"""
Classes for a RiscV CFG: :py:class:`CFG` for the CFG itself,
and :py:class:`Block` for its basic blocks.
"""
from graphviz import Digraph # for dot output
from typing import cast, Any, Dict, List, Set, Iterator
from Lib.Errors import MiniCInternalError
from Lib.Operands import (Operand, Immediate, Function, A0)
from Lib.Statement import (
Statement, Instru3A, Label,
AbsoluteJump, ConditionalJump, Comment
)
from Lib.Terminator import (
Terminator, BranchingTerminator, Return)
from Lib.FunctionData import (FunctionData, _iter_statements, _print_code)
BlockInstr = Instru3A | Comment
class Block:
"""
A basic block of a :py:class:`CFG` is made of three main parts:
- a start :py:class:`label <Lib.Statement.Label>` that uniquely identifies the block in the CFG
- the main body of the block, a list of instructions
(excluding labels, jumps and branching instructions)
- a :py:class:`terminator <Lib.Terminator.Terminator>`
that represents the final jump or branching instruction of the block,
and points to the successors of the block.
See the documentation for :py:class:`Lib.Terminator.Terminator` for further explanations.
"""
_terminator: Terminator
_label: Label
_phis: List[Statement]
_instructions: List[BlockInstr]
_in: List['Block']
_gen: Set
_kill: Set
def __init__(self, label: Label, insts: List[BlockInstr], terminator: Terminator):
self._label = label
self._instructions = insts
self._in = []
self._phis = []
self._terminator = terminator
self._gen = set()
self._kill = set()
def __str__(self):
instr = [i for i in self._instructions if not isinstance(i, Comment)]
instr_str = '\n'.join(map(str, instr))
s = '{}:\n\n{}'.format(self._label, instr_str)
return s
def to_dot(self) -> str: # pragma: no cover
"""Outputs all statements of the block as a string."""
# dot is weird: lines ending with \l instead of \n are left-aligned.
NEWLINE = '\\l '
instr = []
instr += self._phis
instr += [i for i in self._instructions if not isinstance(i, Comment)]
instr += [self.get_terminator()]
instr_str = NEWLINE.join(map(str, instr))
s = '{}:{}{}\\l'.format(self._label, NEWLINE, instr_str)
return s
def __repr__(self):
return str(self._label)
def get_body(self) -> List[BlockInstr]:
"""Return the statements in the body of the block (no phi-node nor the terminator)."""
return self._instructions
def get_all_statements(self) -> List[Statement]:
"""
Return all statements of the block
(including phi-nodes and the terminator, but not the label of the block).
"""
return (self._phis +
cast(List[Statement], self._instructions) +
[self.get_terminator()])
def get_body_and_terminator(self) -> List[Statement]:
"""
Return all statements of the block, except phi-nodes
(and the label of the block).
"""
return (cast(List[Statement], self._instructions) +
[self.get_terminator()])
def get_label(self) -> Label:
"""Return the label of the block."""
return self._label
def get_in(self) -> List['Block']:
"""Return the list of blocks with an edge to the considered block."""
return self._in
def get_terminator(self) -> Terminator:
"""Return the terminator of the block."""
return self._terminator
def set_terminator(self, term: Terminator) -> None:
"""Set the terminator of the block."""
self._terminator = term
def get_phis(self) -> List[Statement]:
"""Return the list of all φ instructions of the block."""
return self._phis
def add_phi(self, phi: Statement) -> None:
"""Add a φ instruction to the block."""
self._phis.append(phi)
def set_phis(self, phis: List[Statement]) -> None:
"""Replace the φ instructions in the block by the given list `phis`."""
self._phis = phis
def remove_all_phis(self) -> None:
"""Remove all φ instructions in the block."""
self._phis = []
def iter_statements(self, f) -> None:
"""Iterate over instructions.
For each real instruction i (not label or comment), replace it
with the list of instructions given by f(i).
Assume there is no phi-node.
"""
assert (self._phis == [])
new_statements = _iter_statements(self._instructions, f)
end_statements = f(self.get_terminator())
if len(end_statements) >= 1 and isinstance(end_statements[-1], Terminator):
new_terminator = end_statements.pop(-1)
self._instructions = new_statements + end_statements
self.set_terminator(new_terminator)
else:
raise MiniCInternalError(
"Block.iter_statements: Invalid replacement for terminator {}:\n {}"
.format(self.get_terminator(), end_statements))
def add_instruction(self, instr: BlockInstr) -> None:
"""Add an instruction to the body of the block."""
self._instructions.append(instr)
class CFG:
"""
A complete control-flow graph representing a function.
