How stack frames look like when two functions lie in one line?

Question

For example, we have

int p(void) {
  return 4;
}

int q(void) {
  return 5;
}

int main(void) {
  int x = p() + q();
  return 0;
}

How does the stack frame look like in this case? To be exact, are p and q evaluated simultaneously, or after p is first evaluated to be 4, the program proceeds to q?

Answer 1

From cppreference

Order of evaluation of the operands of almost all C++ operators (including the order of evaluation of function arguments in a function-call expression and the order of evaluation of the subexpressions within any expression) is unspecified. The compiler can evaluate operands in any order, and may choose another order when the same expression is evaluated again.

There are exceptions to this rule which are noted below.

Except where noted below, there is no concept of left-to-right or right-to-left evaluation in C++. This is not to be confused with left-to-right and right-to-left associativity of operators: the expression f1() + f2() + f3() is parsed as (f1() + f2()) + f3() due to left-to-right associativity of operator+, but the function call to f3 may be evaluated first, last, or between f1() or f2() at run time