[LLVMdev] Floating point atomic load and add

[Tim Northover]

> Hmm, ok. Can you briefly expand on how I should emulate this behavior? I
> don't understand what you mean by adding a loop around cmpxchg.

Probably easiest to write down in C:

#include <stdatomic.h>
void foo(_Atomic(float) *addr, float increment) {
  float oldval = *addr, newval;
  do {
    newval = oldval + increment;
  } while (__c11_atomic_compare_exchange_weak(
      addr, &oldval, newval, memory_order_seq_cst, memory_order_relaxed));
}

Basically you keep trying to just swap in the new value until you've
managed to do it atomically (or possibly with an intervening ABA
change, but that doesn't matter usually).

Tim.