Repository: benhoyt/pyast64
Branch: master
Commit: e91c97a060de
Files: 10
Total size: 21.5 KB

Directory structure:
gitextract_v98itfbt/

├── .gitignore
├── LICENSE.txt
├── README.md
├── arrays.p64
├── benchmark_for.c
├── benchmark_for.p64
├── compile_and_run.sh
├── forloop.p64
├── print_num.p64
└── pyast64.py

================================================
FILE CONTENTS
================================================

================================================
FILE: .gitignore
================================================
*.exe
*.o
*.s


================================================
FILE: LICENSE.txt
================================================
MIT License

Copyright (c) 2017 Ben Hoyt

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

================================================
FILE: README.md
================================================

pyast64
=======

pyast64 is a Python 3 program that compiles a subset of the Python AST to x64-64 assembler. It's extremely restricted (read "a toy") but it's a nice proof of concept in any case. [Read more about pyast64 here.](http://benhoyt.com/writings/pyast64/)


================================================
FILE: arrays.p64
================================================
# Test arrays

def fetch(array, ofs):
    return array[ofs]

def store(array, ofs, value):
    array[ofs] = value

def print_num(n):
    if n == 0:
        putc(48)  # '0'
        return
    if n < 0:
        putc(45)  # '-' sign
        n = -n
    div = n // 10
    if div != 0:
        print_num(div)
    putc(48 + n % 10)

def main():
    size = 100
    a = array(size)
    for i in range(size):
        store(a, i, i)
    sum = 0
    for i in range(size):
        sum = sum + fetch(a, i)
    print_num(sum)


================================================
FILE: benchmark_for.c
================================================
#include <stdio.h>

int main() {
    long long sum = 0;
    for (long long i = 0; i < 100000000; i++) {
        sum += i;
    }
    return (int)sum;
}


================================================
FILE: benchmark_for.p64
================================================
# Benchmark a for loop

# python3.5: 7.002s
# pyast64: 0.548s (12.7x)
# pyast64_peephole: 0.236s (29.7x, 2.3x)

def main():
    sum = 0
    for i in range(100000000):
        sum += i


================================================
FILE: compile_and_run.sh
================================================
#!/usr/bin/env bash

set -e

fullname="$1"
fname=${fullname%.*}

python pyast64.py $1 > $fname.s
as $fname.s -o $fname.o
ld $fname.o -e _main -o $fname.exe -w
./$fname.exe
echo


================================================
FILE: forloop.p64
================================================
# Basic for loop

def loop():
    for i in range(10):
        putc(65 + i)

def main():
    loop()


================================================
FILE: print_num.p64
================================================
# Convert a number to decimal and print it

def print_num(n):
    if n == 0:
        putc(48)  # '0'
        return
    if n < 0:
        putc(45)  # '-' sign
        n = -n
    div = n // 10
    if div != 0:
        print_num(div)
    putc(48 + n % 10)

def newline():
    putc(10)

def main():
    print_num(1234)
    newline()
    print_num(-404)
    newline()
    print_num(0)


================================================
FILE: pyast64.py
================================================
"""Compile a subset of the Python AST to x64-64 assembler.

Read more about it here: http://benhoyt.com/writings/pyast64/

Released under a permissive MIT license (see LICENSE.txt).
"""

import argparse
import ast
import sys


class Assembler:
    """The Assembler takes care of outputting instructions, labels, etc.,
    as well as a simple peephole optimization to combine sequences of pushes
    and pops.
    """

    def __init__(self, output_file=sys.stdout, peephole=True):
        self.output_file = output_file
        self.peephole = peephole
        # Current batch of instructions, flushed on label and end of function
        self.batch = []

    def flush(self):
        if self.peephole:
            self.optimize_pushes_pops()
        for opcode, args in self.batch:
            print('\t{}\t{}'.format(opcode, ', '.join(str(a) for a in args)),
                  file=self.output_file)
        self.batch = []

    def optimize_pushes_pops(self):
        """This finds runs of push(es) followed by pop(s) and combines
        them into simpler, faster mov instructions. For example:

        pushq   8(%rbp)
        pushq   $100
        popq    %rdx
        popq    %rax

        Will be turned into:

        movq    $100, %rdx
        movq    8(%rbp), %rax
        """
        state = 'default'
        optimized = []
        pushes = 0
        pops = 0

