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kit
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opt_07_pointer_difference_index.c (580B)

      1 /* A same-width pointer-to-ptrdiff conversion may become a physical copy after
      2  * allocation.  Copy propagation may change the index register, but the
      3  * indirect use must retain its integer interpretation. */
      4 __attribute__((noinline)) static const char* pick(const char* base,
      5                                                   const char* tail,
      6                                                   char* copy) {
      7   return &base[tail - copy];
      8 }
      9 
     10 int test_main(void) {
     11   char base[] = "0123456789";
     12   char copy[] = "abcdefghij";
     13   return *pick(base, copy + 4, copy) == '4' ? 42 : 1;
     14 }