[junke]

What is the meaning of use(*p) in case p is null? what should the compiler emit?

[a1369209993]

> What is the meaning of use(*p) in case p is null?

It dereferences a null pointer, invoking undefined behaviour, then calls the function `use` with the resulting value.

> what should the compiler emit?

Probably something to the effect of:

  ld r0 [sp+.p]  # if p is not already in a register
  ld r0 [r0]  # *p
  jsr use

but it would be fine to emit something like:

  ld r0 [sp+.p]  # if p is not already in a register
  jz r0 .panic
  ld r0 [r0]  # *p
  jsr use

because the jz can only be taken when undefined behaviour happens.

[leosarev]

If p is statically null, it should emit compile time error. If not, it should emit machine instruction to deference p.

[tom_mellior]

In all of the examples above it will emit a machine instruction to dereference p. What your grandparent is complaining about is that it will later remove an "if (!p)" test.