_sre.c case is the most interesting one , compiler says :

./Modules/_sre.c:1002: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1069: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1086: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1143: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1185: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1214: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1238: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1251: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1277: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1291: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1308: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1395: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1408: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c: In function 'sre_umatch':
./Modules/_sre.c:1002: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1069: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1086: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1143: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1185: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1214: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1238: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1251: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1277: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1291: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1308: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1395: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1408: warning: assuming signed overflow does not occur
when simplifying conditional to constant

all lines refer to : RETURN_ON_ERROR(ret);

My investigation :

On line 1002 we got RETURN_ON_ERROR(ret); but ret is already 0 and not
set to anything this if will always be false.

Same for line 1069, ret is still zero there. Maybe I am missing
something here?