Eliminate if updates
This CIF to CIF transformation eliminates 'if' updates on edges.
Supported specifications
This transformation supports a subset of CIF specifications. The following restrictions apply:
Multi-assignments and partial variable assignments are not supported. That is, the left hand sides of the assignments on edges (the addressables) must be single variables without projections.
Preprocessing
No preprocessing, to increase the subset of CIF specifications that can be transformed, is currently performed by this CIF to CIF transformation.
Implementation details
This transformation ensures that each variable that is assigned, gets a single explicit assignment. Simply put, the 'if' update structure is replicated by an 'if' expression. For instance, the following edge updates:
if g:
if g2:
x := 5
else
y := 6
end
end,
z := 7are transformed to the following edge updates:
x := if g:
if g2:
5
else
x
end
else
x
end,
y := if g:
if g2:
y
else
6
end
else
y
end,
z := 7Observe how variables x and y are assigned inside two if updates. These if updates are replicated by two if expressions.
Since for if expressions the else part is not optional, dummy x := x assignments are sometimes performed in cases where the original specification would not have assigned variable x at all. That is, variables may be assigned their old values, resulting in superfluous assignments.
Size considerations
The 'if' structure may be replicated for multiple variables, which may result in an increase of the specification size. The increase amount is influenced by the size of the guard expressions, and the number of levels of nesting 'if' updates.
Optimality
The superfluous assignments (see the Implementation details section above), are obviously not optimal. The language however requires them.