Modern compiler design [PDF]

Chapter 8
Generating Abstract Assembly in C
Chapter Overview
8.1 Creating Abstract Assembly Trees in C
8.1.1 Assembly Language Labels
8.1.2 Interface for Building Abstract Assembly Trees in C
8.1.3 Adding Code to the Semantic Analyzer to Build Abstract Assembly Trees
8.1.4 Functions That Return Abstract Assembly Trees
8.1.5 Variables
8.1.6 Function Prototypes and Function Definitions
8.2 Building Assembly Trees for simpleJava in C
8.2.1 Project Definition
8.2.2 Project Difficulty
8.2.3 Project “Gotcha’s”
8.2.4 Provided Files
8.1 Creating Abstract Assembly Trees in C
To build abstract assembly trees in C, we will first implement an interface that builds assembly trees for
simpleJava statements and expressions, using abstract assembly subtrees. We will then add calls to the
functions defined in this interface to the semantic analyzer, so that the semantic analyzer will build abstract
assembly trees as well as check for semantic errors.
8.1.1 Assembly Language Labels
We will need to generate assembly language labels when building abstract assembly – both for function calls
and for implementing if statements and loops. The file label.h in Figure 8.1 contains prototypes for functions
which allow us to generate both unique labels (such as ifEnd001, ifEnd002, etc), and specific labels (for calls
to library functions, when we know the exact name of the label). The first call to newLabel("foo") returns
the label foo001, the second call returns the label foo002, and so on.
8.1.2 Interface for Building Abstract Assembly Trees in C
The interface for building abstract assembly trees is in Figure 8.2. We will now see some examples of using
these functions to build abstract assembly trees for various statements.
Consider the following simpleJava program:
void foo(int a) {
int b;
int c;
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