[sigjuice]

Compiler warnings are not straightforward and depend on many things; compiler version, optimization settings, warning settings.

  $ gcc-9 -Wuninitialized -O0 float.c  # NO WARNINGS!!!

  $ gcc-9 -O1 float.c  # NO WARNINGS!!!
  
  $ gcc-9 -Wuninitialized -O1 float.c
  float.c: In function 'main':
  float.c:9:5: warning: 'i' is used uninitialized in this function [-Wuninitialized]
      9 |     for (size_t i; i < (1ul << 33); i++) {
        |     ^~~

[piadodjanho]

Weirdly, those two codes behaves differently:

    $ gcc hn.c -O0 -o hn

    for (size_t i; i < (1ul<<46); i++) {
        printf ("%zd\n",i);
        acc += x;
        break;
    }

Without break:

    $ gcc hn.c -O0 -o hn

    for (size_t i; i < (1ul<<46); i++) {
        printf ("%zd\n",i);
        acc += x;
    }