""" Programming Language for 6502/6510 microprocessors, codename 'Sick' This is the optimizer that applies various optimizations to the parse tree. Written by Irmen de Jong (irmen@razorvine.net) - license: GNU GPL 3.0 """ from .plyparse import Module, Subroutine, Block, Directive, Assignment, AugAssignment, Goto, Expression from .plylex import print_warning, print_bold class Optimizer: def __init__(self, mod: Module) -> None: self.num_warnings = 0 self.module = mod def optimize(self) -> None: self.num_warnings = 0 self.remove_useless_assigns() self.combine_assignments_into_multi() self.optimize_multiassigns() self.remove_unused_subroutines() self.optimize_compare_with_zero() self.remove_empty_blocks() def remove_useless_assigns(self): # remove assignment statements that do nothing (A=A) # and augmented assignments that have no effect (A+=0) # @todo remove or simplify logical aug assigns like A |= 0, A |= true, A |= false (or perhaps turn them into byte values first?) for block, parent in self.module.all_scopes(): for assignment in list(block.nodes): if isinstance(assignment, Assignment): assignment.left = [lv for lv in assignment.left if lv != assignment.right] if not assignment.left: block.scope.remove_node(assignment) self.num_warnings += 1 print_warning("{}: removed statement that has no effect".format(assignment.sourceref)) if isinstance(assignment, AugAssignment): if isinstance(assignment.right, (int, float)): if assignment.right == 0 and assignment.operator in ("+=", "-=", "|=", "<<=", ">>=", "^="): self.num_warnings += 1 print_warning("{}: removed statement that has no effect".format(assignment.sourceref)) block.scope.remove_node(assignment) if assignment.right >= 8 and assignment.operator in ("<<=", ">>="): print("{}: shifting result is always zero".format(assignment.sourceref)) new_stmt = Assignment(left=[assignment.left], right=0, sourceref=assignment.sourceref) block.scope.replace_node(assignment, new_stmt) def combine_assignments_into_multi(self): # fold multiple consecutive assignments with the same rvalue into one multi-assignment for block, parent in self.module.all_scopes(): rvalue = None assignments = [] for stmt in list(block.nodes): if isinstance(stmt, Assignment): if assignments: if stmt.right == rvalue: assignments.append(stmt) continue elif len(assignments) > 1: # replace the first assignment by a multi-assign with all the others for assignment in assignments[1:]: print("{}: joined with previous assignment".format(assignment.sourceref)) assignments[0].left.extend(assignment.left) block.scope.remove_node(assignment) rvalue = None assignments.clear() else: rvalue = stmt.right assignments.append(stmt) else: rvalue = None assignments.clear() def optimize_multiassigns(self): # optimize multi-assign statements (remove duplicate targets, optimize order) for block, parent in self.module.all_scopes(): for assignment in block.nodes: if isinstance(assignment, Assignment) and len(assignment.left) > 1: # remove duplicates lvalues = set(assignment.left) if len(lvalues) != len(assignment.left): print("{}: removed duplicate assignment targets".format(assignment.sourceref)) # @todo change order: first registers, then zp addresses, then non-zp addresses, then the rest (if any) assignment.left = list(lvalues) def remove_unused_subroutines(self): # some symbols are used by the emitted assembly code from the code generator, # and should never be removed or the assembler will fail never_remove = {"c64.FREADUY", "c64.FTOMEMXY", "c64.FADD", "c64.FSUB", "c64flt.GIVUAYF", "c64flt.copy_mflt", "c64flt.float_add_one", "c64flt.float_sub_one", "c64flt.float_add_SW1_to_XY", "c64flt.float_sub_SW1_from_XY"} num_discarded = 0 for sub, parent in self.module.all_scopes(): if isinstance(sub, Subroutine): usages = self.module.subroutine_usage[(parent.name, sub.name)] if not usages and parent.name + '.' + sub.name not in never_remove: parent.scope.remove_node(sub) num_discarded += 1 if num_discarded: print("discarded {:d} unused subroutines".format(num_discarded)) def optimize_compare_with_zero(self): # a conditional goto that compares a value with zero will be simplified # the comparison operator and rvalue (0) will be removed and the if-status changed accordingly for block, parent in self.module.all_scopes(): if block.scope: for stmt in block.scope.filter_nodes(Goto): if isinstance(stmt.condition, Expression): print("NOT IMPLEMENTED YET: optimize goto conditionals", stmt.condition) # @todo # if cond and isinstance(cond.rvalue, (int, float)) and cond.rvalue.value == 0: # simplified = False # if cond.ifstatus in ("true", "ne"): # if cond.comparison_op == "==": # # if_true something == 0 -> if_not something # cond.ifstatus = "not" # cond.comparison_op, cond.rvalue = "", None # simplified = True # elif cond.comparison_op == "!=": # # if_true something != 0 -> if_true something # cond.comparison_op, cond.rvalue = "", None # simplified = True # elif cond.ifstatus in ("not", "eq"): # if cond.comparison_op == "==": # # if_not something == 0 -> if_true something # cond.ifstatus = "true" # cond.comparison_op, cond.rvalue = "", None # simplified = True # elif cond.comparison_op == "!=": # # if_not something != 0 -> if_not something # cond.comparison_op, cond.rvalue = "", None # simplified = True # if simplified: # print("{}: simplified comparison with zero".format(stmt.sourceref)) def remove_empty_blocks(self) -> None: # remove blocks without name and without address, or that are empty for node, parent in self.module.all_scopes(): if isinstance(node, (Subroutine, Block)): if not node.scope: continue if all(isinstance(n, Directive) for n in node.scope.nodes): empty = True for n in node.scope.nodes: empty = empty and n.name not in {"asmbinary", "asminclude"} if empty: self.num_warnings += 1 print_warning("ignoring empty block or subroutine", node.sourceref) assert isinstance(parent, (Block, Module)) parent.scope.nodes.remove(node) if isinstance(node, Block): if not node.name and node.address is None: self.num_warnings += 1 print_warning("ignoring block without name and address", node.sourceref) assert isinstance(parent, Module) parent.scope.nodes.remove(node) def optimize(mod: Module) -> None: opt = Optimizer(mod) opt.optimize() if opt.num_warnings: print_bold("There are {:d} optimization warnings.".format(opt.num_warnings))