PROGRAM STRUCTURE TREES - Software Systems Lab

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(a) Refined region
(b) After transformation
Figure 3: Transform an extended region to a plain region
Every region is also a refined region. The definitions for trivial and
canonical regions also apply to refined regions.
An analysis of the Polyhedron 1 benchmark showed that only about
30% of all refined regions are simple regions. The complete analysis
can be found in Table 2.
2.4 Program structure tree
In general there are multiple canonical regions in every CFG. Two
canonical regions A and B may contain the same basic blocks. In this
case either region A is completely contained in region B, such as all
basic blocks in A are also in B, or B is completely contained in A.
This relationship is represented as a program structure tree, where a
region B is an ancestor of A, if B is completely contained in A.
The example in 4 shows a CFG where the simple regions are marked
with blue and the refined regions with orange borders.
3 different algorithms
There are different algorithms available, that can be used to analyze a
CFG and build a region tree. They differ in the CFGs they can analyze,
the kind of region they can detect, as well as the implementation afford
necessary, the runtime complexity and/or the required prerequisites.
1 http://www.polyhedron.com
4