gh-88226: Emit TARGET labels in Python/ceval.c when debugging, even if computed gotos aren't enabled

[smontanaro]

This is an updated PR from the original one I submitted (in the before GitHub issues days).

Note: I am still acquainting myself with my new MacBook, so don't have quite the full suite of autoconf tools available. I was thus unable to generate configure from configure.ac. I manually editing configure instead.

• Issue: Define TARGET macro the same even when computed goto support is not enabled #88226

[smontanaro]

I messed up the reference to the issue number when creating the NEWS blurb. I entered "25949" instead of "88226" (I think that's the right number). I don't know if the generated blurb can simply be git mv ...'d or not.

[smontanaro]

I think I fixed this problem. I git rm'd the first blurb then ran blurb again.

[smontanaro]

One other thing. I'm confident this does the right thing. I ran these steps to verify that no warnings were issued for unused labels when compiling Python/ceval.o:

#!/bin/bash

./configure --without-pydebug --with-computed-gotos 2>&1 | egrep -v '^checking'
echo "Computed goto, Py_DEBUG disabled"
rm -f Python/ceval.o
make Python/ceval.o

./configure --with-pydebug --with-computed-gotos 2>&1 | egrep -v '^checking'
echo "Computed goto, Py_DEBUG enabled"
rm -f Python/ceval.o
make Python/ceval.o

./configure --with-pydebug --without-computed-gotos 2>&1 | egrep -v '^checking'
echo "Computed goto disabled, Py_DEBUG enabled"
rm -f Python/ceval.o
make Python/ceval.o

./configure --without-pydebug --without-computed-gotos 2>&1 | egrep -v '^checking'
echo "Computed goto disabled, Py_DEBUG disabled"
rm -f Python/ceval.o
make Python/ceval.o

[smontanaro]

Clang seems happy with the change as well.

[smontanaro]

This still spits out warnings when compiling Python/ceval.c on Windows. I haven't the slightest idea how to control for that, but I assume it must be possible. If you know how this is done, can you make a suggestion?

[serhiy-storchaka]

Disabling the warnings globally looks not good to me. It can lead to preserving unused labels in other parts of the code. Why not disable them locally, using compiler-specific pragmas? This is how we handle other types of warnings.

[smontanaro]

Disabling the warnings globally looks not good to me. It can lead to preserving unused labels in other parts of the code. Why not disable them locally, using compiler-specific pragmas? This is how we handle other types of warnings.

I wasn't aware this was possible. I'll take a look. Thanks.

[smontanaro]

Update... Thanks to @zooba and @mattip, the latest variation performs a more surgical suppression of the unused label warning. configure is no longer affected, and the TARGET_* labels are always defined, not just when Py_DEBUG is enabled.

[smontanaro]

@serhiy-storchaka Can you merge this when you have a moment? Thx...

[serhiy-storchaka]

@smontanaro Aren't you a coredev? Don't you have the ability to do that yourself? I just don't promise that I will do it quickly, because we have regular blackouts here (5 minutes until the next blackout). But I will do it in 2 hours or tomorrow.

[smontanaro]

@serhiy-storchaka No worries and no rush, just as long as it's on your radar screen. Whenever you have a chance. I gave up my commit privilege a few years ago (don't really want it back).

I wasn't aware you are in Ukraine. Stay well.

[serhiy-storchaka]

Done. Don't forget to remove the branch in your GitHub repository and in your local copy if you no longer need it.