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CS 444/544 Compilers
Spring 2017

Assignment: Code Generation, Phase 1

In this assignment you will implement the code generation phase of the Cool compiler for non-object-oriented features of the language.

DUE: March 30th, Thursday, 23:55.

Overview

In this phase, we will write code generation capability for the following subset of Cool:

That is, we assume that the input programs will contain a single Main class with a single method named main. There will be no object-related expressions; i.e. dynamic or static dispatch, case, isvoid, or new.

The only types you must support are Int and Bool; in particular, String is not included because it requires objects, and SELF_TYPE is not needed in the absence of objects. Additionally, in this phase, a loop expression has type Int and evaluates to the value 0.

The input to the code generator is the AST. We assume that the AST have passed through semantic analysis for any potential errors; so, do not attempt to do error checking during code generation, it’s unnecessary.

As usual, a starter code will be provided for your convenience, including several test inputs.

Notes

  1. You can just generate Int and Bool constants as the i32 and i1 LLVM primitives.

  2. Some parts of the code generator, such as the arithmetic and comparison operators, have been written for you. Make sure you understand the given code very well.

  3. Test your compiler! Test it often.

  4. Since a let-variable has a local scope, we can allocate it in the current stack frame using the alloca instruction. All alloca instructions should be placed in the entry of the let-block to enable the mem2reg optimization so that let-variable can be promoted from the memory to an SSA register later on.

  5. Manage the environment carefully to introduce or remove bindings according to scoping rules.

  6. For if-then-else, you will need to utilize LLVM’s BasicBlocks. The given code for loops shows you an example. The special thing about if-then-else is that the result of an if-then-else is a merge of the results of the two branches. For this part, we assume that the both branches evaluate to Ints. So, you can allocate an i32 in the stack right before or after generating code for the condition, and then store a different result into this allocated slot in each of the branches. Finally, at the merge block, load the value stored into this slot to get the result of if-then-else.