https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95279
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Marc Glisse from comment #8) > (In reply to Jakub Jelinek from comment #4) > > There is nothing wrong on addition of -1, whether signed or cast to > > size_t/uintptr_t, to a pointer, > > Looking at the standard (I am not a pro at that), one could easily interpret > that p+(size_t)(-1) means adding a huge number to p, not subtracting 1. It > does not say that the integer is cast to ptrdiff_t or anything like that. I don't read it that way. Let's use e.g. the C++ wording: "Otherwise, if P points to an array element i of an array object x with n elements, the expressions P + J and J + P (where J has the value j) point to the (possibly-hypothetical) array element i+j of x if 0≤i+j≤n and the expression P - J points to the (possibly-hypothetical) array element i−j of x if 0≤i−j≤n. In the (#c4 testcase with the s/p + 1/buf + 1/ fix), i is 1, and j is either -1 or (size_t) -1. For both, 1 + -1 or 1 + (size_t) -1 give 0 and thus the pointer addition is well defined and points to the first element of the object.
