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computing the program properties involved to the new settings and paradigms
of interest.
In this article we will reconsider optimization under the perspective of sound-
ness, completeness, and reusability on both the transformation and the analysis
level. We will illustrate this approach considering PRE as running example. By
means of the placing strategy underlying the SE-transformation we will par-
ticularly demonstrate that the rationale guaranteeing the soundness and com-
pleteness of an optimization for a specic setting is usually quite sensitive to
paradigm changes. Neither completeness nor even soundness are generally pre-
served. This shows that the reuse of optimization strategies in advanced settings
and paradigms requires typically paradigm-specic adaptations. In particular, it
demonstrates that the successful extension of the analyses computing the pro-
gram properties involved in a transformation like safety and earliestness for the
example of the SE-transformation is necessary to reuse an optimization strategy,
but generally not sucient. We will exemplify this for PRE, and demonstrate
that paradigm-specic adaptations are generally worth the eort. They yield an
eective contribution to the challenge of mastering the complexity of compiler
construction in the specic eld of code optimization.
a)
b)
a := ...
Ins
a := ...
x := a+b
Rpl
Ins
Rpl
z := a+b
x := a+b
z := a+b
Rpl
Rpl
Rpl
b := a+b
Data-flow Information
Up-safe Points
Down-safe Points
Insertions (Ins) and Replacements (Rpl)
Safety = Up-safety + Down-safety
=
+
Fig. 2. Illustrating the essence of computationally optimal code motion.
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