[3.14] gh-148284: Block inlining of gigantic functions in ceval.c for clang 22

[Fidget-Spinner]

It seems that on clang-22, the inliner is too aggressive on _PyEval_EvalFrameDefault when on computed goto interpreter. Together with some strange interaction with the stackref buffer, the function requires 40kB of stack space (!!!) versus the usual 1-2kB normally used.

This sets the inline limit to functions of max 512B stack space (1/4th of normal) allowed to be inlined in ceval.c. I checked the dissasembly and the new function uses about 2kB of stack.

This will need a forward-port to 3.15 too.

• Issue: python -m test -v test_call segfault with clang 22.1.3 build #148284

[vstinner]

This will need a forward-port to 3.15 too.

If possible, I would prefer to fix the main branch first, and then backport to 3.14.

[Fidget-Spinner]

If possible, I would prefer to fix the main branch first, and then backport to 3.14.

OK, I need to test on main first to see if there're issues there.

[vstinner]

Can you document this new variable in https://docs.python.org/dev/using/configure.html#envvar-CFLAGS_ALIASING ?

[Fidget-Spinner]

Is there a way to make this a private variable? I don't feel good exposing it for now.

[vstinner]

Reformat to 80 columns and minor cleanup:

Suggested change

	// See gh-148284:
	// Clang 22 seems to have interactions with inlining and the stackref buffer
	// which cause 40kB of stack usage on x86-64 in buggy versions of _PyEval_EvalFrameDefault
	// in computed goto interpreter. The normal usage seen is normally 1-2kB.
	// See gh-148284: Clang 22 seems to have interactions with inlining
	// and the stackref buffer which cause 40 kB of stack usage on x86-64
	// in buggy versions of _PyEval_EvalFrameDefault() in computed goto
	// interpreter. The normal usage seen is normally 1-2 kB.

[vstinner]

I suggest adding "Suppress inlining of functions whose stack size exceeds 512 bytes." to explain the purpose of this option:

Suggested change

	// This number should be tuned to follow the C stack consumption
	// in _PyEval_EvalFrameDefault on computed goto interpreter.
	// gh-148284: Suppress inlining of functions whose stack size exceeds
	// 512 bytes. This number should be tuned to follow the C stack
	// consumption in _PyEval_EvalFrameDefault() on computed goto
	// interpreter.

The Clang option is documented at: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-finline-max-stacksize

[vstinner]

In the past, when I tried to reduce the stack memory consumption on Python function calls, I used Py_NO_INLINE with success. But it seems harder to annotate functions used by ceval.c with Py_NO_INLINE, instead of the generic -finline-max-stacksize=512. I'm just a little bit worried that a similar issue occurs with other compilers (GCC, MSVC).

In ceval.c, I see that get_exception_handler() is already annotated with Py_NO_INLINE.

[Fidget-Spinner]

@vstinner PR moved to retarget main at #148334