The Function and Structure of a Compiler

The Function and Structure of a Compiler

1. The function of a compiler

   • Implementation of a higher level virtual machine through translation rather than interpretation.
     • It is worth noting that in this sense 434 has a natural connection to 237 and 432. Together all these courses contribute to explaining how what you type as a line in a Java program ultimately turns into electrons flowing through a transistor.

   • Various forms compiler output can take:

     • machine code

     • object file

     • assembly language

     • C code, Java code

     • encoded form for interpretation (Java virtual machine code)

   • The fuzzy line between compilers and interpreters
2. The structure of a compiler

   • The BIG Picture

     

     The BIG PICTURE

   • General Roles of the Phases

     • Syntactic Analysis

       • Syntactic structure determines meaning.

         • Consider importance of recognition of syntactic structure in natural language ("time flies like an arrow." vs. "Fruit flies like an orchard.")

         • Consider an example from Java such as "Age[10]" which could either be part of a constructor ( add "new") or a reference to an array element
         • Consider the C code "(a) - b" which could be a strange way of writing a subtraction (if a and b are both of numeric types) or a cast of the result of the negation of the value of b to the type "a" (if a had been declared using "typedef a float;").

       • Syntactic analysis is the process of transforming a representation of a program as a sequence of characters into a representation in which the structure of program is explicit.

     • In most compilers, syntactic analysis is subdivided into two sub-phases:

       • Parsing: the process of grouping words and phrases into larger phrases of identifiable types.

       • Scanning: the process of grouping characters into "words". Scanning is also sometimes distinguished from syntactic analysis and called lexical analysis.

         It is hard to imagine that our brains don't have a similar separation that allows us to use the same mechanisms to parse a sentence whether we read it or hear it.

     • Semantic/Context sensitive Analysis

       • Observe that recognizing that the context in which the phrase `Age[10]' appears requires an expressions does not imply we know the "meaning" of the phrase. In fact, if `Age' is never declared or is a class name then the phrase is meaningless.

       • Semantic Analysis completes the internal representation of a program by processing declarations and verifying the legality of the program with regard to type and scoping rules.

       • Together, syntactic and semantic analysis enable the compiler to "understand" the source program.

     • Code Synthesis

       • Produces code from completed internal representation of the program.

       • Code synthesis may be done in many sub-phases depending on the quality of code desired.

   • These "phases" of a compiler can be implemented in many ways.

     • In many compiler they are tightly integrated. The parser "method/procedure" invokes the scanner to get a token and then invokes the semantic analyzer or code generator to process each "phrase".

     • In our discussion, we will treat the phases of a compiler as separate processes sending data to one another.

     • It is probably best not to think of them as processing concurrently. Instead think of each phase as taking a complete representation of a program in one form and producing a new, complete representation in some other form.

The Function and Structure of a Compiler