Subset-C-Compiler
This is a compiler for a learning purpose.
It can compile subset of c language code to Java bytecode. There is BNF of the language in this repository (see SubsetC.g4 file).
This language has only the following features.
- declare global/local variables
- use int type only
- do four arithmetic operations
- declare functions
- call function
- use if or while statement and comparison operators
Sample
Here is sample code. Save this in Test.jyu file.
int i;
void main() {
i = 2;
int x;
x = 3;
if (i < x) {
mul(i, x);
}
}
int mul(int a, int b) {
return a * b;
}
This sample code can be compiled with this command.
com.sakatakoichi.subsetc.compiler.Compiler Test.jyu
The compiler generates Test.class file.
- global variable is translated into Java static variable.
- function is translated into Java static method.
You can see Java bytecode with javap command.
$ javap -v Test
Classfile /Test.class
Last modified 2018/04/16; size 214 bytes
MD5 checksum 6a83da14906e8a09f82fdba3c412777f
class Test
minor version: 0
major version: 52
flags: (0x0020) ACC_SUPER
this_class: #2 // Test
super_class: #4 // java/lang/Object
interfaces: 0, fields: 1, methods: 2, attributes: 0
Constant pool:
#1 = Utf8 Test
#2 = Class #1 // Test
#3 = Utf8 java/lang/Object
#4 = Class #3 // java/lang/Object
#5 = Utf8 i
#6 = Utf8 I
#7 = NameAndType #5:#6 // i:I
#8 = Fieldref #2.#7 // Test.i:I
#9 = Utf8 ()V
#10 = Utf8 main
#11 = NameAndType #10:#9 // main:()V
#12 = Methodref #2.#11 // Test.main:()V
#13 = Utf8 Code
#14 = Utf8 (II)I
#15 = Utf8 mul
#16 = NameAndType #15:#14 // mul:(II)I
#17 = Methodref #2.#16 // Test.mul:(II)I
{
public static void main();
descriptor: ()V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=0
0: getstatic #8 // Field i:I
3: if_icmpge 20
6: nop
7: iload_0
8: getstatic #8 // Field i:I
11: invokestatic #17 // Method mul:(II)I
14: pop
15: iconst_3
16: istore_0
17: iconst_2
18: putstatic #8 // Field i:I
21: return
public static int mul(int, int);
descriptor: (II)I
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=2, args_size=2
0: iload_0
1: iload_1
2: imul
3: ireturn
}
Here is disassemble Java code from the class file.
class Test
{
private static int i;
public static void main()
{
int j;
if (i < j)
{
mul(j, i);
j = 3;
i = 2;
}
}
public static int mul(int paramInt1, int paramInt2)
{
return paramInt1 * paramInt2;
}
}Resource
I referred to sample code in the book "Compiler and Virtual Machine" (not copied code).