edit: Thanks, I just checked and the warning doesn't work https://godbolt.org/z/...

edit: Thanks, I just checked and the warning doesn't work

But your hint found -fno-delete-null-pointer-checks which does the trick

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

And -fno-delete-null-pointer-checks made it into LLVM too. It's a good to know but a little late for when I needed it, cheers :)

  % cc -O3 -fno-delete-null-pointer-checks -Wall -Wextra -c foo.c
  % objdump -dr foo.o                                            
  
  foo.o: file format Mach-O 64-bit x86-64
  
  
  Disassembly of section __TEXT,__text:
  
  0000000000000000 _foo:
         0: 55                            pushq %rbp
         1: 48 89 e5                      movq %rsp, %rbp
         4: 48 85 ff                      testq %rdi, %rdi
         7: 74 04                         je 4 <_foo+0xd>
         9: 8b 07                         movl (%rdi), %eax
         b: 5d                            popq %rbp
         c: c3                            retq
         d: bf 02 00 00 00                movl $2, %edi
        12: e8 00 00 00 00                callq 0 <_foo+0x17>
    0000000000000013:  X86_64_RELOC_BRANCH _exit