jameslinus / compiler

C → AST → intermediate code → x86 assembly (AT&T)

C compiler using Flex and Bison

##Build make

##Run With a file that needs preprocessing (has #includes, #defines, etc):

gcc -E inputfile.c | ./compile >outputfile.s

Otherwise, from some file:

./compile <inputfile.c >outputfile.s

Or just run ./compile >outputfile.s and type in your code manually.

The outputfile.s file contains x86 assembly (AT&T syntax). To create an executable and run it:

gcc -m32 outputfile.s -o a.out
./a.out

###Options

• -a: show AST
• -d: show declarations
• -q: show quads
• -t: show target code (x86)
• -T: same as -t but also show the quads as comments in target code

Note: if none of the above options are specified, -t will be set by default.

For sample input/output files, see the tests directory.

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##Features

• show AST, declarations, quads, and target code (x86)
• reading and writing local and global variables (including block scopes)
  • ints and int pointers/arrays only
• computation of expressions (most of them)
• call functions with arguments
  • including external ones such as printf, assuming linked
• string literals (necessary to get printf working)
• pointers and pointer indirection
  • array access
  • pointer arithmetic
• most control flow statements (see anti-features section below)

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##Anti-features What this compiler doesn't support:

• certain declarations
  • type specifiers that aren't int or pointers to / arrays of ints
  • type qualifiers (const, volatile, restrict)
  • initialized declarations
  • storage classes
  • anything to do with structs or unions
  • enums
  • typedefs?
  • functions that take parameters
  • multi-dimensional arrays
• certain expressions
  • sizeof
  • casts
  • ternary operator (i.e. a ? b : c)
  • short circuit operators && and ||
    • the operators exist and return 0 or 1; they just don't short circuit
  • division of pointers
  • unary + operator
    • what does this even do
• certain control flow statements
  • do loops
  • switches
  • goto statements
  • labels
• handling of multiple input files hasn't been tested

Things that it does now that could be improved:

• no register allocation
  • currently just uses a separate local variable for each temporary var
• memory leaks everywhere
  • hasn't been a problem yet
  • just don't use this to compile any large and useful programs
• short circuit operators don't actually short circuit
• terribly disorganized
  • do the AST nodes properly!
• quads are internal (the printed quads aren't actually used as input)
• sizes are hardcoded to 4, since only ints/pointers are supported