunk and not to be an issue on 4.0.x, 3.4.x, 3.3.x.
https://godbolt.org/z/TG9h1j37h

Seems to have started with commit:f4813a34c2 "compile.c: statically resolve `swap` instructions when possible" as its parent commit doesn't have this issue.

CC: @byroot 



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