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For what it's worth, with current HEAD of master (commit 62be33870e2f8517314bf9c7275548e799296f7e which includes previously merged PRs from this issue), current macOS clang with address sanitizer and pydebug enabled gets an assertion failure in parsetok.c. Current HEAD of 3.7 does not.
$ ./configure --with-address-sanitizer --prefix=/tmp/d --with-pydebu
$ make -j3
[...]
./python -E -S -m sysconfig --generate-posix-vars ;\
	if test $? -ne 0 ; then \
		echo "generate-posix-vars failed" ; \
		rm -f ./pybuilddir.txt ; \
		exit 1 ; \
	fi
 CC='gcc' LDSHARED='gcc -bundle -undefined dynamic_lookup -fsanitize=address ' OPT='-g -O0 -Wall' 	_TCLTK_INCLUDES='' _TCLTK_LIBS='' 	./python -E ./setup.py build
Assertion failed: ((intptr_t)(int)(a - line_start) == (a - line_start)), function parsetok, file Parser/parsetok.c, line 308.
/bin/sh: line 1: 95059 Abort trap: 6 CC='gcc' LDSHARED='gcc -bundle -undefined dynamic_lookup -fsanitize=address ' OPT='-g -O0 -Wall' _TCLTK_INCLUDES='' _TCLTK_LIBS='' ./python -E ./setup.py $quiet build
make: *** [sharedmods] Error 134
$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-10001145.5)
Target: x86_64-apple-darwin18.2.0
Thread model: posix
# same result with explicit CC=clang