No it couldn't, because the compiler cannot make assumptions about the heap allocator beyond what the C spec says, which is basically just the function signatur

No it couldn't, because the compiler cannot make assumptions about the heap allocator beyond what the C spec says, which is basically just the function signatures. An allocator that never frees memory is entirely within the C spec and would need not know individual allocated sizes after allocation. Or, if a compiler decided to anyway, it would have to link a compiler-specific standard library because it's entirely implementation-dependant what and where bookkeeping information is stored. In turn, this means you couldn't safely link code compiled by different compilers. Bjarne might think that fine and dandy, but C never had that level of damage.