[intro.execution] p12 does not specify how evaluations in a function's body are ordered with respect to what's sequenced after the function call

[xmh0511]

Full name of submitter (unless configured in github; will be published with the issue): Jim X

[intro.execution] p12 says:

For each

• function invocation,

F, each evaluation that does not occur within F but is evaluated on the same thread and as part of the same signal handler (if any) is either sequenced before all evaluations that occur within F or sequenced after all evaluations that occur within F;

This rule is intended to mean that an evaluation A not occurring within F that would be otherwise unsequenced with F is indeterminately sequenced with F, that is, A cannot overlap with F. However, this rule does not specify how the order is in the following example:

int value = 0;
void fun(){
  value = 1; // #1
}
int main(){
  fun(); // #2 
  value = 2; // #3
}

[intro.execution] p12 means that #1 and #3 are indeterminately sequenced. [intro.execution] p11 says:

When invoking a function f (whether or not the function is inline), every argument expression and the postfix expression designating f are sequenced before every precondition assertion of f ([dcl.contract.func]), which in turn are sequenced before every expression or statement in the body of f, which in turn are sequenced before every postcondition assertion of f.

This means #2 is sequenced before #1; however, it still doesn't contribute to how #1 and #3 are ordered. The issue also exists in the inter-threaded happens-before case, for example, the function call F happens before another evaluation A; however, we cannot infer how the evaluations in F's body and A are ordered.

Suggested Resolution: