DMS Software Reengineering Toolkit: Difference between revisions

Revision as of 02:27, 27 July 2011

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DMS provides attribute evaluators for computing custom analyses over ASTs, such as metrics, and including special support for [[symbol table]] construction. Other program facts can be extracted by built-in control- and data- [[flow analysis]] engines, local and global [[pointer analysis]], whole-program [[call graph]] extraction, and symbolic range analysis by [[abstract interpretation]].

Changes to ASTs can be accomplished by both procedural methods coded in PARLANSE and rulesource-driven surfaceto-syntaxsource tree transformations, coded as rewrite rules using surface-syntax conditioned by any of the extracted program facts. The rewrite rule engine handles associative and commutative rules. A rewrite rule for C to replace a complex condition by the '''?:''' operator be written as:

rule simplify_conditional_assignment(v:left_hand_side,e1:expression,e2:expression)

:statement->statement

= " if (\e1) \v=\e2; else \v=e3; "

-> " \v=\e1:?\e2:\e3; "

if no_side_effects(v);

Rewrite '''rule'''s have names, e.g. '''simplify_conditional_assignment'''. Each rule has a ''"match this"'' and ''"replace by that"'' pattern pair separated by '''->''', in our example, on separate lines for readability. The patterns must correspond to language syntax categories; in this case, both patterns must be of syntax category '''statement''' also separated in sympathy with the patterns by '''->'''. Target language (e.g., C) surface synax is coded inside meta-quotes '''"''', to separate rewrite-rule syntax from that of the target language. Backslashes inside meta-quotes represent ___domain escapes, to indicate pattern meta variables (e.g., '''\v''', '''\e1''', '''\e2''') that match any language construct corresponding to the metavariable declaration in the signature line, e.g., '''e1''' must be of syntactic category: ''(any) expression''. If a metavariable is mentioned multiple times in the ''match'' pattern, it must match to identical subtrees; the same identically shaped '''v''' must occur in both assignments in the match pattern in this example. Metavariables in the ''replace'' pattern are replaced by the corresponding matches from the left side. A conditional clause '''if''' provides an additional condition that must be met for the rule to apply, e.g., that the matched metavariable '''v''', being an arbitrary left-hand side, must not have a side effect (e.g., cannot be of the form of '''a[i++]'''; the '''no_side_effects''' predicate is defined by an analyzer built with other DMS mechanisms).

Achieving a complex transformation on code is accomplished by providing a number of rules that cooperate to achieve the desired effect. The ruleset is focused on portions of the program by metaprograms coded in PARLANSE.

A [http://www.semanticdesigns.com/Products/DMS/SimpleDMSDomainExample.html complete example] of a language definition and source-to-source transformation rules defined and applied is shown using high school [[algebra]] and a bit of [[calculus]] as a ___domain-specific language.

ItDMS has a variety of predefined language front ends, covering most real dialects of [[C (programming language)|C]] and [[C++]] including [[C++0x]], [[C Sharp (programming language)|C#]], [[Java (programming language)|Java]], [[Python (programming language)|Python]], [[PHP]], [[EGL (programming language)| EGL]], [[Fortran]], [[COBOL]], [[Visual Basic]], [[Verilog]], [[VHDL]] and some 20 or more other languages. Predefined languages enable customizers to immediately focus on their reengineering task rather than on the details of the languages to be processed.

DMS is additionally unusual in being implemented in a [[parallel programming]] language, PARLANSE, that uses [[symmetric multiprocessor]]s available on commodity [[workstations]]. This enables DMS to provide faster answers for large system analyses and conversions.