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Task 2: RISC-V Code generator

Summary

In this task, you are going to implement a code generator targeting RISC-V assembly for the same simple programming language. For this task, we assume that the input program has passed both the syntax and semantic analysis (Task 1). We will once again use the parser generator ANTLR as our main tool to reduce the amount of hand-written code required.

The generated code, which is printed to System.out, should be valid and executable RISC-V assembly code, and in particular contains a label main (where the program starts execution). For your reference, we provide the assembler interface (based on RARS's Java API) that we use to verify your generated code.

Input / output specification

Your code generator will read a string (the input program in our simple programming language) from System.in; the input program is assumed to satisfy all the type deduction rules of Task 1. It will generate RISC-V assembly code that implements the input program — in particular, the generated code can be simulated by RARS through the provided assembler interface, which does the following (with a "bootstrap loader" snippet) before jumping to the label main:

  1. Pushes a return value onto the stack (whose value will be modified by your generated code).
  2. Pushes the arguments (by convention, in reverse order) onto the stack.
  3. Pushes the return address — the address right after the jump — onto the stack.

After the generated code finishes its operations, it should jump back to the return address (3. above), and the only value left on the stack should be the return value of main (1. above). As a concrete example, twoargs.asm is generated from a main function that takes two integer arguments and prints them to the screen. If we have placed rars_27a7c1f.jar and RARSInterface.java in the current folder, we can run twoargs.asm as follows:

  • On -nix based systems:

    We can pipe RISC-V assembly code into RARS with the shell command:

    cat twoargs.asm | java -classpath ./rars_27a7c1f.jar ./RARSInterface.java 3 5

  • On Windows systems:

    We can pipe RISC-V assembly code into RARS on the command line using:

    cmd /c "(type .\twoargs.asm) | java -classpath .\rars_27a7c1f.jar .\RARSInterface.java 3 5"