I'm NOT calling for the compiler to intentionally generate malicious code (that would be stupid, even if still conforming). I'm saying that it does NOT have to generate extra checks by default, nor refrain from optimising out useless ones, because this would not be in the spirit of C.
"deciding to 'optimize away' a check immediately afterwards that checks if the pointer is null (prior to the resulting variable being used) is not reasonable"
In the name of what?
You could abritrarily disallow a lot of optimisations with such edict.
Everybody that actually have read the C standard know that it perfectly allow such optimisation. See 220.127.116.11. See 18.104.22.168 (note)
Refraining from making optimisation just because it could make buggy program buggier is not reasonable. Just fix the buggy program. Or in some limited cases, explicitely use the flag that the GCC maintainers kindly provide you, so that even if your program is not strictly conforming, it remains conforming given this particular compiler and compilation option.