> Date: Sat, 19 Jun 2021 16:40:08 +0100
> From: Dmitrii Pasechnik <dima.pasech...@cs.ox.ac.uk>
> Cc: bo...@kolpackov.net, bug-make <bug-make@gnu.org>
> Compiler does not guarantee you that doing something with p[-1]
> is not going to end in a segfault. It's hack, as it just happens to work, but 
> E.g. clang 10, or Apple's clang 12, will print a warning:
> warning: array index -1 is before the beginning of the array [-Warray-bounds]
> printf("%d", p[-1]);
>              ^ ~~

That warning is a bug in the compiler.  p is not an array, it's a
pointer into an array, and it doesn't have to (and in this case
actually does not) point to the first element of that array.

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