What in assembly would allow freedom from false retention is that we know exactly what is in every register and memory location (because we put it there). We know where the GC has to look for root references and where it doesn't have to look.
In C, if we have a pointer p which is the last reference to some object, and is not used any more, and add the line "p = NULL", hoping to drop a reference so the object can be reclaimed, there is no guarantee that the compiler actually generates the code which does the assignment. Since the variable has no next use, and the compiler doesn't know anything about garbage collection, the assignment looks like wasteful, dead code that should be optimized away. Even if the scope finishes executing, the compiler can leave behind a memory location which still references the object.
Here is something else, not related to GC. In assembly language, we can make ourselves a calling convention for variadic functions which know how many arguments they have. As we build up the higher level language, it will have nicely featured variadic functions.
In C, we are stuck with <stdarg.h> which doesn't have a mechanism for the callee to know where the arguments end. The language has no flexibility to add this --- without resorting to approaches which will basically involve assembly language.
In C, if we have a pointer p which is the last reference to some object, and is not used any more, and add the line "p = NULL", hoping to drop a reference so the object can be reclaimed, there is no guarantee that the compiler actually generates the code which does the assignment. Since the variable has no next use, and the compiler doesn't know anything about garbage collection, the assignment looks like wasteful, dead code that should be optimized away. Even if the scope finishes executing, the compiler can leave behind a memory location which still references the object.
Here is something else, not related to GC. In assembly language, we can make ourselves a calling convention for variadic functions which know how many arguments they have. As we build up the higher level language, it will have nicely featured variadic functions.
In C, we are stuck with <stdarg.h> which doesn't have a mechanism for the callee to know where the arguments end. The language has no flexibility to add this --- without resorting to approaches which will basically involve assembly language.