mirror of https://github.com/m-labs/artiq
84 lines
2.9 KiB
Python
84 lines
2.9 KiB
Python
"""
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:class:`DeadCodeEliminator` is a dead code elimination transform:
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it only basic blocks with no predecessors as well as unused
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instructions without side effects.
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"""
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from .. import ir
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class DeadCodeEliminator:
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def __init__(self, engine):
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self.engine = engine
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def process(self, functions):
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for func in functions:
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self.process_function(func)
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def process_function(self, func):
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# defer removing those blocks, so our use checks will ignore deleted blocks
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preserve = [func.entry()]
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work_list = [func.entry()]
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while any(work_list):
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block = work_list.pop()
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for succ in block.successors():
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if succ not in preserve:
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preserve.append(succ)
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work_list.append(succ)
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to_be_removed = []
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for block in func.basic_blocks:
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if block not in preserve:
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block.is_removed = True
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to_be_removed.append(block)
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for insn in block.instructions:
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insn.is_removed = True
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for block in to_be_removed:
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self.remove_block(block)
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modified = True
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while modified:
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modified = False
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for insn in func.instructions():
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# Note that GetLocal is treated as an impure operation:
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# the local access validator has to observe it to emit
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# a diagnostic for reads of uninitialized locals, and
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# it also has to run after the interleaver, but interleaver
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# doesn't like to work with IR before DCE.
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if isinstance(insn, (ir.Phi, ir.Alloc, ir.GetAttr, ir.GetElem, ir.Coerce,
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ir.Arith, ir.Compare, ir.Select, ir.Quote, ir.Closure,
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ir.Offset)) \
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and not any(insn.uses):
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insn.erase()
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modified = True
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def remove_block(self, block):
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# block.uses are updated while iterating
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for use in set(block.uses):
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if use.is_removed:
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continue
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if isinstance(use, ir.Phi):
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use.remove_incoming_block(block)
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if not any(use.operands):
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self.remove_instruction(use)
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elif isinstance(use, ir.SetLocal):
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# setlocal %env, %block is only used for lowering finally
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use.erase()
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else:
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assert False
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block.erase()
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def remove_instruction(self, insn):
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for use in set(insn.uses):
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if use.is_removed:
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continue
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if isinstance(use, ir.Phi):
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use.remove_incoming_value(insn)
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if not any(use.operands):
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self.remove_instruction(use)
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else:
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assert False
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insn.erase()
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