3.12: segmentation fault from compile() builtin

Crash report

I can trigger a crash of the 3.12 interpreter using the following Python instruction:

compile("assert (False if 1 else True)", "<string>", "exec")

Error messages

The full output when running locally-built cpython with debug assertions avoids a segfault, triggering an assertion instead:

$ ./python
Python 3.12.0a2+ (heads/main:f1a4a6a587, Nov 22 2022, 22:12:33) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> compile("assert (False if 1 else True)", "<string>", "exec")
python: Python/compile.c:8703: remove_redundant_jumps: Assertion `no_empty_basic_blocks(g)' failed.
Aborted

Your environment

I originally encountered the segmentation fault on macOS with 3.12.0a1.

I have reproduced it above with f1a4a6a on ubuntu (inside WSL).

Linked PRs

gh-99708: fix bug where compiler crashes on if expression with an empty body block #99732

@iritkatriel

cc @iritkatriel

Thanks for the report. This is not only with exceptions, seems to be empty exit block with a const-False if condition:

% ./python.exe -c "compile('def f():\n\tif not (False if 1 else True): return 12', 'file', 'exec')"
Assertion failed: (no_empty_basic_blocks(g)), function remove_redundant_jumps, file compile.c, line 8691.
zsh: abort      ./python.exe -c 
% ./python.exe -c "compile('def f():\n\tif not (False if 1 else True): xyz = 123', 'file', 'exec')"
% ./python.exe -c "compile('def f():\n\tif not (False if 1 else True):\n\t\txyz = 123\n\t\treturn 42', 'file', 'exec')"
%

A newline seems to make a difference:

% ./python.exe -c "compile('def f():\n\tif not (False if 1 else True): return 12', 'file', 'exec')"
Assertion failed: (no_empty_basic_blocks(g)), function remove_redundant_jumps, file compile.c, line 8691.
zsh: abort      ./python.exe -c 
% ./python.exe -c "compile('def f():\n\tif not (False if 1 else True):\n\t return 12', 'file', 'exec')"
%

A newline seems to make a difference

That's because we add a NOP for the line of the dead code, so the block is not empty.

pythongh-99708: fix bug where compiler crashes on if expression with …

gh-99708: fix bug where compiler crashes on if expression with an emp…

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3.12: segmentation fault from compile() builtin #99708

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3.12: segmentation fault from compile() builtin #99708

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corona10 commented on Nov 23, 2022

iritkatriel commented on Nov 23, 2022

iritkatriel commented on Nov 23, 2022

iritkatriel commented on Nov 23, 2022

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