Prior to this change LLVM would happily elide a call to any allocation
function and a call to any free function operating on the same unused
pointer. This can cause problems in some obscure cases, for example if
the body of operator::new can be inlined but the body of
operator::delete can't, as in this example from jyknight:
#include <stdlib.h> #include <stdio.h> int allocs = 0; void *operator new(size_t n) { allocs++; void *mem = malloc(n); if (!mem) abort(); return mem; } __attribute__((noinline)) void operator delete(void *mem) noexcept { allocs--; free(mem); } void deleteit(int*i) { delete i; } int main() { int*i = new int; deleteit(i); if (allocs != 0) printf("MEMORY LEAK! allocs: %d\n", allocs); }
This patch addresses the issue by introducing the concept of an
allocator function family and uses it to make sure that alloc/free
function pairs are only removed if they're in the same family.
The vec_malloc/vec_calloc/vec_realloc/vec_free functions look like they should be a distinct family.