        # This nested function combines a sequence of pushes and pops
        def combine():
            mid = len(optimized) - pops
            num = min(pushes, pops)
            moves = []
            for i in range(num):
                pop_arg = optimized[mid + i][1][0]
                push_arg = optimized[mid - i - 1][1][0]
                if push_arg != pop_arg:
                    moves.append(('movq', [push_arg, pop_arg]))
            optimized[mid - num:mid + num] = moves

        # This loop actually finds the sequences
        for opcode, args in self.batch:
            if state == 'default':
                if opcode == 'pushq':
                    state = 'push'
                    pushes += 1
                else:
                    pushes = 0
                    pops = 0
                optimized.append((opcode, args))
            elif state == 'push':
                if opcode == 'pushq':
                    pushes += 1
                elif opcode == 'popq':
                    state = 'pop'
                    pops += 1
                else:
                    state = 'default'
                    pushes = 0
                    pops = 0
                optimized.append((opcode, args))
            elif state == 'pop':
                if opcode == 'popq':
                    pops += 1
                elif opcode == 'pushq':
                    combine()
                    state = 'push'
                    pushes = 1
                    pops = 0
                else:
                    combine()
                    state = 'default'
                    pushes = 0
                    pops = 0
                optimized.append((opcode, args))
            else:
                assert False, 'bad state: {}'.format(state)
        if state == 'pop':
            combine()
        self.batch = optimized

    def instr(self, opcode, *args):
        self.batch.append((opcode, args))

    def label(self, name):
        self.flush()
        print('{}:'.format(name), file=self.output_file)

    def directive(self, line):
        self.flush()
        print(line, file=self.output_file)

    def comment(self, text):
        self.flush()
        print('# {}'.format(text), file=self.output_file)


class LocalsVisitor(ast.NodeVisitor):
    """Recursively visit a FunctionDef node to find all the locals
    (so we can allocate the right amount of stack space for them).
    """

    def __init__(self):
        self.local_names = []
        self.global_names = []
        self.function_calls = []

    def add(self, name):
        if name not in self.local_names and name not in self.global_names:
            self.local_names.append(name)

    def visit_Global(self, node):
        self.global_names.extend(node.names)

    def visit_Assign(self, node):
        assert len(node.targets) == 1, \
            'can only assign one variable at a time'
        self.visit(node.value)
        target = node.targets[0]
        if isinstance(target, ast.Subscript):
            self.add(target.value.id)
        else:
            self.add(target.id)

    def visit_For(self, node):
        self.add(node.target.id)
        for statement in node.body:
            self.visit(statement)

    def visit_Call(self, node):
        self.function_calls.append(node.func.id)


class Compiler:
    """The main Python AST -> x86-64 compiler."""

    def __init__(self, assembler=None, peephole=True):
        if assembler is None:
            assembler = Assembler(peephole=peephole)
        self.asm = assembler
        self.func = None

    def compile(self, node):
        self.header()
        self.visit(node)
        self.footer()

    def visit(self, node):
        # We could have subclassed ast.NodeVisitor, but it's better to fail
        # hard on AST nodes we don't support
        name = node.__class__.__name__
        visit_func = getattr(self, 'visit_' + name, None)
        assert visit_func is not None, '{} not supported - node {}'.format(
                name, ast.dump(node))
        visit_func(node)

    def header(self):
        self.asm.directive('.section __TEXT, __text')
        self.asm.comment('')

    def footer(self):
        self.compile_putc()
        self.asm.flush()

    def compile_putc(self):
        # Insert this into every program so it can call putc() for output
        self.asm.label('putc')
        self.compile_enter()
        self.asm.instr('movl', '$0x2000004', '%eax')    # write
        self.asm.instr('movl', '$1', '%edi')            # stdout
        self.asm.instr('movq', '%rbp', '%rsi')          # address
        self.asm.instr('addq', '$16', '%rsi')
        self.asm.instr('movq', '$1', '%rdx')            # length
        self.asm.instr('syscall')
        self.compile_return(has_arrays=False)

    def visit_Module(self, node):
        for statement in node.body:
            self.visit(statement)

    def visit_FunctionDef(self, node):
        assert self.func is None, 'nested functions not supported'
        assert node.args.vararg is None, '*args not supported'
        assert not node.args.kwonlyargs, 'keyword-only args not supported'
        assert not node.args.kwarg, 'keyword args not supported'

        self.func = node.name
        self.label_num = 1
        self.locals = {a.arg: i for i, a in enumerate(node.args.args)}

