[issue43760] The DISPATCH() macro is not as efficient as it could be (move PyThreadState.use_tracing)

[Pablo Galindo Salgado]

Pablo Galindo Salgado <pablogsal at gmail.com> added the comment:

>From PR 28498:

@vstinner @ambv The ABI is not broken, the only thing that this PR change is the size of the struct. All the offsets to the members are the same and therefore will be valid in any compiled code.

Any compiled wheels will still work. Look at the ABI report:

  [C]'function void PyEval_AcquireThread(PyThreadState*)' at ceval.c:447:1 has some indirect sub-type changes:
    parameter 1 of type 'PyThreadState*' has sub-type changes:
      in pointed to type 'typedef PyThreadState' at pystate.h:20:1:
        underlying type 'struct _ts' at pystate.h:62:1 changed:
          type size changed from 2240 to 2304 (in bits)
          1 data member insertion:
            'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
          1 data member changes (2 filtered):
           type of 'PyInterpreterState* _ts::interp' changed:
             in pointed to type 'typedef PyInterpreterState' at pystate.h:22:1:
               underlying type 'struct _is' at pycore_interp.h:220:1 changed:
                 type size hasn't changed
                 1 data member changes (3 filtered):
                  type of '_PyFrameEvalFunction _is::eval_frame' changed:
                    underlying type 'PyObject* (PyThreadState*, PyFrameObject*, int)*' changed:
                      in pointed to type 'function type PyObject* (PyThreadState*, PyFrameObject*, int)':
                        parameter 1 of type 'PyThreadState*' has sub-type changes:
                          in pointed to type 'typedef PyThreadState' at pystate.h:20:1:
                            underlying type 'struct _ts' at pystate.h:62:1 changed:
                              type size changed from 2240 to 2304 (in bits)
                              1 data member insertion:
                                'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
                              1 data member changes (2 filtered):
                               type of '_ts* _ts::next' changed:
                                 in pointed to type 'struct _ts' at pystate.h:62:1:
                                   type size changed from 2240 to 2304 (in bits)
                                   1 data member insertion:
                                     'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
                                   no data member changes (2 filtered);




  [C]'function PyThreadState* PyGILState_GetThisThreadState()' at pystate.c:1455:1 has some indirect sub-type changes:
    return type changed:
      in pointed to type 'typedef PyThreadState' at pystate.h:20:1:
        underlying type 'struct _ts' at pystate.h:62:1 changed:
          type size changed from 2240 to 2304 (in bits)
          1 data member insertion:
            'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
          no data member changes (4 filtered);

  [C]'function int _PyErr_CheckSignalsTstate(PyThreadState*)' at signalmodule.c:1767:1 has some indirect sub-type changes:
    parameter 1 of type 'PyThreadState*' has sub-type changes:
      in pointed to type 'typedef PyThreadState' at pystate.h:20:1:
        underlying type 'struct _ts' at pystate.h:62:1 changed:
          type size changed from 2240 to 2304 (in bits)
          1 data member insertion:
            'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
          no data member changes (3 filtered);

  [C]'function void _PyErr_Clear(PyThreadState*)' at errors.c:453:1 has some indirect sub-type changes:
    parameter 1 of type 'PyThreadState*' has sub-type changes:
      in pointed to type 'typedef PyThreadState' at pystate.h:20:1:
        underlying type 'struct _ts' at pystate.h:62:1 changed:
          type size changed from 2240 to 2304 (in bits)
          1 data member insertion:
            'int _ts::use_tracing', at offset 2240 (in bits) at pystate.h:151:1
          no data member changes (3 filtered);
As you can see, the leaves of the change is only type size changed from 2240 to 2304. As the member is added

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<https://bugs.python.org/issue43760>
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