I don't think that the mixing of definitions and statement has any effect on how the stack frame space is (re)used: even if all variable definitions are collect

I don't think that the mixing of definitions and statement has any effect on how the stack frame space is (re)used: even if all variable definitions are collected at the beginning of the block, it may still be possible for the compiler to find the points inside the block after which some of the variables are no longer used while some others are brought into action; such variables could, then, share the same space despite having the same lexical scope.