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saagarjha • today at 12:34 AM • 3 replies • view on HN

The problem is the code unconditionally dereferences the pointer, which would be UB if it was a null pointer. This means it is legal to optimize out any code paths that rely on this, even if they occur earlier in program order.

Replies

teo_zero • today at 7:23 AM

> it is legal to optimize out any code paths that rely on this, even if they occur earlier in program order.

I don't think this is true. The compiler cannot remove or reorder instructions that have a visible effect.

  if (p == 0)
    printf("Ready?\n");
  *p++;
The printf() can't be omitted.
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pwdisswordfishy • today at 6:44 AM

But if the assertion fails, the program is aborted before the pointer would have been dereferenced, making it not UB. This explanation is bogus.

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aw1621107 • today at 12:46 AM

> The problem is the code unconditionally dereferences the pointer, which would be UB if it was a null pointer.

Only when NDEBUG is defined, right?

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