        # Find names of additional locals assigned in this function
        locals_visitor = LocalsVisitor()
        locals_visitor.visit(node)
        for name in locals_visitor.local_names:
            if name not in self.locals:
                self.locals[name] = len(self.locals) + 1
        if 'array' in locals_visitor.function_calls:
            self.locals['_array_size'] = len(self.locals) + 1
        self.globals = set(locals_visitor.global_names)
        self.break_labels = []

        # Function label and header
        if node.name == 'main':
            self.asm.directive('.globl _main')
            self.asm.label('_main')
        else:
            self.asm.label(node.name)
        self.num_extra_locals = len(self.locals) - len(node.args.args)
        self.compile_enter(self.num_extra_locals)

        # Now compile all the statements in the function body
        for statement in node.body:
            self.visit(statement)

        if not isinstance(node.body[-1], ast.Return):
            # Function didn't have explicit return at the end,
            # compile return now (or exit for "main")
            if self.func == 'main':
                self.compile_exit(0)
            else:
                self.compile_return(self.num_extra_locals)

        self.asm.comment('')
        self.func = None

    def compile_enter(self, num_extra_locals=0):
        # Make space for extra locals (in addition to the arguments)
        for i in range(num_extra_locals):
            self.asm.instr('pushq', '$0')
        # Use rbp for a stack frame pointer
        self.asm.instr('pushq', '%rbp')
        self.asm.instr('movq', '%rsp', '%rbp')

    def compile_return(self, num_extra_locals=0, has_arrays=None):
        if has_arrays is None:
            has_arrays = '_array_size' in self.locals
        if has_arrays:
            offset = self.local_offset('_array_size')
            self.asm.instr('movq', '{}(%rbp)'.format(offset), '%rbx')
            self.asm.instr('addq', '%rbx', '%rsp')
        self.asm.instr('popq', '%rbp')
        if num_extra_locals > 0:
            self.asm.instr('leaq', '{}(%rsp),%rsp'.format(
                    num_extra_locals * 8))
        self.asm.instr('ret')

    def compile_exit(self, return_code):
        if return_code is None:
            self.asm.instr('popq', '%rdi')
        else:
            self.asm.instr('movl', '${}'.format(return_code), '%edi')
        self.asm.instr('movl', '$0x2000001', '%eax')
        self.asm.instr('syscall')

    def visit_Return(self, node):
        if node.value:
            self.visit(node.value)
        if self.func == 'main':
            # Returning from main, exit with that return code
            self.compile_exit(None if node.value else 0)
        else:
            if node.value:
                self.asm.instr('popq', '%rax')
            self.compile_return(self.num_extra_locals)

    def visit_Num(self, node):
        self.asm.instr('pushq', '${}'.format(node.n))

    def local_offset(self, name):
        index = self.locals[name]
        return (len(self.locals) - index) * 8 + 8

    def visit_Name(self, node):
        # Only supports locals, not globals
        offset = self.local_offset(node.id)
        self.asm.instr('pushq', '{}(%rbp)'.format(offset))

    def visit_Assign(self, node):
        # Only supports assignment of (a single) local variable
        assert len(node.targets) == 1, \
            'can only assign one variable at a time'
        self.visit(node.value)
        target = node.targets[0]
        if isinstance(target, ast.Subscript):
            # array[offset] = value
            self.visit(target.slice.value)
            self.asm.instr('popq', '%rax')
            self.asm.instr('popq', '%rbx')
            local_offset = self.local_offset(target.value.id)
            self.asm.instr('movq', '{}(%rbp)'.format(local_offset), '%rdx')
            self.asm.instr('movq', '%rbx', '(%rdx,%rax,8)')
        else:
            # variable = value
            offset = self.local_offset(node.targets[0].id)
            self.asm.instr('popq', '{}(%rbp)'.format(offset))