This class is mainly made of a list of basic :py:class:`Block`,
a label indicating the :py:meth:`entry point of the function <get_start>`,
and an :py:meth:`exit label <get_end>`.
As with linear code, metadata about the function can be found
in the :py:attr:`fdata` member variable.
"""
_start: Label
_end: Label
_blocks: Dict[Label, Block]
#: Metadata about the function represented by this CFG
fdata: FunctionData
def __init__(self, fdata: FunctionData):
self._blocks = {}
self.fdata = fdata
self._init_blks()
self._end = self.fdata.fresh_label("end")
def _init_blks(self) -> None:
"""Add a block for division by 0."""
# Label for the address of the error message
# This address is added by print_code
label_div_by_zero_msg = Label(self.fdata._label_div_by_zero.name + "_msg")
blk = Block(self.fdata._label_div_by_zero, [
Instru3A("la", A0, label_div_by_zero_msg),
Instru3A("call", Function("println_string")),
Instru3A("li", A0, Immediate(1)),
Instru3A("call", Function("exit")),
], terminator=Return())
self.add_block(blk)
def get_start(self) -> Label:
"""Return the entry label of the CFG."""
return self._start
def set_start(self, start: Label) -> None:
"""Set the entry label of the CFG."""
assert (start in self._blocks)
self._start = start
def get_end(self) -> Label:
"""Return the exit label of the CFG."""
return self._end
def add_block(self, blk: Block) -> None:
"""Add a new block to the CFG."""
self._blocks[blk._label] = blk
def get_block(self, name: Label) -> Block:
"""Return the block with label `name`."""
return self._blocks[name]
def get_blocks(self) -> List[Block]:
"""Return all the blocks."""
return [b for b in self._blocks.values()]
def get_entries(self) -> List[Block]:
"""Return all the blocks with no predecessors."""
return [b for b in self._blocks.values() if not b.get_in()]
def add_edge(self, src: Block, dest: Block) -> None:
"""Add the edge src -> dest in the control flow graph."""
dest.get_in().append(src)
# assert (dest.get_label() in src.get_terminator().targets())
def remove_edge(self, src: Block, dest: Block) -> None:
"""Remove the edge src -> dest in the control flow graph."""
dest.get_in().remove(src)
# assert (dest.get_label() not in src.get_terminator().targets())
def out_blocks(self, block: Block) -> List[Block]:
"""
Return the list of blocks in the CFG targeted by
the Terminator of Block block.
"""
return [self.get_block(dest) for dest in block.get_terminator().targets()]
def gather_defs(self) -> Dict[Any, Set[Block]]:
"""
Return a dictionary associating variables to all the blocks
containing one of their definitions.
"""
defs: Dict[Operand, Set[Block]] = dict()
for b in self.get_blocks():
for i in b.get_all_statements():
for v in i.defined():
if v not in defs:
defs[v] = {b}
else:
defs[v].add(b)
return defs
def iter_statements(self, f) -> None:
"""Apply f to all instructions in all the blocks."""
for b in self.get_blocks():
b.iter_statements(f)
def linearize_naive(self) -> Iterator[Statement]:
"""
Linearize the given control flow graph as a list of instructions.
Naive procedure that adds jumps everywhere.
"""
for label, block in self._blocks.items():
yield label
for i in block._instructions:
yield i
match block.get_terminator():
case BranchingTerminator() as j:
# In case of conditional jump, add the missing edge
yield ConditionalJump(j.cond, j.op1, j.op2, j.label_then)
yield AbsoluteJump(j.label_else)
case AbsoluteJump() as j:
yield AbsoluteJump(j.label)
case Return():
yield AbsoluteJump(self.get_end())
def print_code(self, output, linearize=(lambda cfg: list(cfg.linearize_naive())),
comment=None) -> None:
"""Print the linearization of the CFG."""
statements = linearize(self)
_print_code(statements, self.fdata, output, init_label=self._start,
fin_label=self._end, fin_div0=False, comment=comment)
def print_dot(self, filename, DF=None, view=False) -> None: # pragma: no cover
"""Print the CFG as a graph."""
graph = Digraph()
# nodes
for name, blk in self._blocks.items():
if DF is not None:
df_str = "{}" if blk not in DF or not len(DF[blk]) else str(DF[blk])
df_lab = blk.to_dot() + "\n\nDominance frontier:\n" + df_str
else:
df_lab = blk.to_dot()
graph.node(str(blk._label), label=df_lab, shape='rectangle')
# edges
for name, blk in self._blocks.items():
for child in blk.get_terminator().targets():
graph.edge(str(blk._label), str(child))
graph.render(filename, view=view)