[Octave-bug-tracker] [bug #64977] Explore options for the bytecode interpreter in Octave 9

[Petter]

Follow-up Comment #4, bug #64977 (project octave):

The incompatibility risk I am aware of is the computed goto:s in execute_code
() in pt-bytecode-vm.cc. I believe if compilation issues are the concern, #if
guards for the whole body of execute_code () should make compilers without
that GNU extension happy and if-guards around user facing functions that makes
no sense without being able to run the bytecode interpreter.

The bytecode interpreter is tested on 32-bit systems without problem, and
there is code to support big endian systems, but I have had no way to try that
on an actual big endian system.

I compiled with CXXFLAGS="-pedantic -std=c++17" and the complaints were:

./../libinterp/parse-tree/oct-parse.yy:417:53: warning: ISO C++11 requires at
least one argument for the "..." in a variadic macro
  417 |                     OCTAVE_YYUSE ($2);


./../liboctave/system/file-ops.cc: In function 'std::string
octave::sys::tempnam(const std::string&, const std::string&, std::string&)':
./../liboctave/system/file-ops.cc:752:8: warning: ISO C++ forbids variable
length array 'tname' [-Wvla]
  752 |   char tname [templatename.length () + 1];
|        ^~~~~

./../liboctave/util/oct-string.cc: In member function 'virtual int
octave::string::codecvt_u8::do_length(StateT&, const ExternT*, const ExternT*,
std::size_t) const':
./../liboctave/util/oct-string.cc:894:15: warning: ISO C++ forbids variable
length array 'offsets' [-Wvla]
  894 |   std::size_t offsets[srclen];
      |               ^~~~~~~


'pedantic' didn't trigger on the computed goto:s, so it does not seem to warn
on every GNU extension.

However I did find some function attributes I've missed guarding. I would
suggest something like the attached patch for those:

(file #55404)

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Additional Item Attachment:

File name: 32841.patch                    Size:2 KB
    <https://file.savannah.gnu.org/file/32841.patch?file_id=55404>



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