    def visit_AugAssign(self, node):
        # Handles "n += 1" and the like
        self.visit(node.target)
        self.visit(node.value)
        self.visit(node.op)
        offset = self.local_offset(node.target.id)
        self.asm.instr('popq', '{}(%rbp)'.format(offset))

    def simple_binop(self, op):
        self.asm.instr('popq', '%rdx')
        self.asm.instr('popq', '%rax')
        self.asm.instr(op, '%rdx', '%rax')
        self.asm.instr('pushq', '%rax')

    def visit_Mult(self, node):
        self.asm.instr('popq', '%rdx')
        self.asm.instr('popq', '%rax')
        self.asm.instr('imulq', '%rdx')
        self.asm.instr('pushq', '%rax')

    def compile_divide(self, push_reg):
        self.asm.instr('popq', '%rbx')
        self.asm.instr('popq', '%rax')
        self.asm.instr('cqo')
        self.asm.instr('idiv', '%rbx')
        self.asm.instr('pushq', push_reg)

    def visit_Mod(self, node):
        self.compile_divide('%rdx')

    def visit_FloorDiv(self, node):
        self.compile_divide('%rax')

    def visit_Add(self, node):
        self.simple_binop('addq')

    def visit_Sub(self, node):
        self.simple_binop('subq')

    def visit_BinOp(self, node):
        self.visit(node.left)
        self.visit(node.right)
        self.visit(node.op)

    def visit_UnaryOp(self, node):
        assert isinstance(node.op, ast.USub), \
            'only unary minus is supported, not {}'.format(node.op.__class__.__name__)
        self.visit(ast.Num(n=0))
        self.visit(node.operand)
        self.visit(ast.Sub())

    def visit_Expr(self, node):
        self.visit(node.value)
        self.asm.instr('popq', '%rax')

    def visit_And(self, node):
        self.simple_binop('and')

    def visit_BitAnd(self, node):
        self.simple_binop('and')

    def visit_Or(self, node):
        self.simple_binop('or')

    def visit_BitOr(self, node):
        self.simple_binop('or')

    def visit_BitXor(self, node):
        self.simple_binop('xor')

    def visit_BoolOp(self, node):
        self.visit(node.values[0])
        for value in node.values[1:]:
            self.visit(value)
            self.visit(node.op)

    def builtin_array(self, args):
        assert len(args) == 1, 'array(len) expected 1 arg, not {}'.format(len(args))
        self.visit(args[0])
        # Allocate array on stack, add size to _array_size, push address
        self.asm.instr('popq', '%rax')
        self.asm.instr('shlq', '$3', '%rax')  # len*8 to get size in bytes
        offset = self.local_offset('_array_size')
        self.asm.instr('addq', '%rax', '{}(%rbp)'.format(offset))
        self.asm.instr('subq', '%rax', '%rsp')
        self.asm.instr('movq', '%rsp', '%rax')
        self.asm.instr('pushq', '%rax')

    def visit_Call(self, node):
        assert not node.keywords, 'keyword args not supported'
        builtin = getattr(self, 'builtin_{}'.format(node.func.id), None)
        if builtin is not None:
            builtin(node.args)
        else:
            for arg in node.args:
                self.visit(arg)
            self.asm.instr('call', node.func.id)
            if node.args:
                # Caller cleans up the arguments from the stack
                self.asm.instr('addq', '${}'.format(8 * len(node.args)), '%rsp')
            # Return value is in rax, so push it on the stack now
            self.asm.instr('pushq', '%rax')

    def label(self, slug):
        label = '{}_{}_{}'.format(self.func, self.label_num, slug)
        self.label_num += 1
        return label

    def visit_Compare(self, node):
        assert len(node.ops) == 1, 'only single comparisons supported'
        self.visit(node.left)
        self.visit(node.comparators[0])
        self.visit(node.ops[0])

