[jpatte]

From the article: "If the compiler/debugger is able to create this "evaluate every piece of line" format for functions (generating new ones when needed), then we can use the stack to check which branches we've taken — they're on the stack, after all!"

No, they are not. Having called functions instead of evaluating conditional statements doesn't change anything to the state of the [non-stale part of the] stack at the time you reach the breakpoint.

To achieve this one would need to execute the code following the branching (and containing the breakpoint) as callback of any of the "conditional" functions, so the followed branch would indeed appear in the stack. But that would just be impractical as you would reach stack overflow extremely quickly - not to mention the hit on performances.