[Bug tree-optimization/123374] [16 regression] elfutils: bogus warning when building debuginfod.cxx since r16-5258

[siddhesh at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123374

--- Comment #13 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
Took all of 24 hours to reduce and generated 4 cvise bug reports in the
process, but here it is:

typedef struct {
  unsigned header_size;
} lzma_block;
long __read_alias(int, void *, unsigned long)
    __attribute__((__access__(__write_only__, 2, 3)));
int read___fd;
long read(void *__buf, long __nbytes) {
  long __trans_tmp_1 = __builtin_dynamic_object_size(__buf, 0);
  return __builtin_constant_p(__trans_tmp_1) &&
                 __trans_tmp_1 == (long)-1
             ? __read_alias(read___fd, __buf, __nbytes)
             : 0;
}
struct defer_dtor {
  defer_dtor(lzma_block *, void(lzma_block *));
};
void free_lzma_block_filters(lzma_block *);
char extract_xz_blocks_into_fd_in_buf[4096];
long extract_xz_blocks_into_fd_bytes_read;
void extract_xz_blocks_into_fd() {
  lzma_block block;
  defer_dtor(&block, free_lzma_block_filters);
  unsigned long header_read = 0;
  while (header_read == 0)
    header_read += extract_xz_blocks_into_fd_bytes_read;
  while (header_read < block.header_size) {
    long bytes_read =
        read(extract_xz_blocks_into_fd_in_buf + header_read,
             sizeof(extract_xz_blocks_into_fd_in_buf) - header_read);
    if (bytes_read)
      continue;
    header_read += bytes_read;
  }
}