    def compile_comparison(self, jump_not, slug):
        self.asm.instr('popq', '%rdx')
        self.asm.instr('popq', '%rax')
        self.asm.instr('cmpq', '%rdx', '%rax')
        self.asm.instr('movq', '$0', '%rax')
        label = self.label(slug)
        self.asm.instr(jump_not, label)
        self.asm.instr('incq', '%rax')
        self.asm.label(label)
        self.asm.instr('pushq', '%rax')

    def visit_Lt(self, node):
        self.compile_comparison('jnl', 'less')

    def visit_LtE(self, node):
        self.compile_comparison('jnle', 'less_or_equal')

    def visit_Gt(self, node):
        self.compile_comparison('jng', 'greater')

    def visit_GtE(self, node):
        self.compile_comparison('jnge', 'greater_or_equal')

    def visit_Eq(self, node):
        self.compile_comparison('jne', 'equal')

    def visit_NotEq(self, node):
        self.compile_comparison('je', 'not_equal')

    def visit_If(self, node):
        # Handles if, elif, and else
        self.visit(node.test)
        self.asm.instr('popq', '%rax')
        self.asm.instr('cmpq', '$0', '%rax')
        label_else = self.label('else')
        label_end = self.label('end')
        self.asm.instr('jz', label_else)
        for statement in node.body:
            self.visit(statement)
        if node.orelse:
            self.asm.instr('jmp', label_end)
        self.asm.label(label_else)
        for statement in node.orelse:
            self.visit(statement)
        if node.orelse:
            self.asm.label(label_end)

    def visit_While(self, node):
        # Handles while and break (also used for "for" -- see below)
        while_label = self.label('while')
        break_label = self.label('break')
        self.break_labels.append(break_label)
        self.asm.label(while_label)
        self.visit(node.test)
        self.asm.instr('popq', '%rax')
        self.asm.instr('cmpq', '$0', '%rax')
        self.asm.instr('jz', break_label)
        for statement in node.body:
            self.visit(statement)
        self.asm.instr('jmp', while_label)
        self.asm.label(break_label)
        self.break_labels.pop()

    def visit_Break(self, node):
        self.asm.instr('jmp', self.break_labels[-1])

    def visit_Pass(self, node):
        pass

    def visit_For(self, node):
        # Turn for+range loop into a while loop:
        #   i = start
        #   while i < stop:
        #       body
        #       i = i + step
        assert isinstance(node.iter, ast.Call) and \
            node.iter.func.id == 'range', \
            'for can only be used with range()'
        range_args = node.iter.args
        if len(range_args) == 1:
            start = ast.Num(n=0)
            stop = range_args[0]
            step = ast.Num(n=1)
        elif len(range_args) == 2:
            start, stop = range_args
            step = ast.Num(n=1)
        else:
            start, stop, step = range_args
            if (isinstance(step, ast.UnaryOp) and
                    isinstance(step.op, ast.USub) and
                    isinstance(step.operand, ast.Num)):
                # Handle negative step
                step = ast.Num(n=-step.operand.n)
            assert isinstance(step, ast.Num) and step.n != 0, \
                'range() step must be a nonzero integer constant'
        self.visit(ast.Assign(targets=[node.target], value=start))
        test = ast.Compare(
            left=node.target,
            ops=[ast.Lt() if step.n > 0 else ast.Gt()],
            comparators=[stop],
        )
        incr = ast.Assign(
            targets=[node.target],
            value=ast.BinOp(left=node.target, op=ast.Add(), right=step),
        )
        self.visit(ast.While(test=test, body=node.body + [incr]))

    def visit_Global(self, node):
        # Global names are already collected by LocalsVisitor
        pass

    def visit_Subscript(self, node):
        self.visit(node.slice.value)
        self.asm.instr('popq', '%rax')
        local_offset = self.local_offset(node.value.id)
        self.asm.instr('movq', '{}(%rbp)'.format(local_offset), '%rdx')
        self.asm.instr('pushq', '(%rdx,%rax,8)')


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('filename', help='filename to compile')
    parser.add_argument('-n', '--no-peephole', action='store_true',
                        help='enable peephole assembler optimizer')
    args = parser.parse_args()

    with open(args.filename) as f:
        source = f.read()
    node = ast.parse(source, filename=args.filename)
    compiler = Compiler(peephole=not args.no_peephole)
    compiler.compile(node)