understood as processors that match AST patterns of the source language and translate them into patterns in the target language.

Transcription

1 A Basic Compier At a fundamenta eve compiers can be understood as processors that match AST patterns of the source anguage and transate them into patterns in the target anguage. Here we wi ook at a basic compier that transates Cuppa1 programs into exp1bytecode. Chap 6

2 A Basic Compier Cuppa1 Exp1bytecode

3 A Basic Compier Consider for exampe the AST pattern for the assignment statement in Cuppa1, ('assign', name, exp) We coud easiy envision transating this AST pattern into a pattern in Exp1bytecode as foows, store <name> <exp>; where <name> and <exp> are the appropriate transations of the variabe name and the assignment expression from Cuppa1 into Exp1bytecode.

4 A Basic Compier In our case it is not that difficut to come up with pattern transations for a the nonstructured statements and expressions in Cuppa1. For a the non-structured statements we have the pattern transations, ('assign', name, exp) => store <name> <exp>; ('put', exp) => print <exp>; ('get', name) => input <name>;

5 A Basic Compier And for the expressions we have, ('+', c1, c2) => ('+' <c1> <c2>) ('-', c1, c2) => ('-' <c1> <c2>) ('*', c1, c2) => ('*' <c1> <c2>) ('/', c1, c2) => ('/' <c1> <c2>) ('==', c1, c2) => ('==' <c1> <c2>) ('<=', c1, c2) => ('<=' <c1> <c2>) ('id', name) => <name> ('integer', vaue) => <vaue> ('uminus', vaue) => - <vaue> ('not', vaue) =>! <vaue>

6 A Basic Compier One way to transate the AST pattern for the whie oop into a code pattern in Exp1bytecode is, Note that we have to simuate the behavior of the Cuppa1 whie oop with jump statements in Exp1bytecode.

7 A Basic Compier We can do something simiar with if-then statements, Finay, adding the ese-statement to the if-then statement we have,

8 A Basic Compier One thing to keep in mind is the notion of target pattern compositionaity. By that we mean that any target anguage patterns generated from the same cass of AST patterns shoud be abe to be composed, Any one of the Exp1bytecode patterns due to statements in Cuppa1 shoud be abe to be composed with any other Exp1bytecode pattern due to a statement without ever generating incorrect target code. The same thing is true for Exp1bycode patterns generated from Cuppa1 expressions See the noop instructions at the end of the target patterns for whie, if-then, and if-then-ese.

9 A Basic Compier Architecture Our basic compier consists of: The Cuppa1 frontend A code generation tree waker

10 Frontend Pattern Transation Reca that the Cuppa1 frontend generates an AST for a source program, We can easiy appy our pattern transations to generate Exp1bytecode:

11 Codegen Tree Waker The code generator for our compier is a tree waker that waks the Cuppa1 AST and for each AST pattern that appears in a pattern transation rue it wi generate the corresponding target code. Cuppa1 statement patterns wi generate Exp1bytecode instructions on a ist and Cuppa1 expression patterns wi generated Exp1bytecode expressions returned as strings. The reason for this wi become cear ater when we ook at optimizations in this compier.

12 Codegen cuppa1_cc_codegen.py Reca the pattern transation, ('get', name) => input <name>; The codegen tree waker has a function for that, Even though the transation rue for the get statement demands that we aso generate the semicoon as part of the transation, we deay this unti we generate the actua machine instructions. We use Python s abiity to do pattern matching on tupes!

13 Codegen cuppa1_cc_codegen.py Reca the pattern transation, ('assign', name, exp) => store <name> <exp>; The codegen tree waker has a function for that,

14 Codegen Reca the pattern transation, cuppa1_cc_codegen.py The codegen tree waker has a function for that,

15 Codegen cuppa1_cc_codegen.py Reca the pattern transation for binops, The codegen tree waker has a function for that,

16 Codegen cuppa1_cc_codegen.py What remains to be ooked at is how the tree waker deas with Seq nodes since they act as the gue between the statements in the AST we saw above. Reated to this is how the waker deas with Ni nodes in a statement sequence since Seq sequences are Ni terminated.

17 Codegen cuppa1_cc_codegen.py

18 Running Codegen Consider our AST: Generated instruction ist:

19 Formatting the Output Convert the instruction tupe ist into a printabe target program.

20 Running the Phases of the Compier

21 Running the Phases of the Compier

22 Compiation vs Interpretation Compiation Interpretation

23 Compier Correctness We now have two ways to execute a Cuppa1 program: We can interpret the program directy with the Cuppa1 interpreter. We can first transate the Cuppa1 program into Exp1bytecode and then execute the bytecode in the abstract bytecode machine. A compier is correct if the transated program, when executed, gives the same resuts as the interpreted program.

24 Compier Correctness

25 Assignment Assignment #6 see webpage.