0c6e0e9cb7
Amend build script to generate an encodings-<isa>.rs file for each target ISA. Emit a function that can evaluate instruction predicates. Describe the 3-level tables used for representing insrruction encoding tables. Add Python classes representing the tables. The generated code is incomplete and not used anywhere yet.
213 lines
6.5 KiB
Python
213 lines
6.5 KiB
Python
"""
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Generate sources for instruction encoding.
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The tables and functions generated here support the `TargetIsa::encode()`
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function which determines if a given instruction is legal, and if so, it's
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`Encoding` data which consists of a *recipe* and some *encoding* bits.
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The `encode` function doesn't actually generate the binary machine bits. Each
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recipe has a corresponding hand-written function to do that after registers
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are allocated.
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This is the information available to us:
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- The instruction to be encoded as an `Inst` reference.
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- The data-flow graph containing the instruction, giving us access to the
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`InstructionData` representation and the types of all values involved.
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- A target ISA instance with shared and ISA-specific settings for evaluating
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ISA predicates.
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- The currently active CPU mode is determined by the ISA.
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## Level 1 table lookup
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The CPU mode provides the first table. The key is the instruction's controlling
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type variable. If the instruction is not polymorphic, use `VOID` for the type
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variable. The table values are level 2 tables.
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## Level 2 table lookup
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The level 2 table is keyed by the instruction's opcode. The table values are
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*encoding lists*.
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The two-level table lookup allows the level 2 tables to be much smaller with
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good locality. Code in any given function usually only uses a few different
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types, so many of the level 2 tables will be cold.
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## Encoding lists
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An encoding list is a non-empty sequence of list entries. Each entry has
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one of these forms:
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1. Instruction predicate, encoding recipe, and encoding bits. If the
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instruction predicate is true, use this recipe and bits.
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2. ISA predicate and skip-count. If the ISA predicate is false, skip the next
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*skip-count* entries in the list. If the skip count is zero, stop
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completely.
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3. Stop. End of list marker. If this is reached, the instruction does not have
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a legal encoding.
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The instruction predicate is also used to distinguish between polymorphic
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instructions with different types for secondary type variables.
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"""
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from __future__ import absolute_import
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import srcgen
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from collections import OrderedDict
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def emit_instp(instp, fmt):
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"""
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Emit code for matching an instruction predicate against an
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`InstructionData` reference called `inst`.
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The generated code is a pattern match that falls through if the instruction
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has an unexpected format. This should lead to a panic.
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"""
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iform = instp.predicate_context()
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# Which fiels do we need in the InstructionData pattern match?
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if iform.boxed_storage:
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fields = 'ref data'
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else:
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# Collect the leaf predicates
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leafs = set()
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instp.predicate_leafs(leafs)
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# All the leafs are FieldPredicate instances. Here we just care about
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# the field names.
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fields = ', '.join(sorted(set(p.field.name for p in leafs)))
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with fmt.indented(
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'if let {} {{ {}, .. }} = *inst {{'
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.format(iform.name, fields), '}'):
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fmt.line('return {};'.format(instp.rust_predicate(0)))
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def emit_instps(instps, fmt):
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"""
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Emit a function for matching instruction predicates.
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"""
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with fmt.indented(
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'fn check_instp(inst: &InstructionData, instp_idx: u16) -> bool {',
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'}'):
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with fmt.indented('match instp_idx {', '}'):
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for (instp, idx) in instps.items():
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with fmt.indented('{} => {{'.format(idx), '}'):
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emit_instp(instp, fmt)
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fmt.line('_ => panic!("Invalid instruction predicate")')
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# The match cases will fall through if the instruction format is wrong.
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fmt.line('panic!("Bad format {}/{} for instp {}",')
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fmt.line(' InstructionFormat::from(inst),')
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fmt.line(' inst.opcode(),')
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fmt.line(' instp_idx);')
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def collect_instps(cpumodes):
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# Map instp -> number
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instps = OrderedDict()
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for cpumode in cpumodes:
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for enc in cpumode.encodings:
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instp = enc.instp
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if instp and instp not in instps:
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instps[instp] = 1 + len(instps)
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return instps
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class EncList(object):
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"""
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List of instructions for encoding a given type + opcode pair.
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An encoding list contains a sequence of predicates and encoding recipes,
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all encoded as u16 values.
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:param inst: The instruction opcode being encoded.
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:param ty: Value of the controlling type variable, or `None`.
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"""
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def __init__(self, inst, ty):
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self.inst = inst
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self.ty = ty
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# List of applicable Encoding instances.
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# These will have different predicates.
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self.encodings = []
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def name(self):
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if self.ty:
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return '{}.{}'.format(self.inst.name, self.ty.name)
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else:
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return self.inst.name
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class Level2Table(object):
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"""
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Level 2 table mapping instruction opcodes to `EncList` objects.
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:param ty: Controlling type variable of all entries, or `None`.
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"""
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def __init__(self, ty):
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self.ty = ty
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# Maps inst -> EncList
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self.lists = OrderedDict()
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def __getitem__(self, inst):
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ls = self.lists.get(inst)
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if not ls:
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ls = EncList(inst, self.ty)
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self.lists[inst] = ls
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return ls
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def __iter__(self):
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return iter(self.lists.values())
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class Level1Table(object):
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"""
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Level 1 table mapping types to `Level2` objects.
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"""
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def __init__(self):
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self.tables = OrderedDict()
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def __getitem__(self, ty):
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tbl = self.tables.get(ty)
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if not tbl:
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tbl = Level2Table(ty)
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self.tables[ty] = tbl
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return tbl
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def __iter__(self):
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return iter(self.tables.values())
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def make_tables(cpumode):
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"""
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Generate tables for `cpumode` as described above.
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"""
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table = Level1Table()
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for enc in cpumode.encodings:
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ty = enc.ctrl_typevar()
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inst = enc.inst
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table[ty][inst].encodings.append(enc)
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return table
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def gen_isa(cpumodes, fmt):
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# First assign numbers to relevant instruction predicates and generate the
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# check_instp() function..
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instps = collect_instps(cpumodes)
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emit_instps(instps, fmt)
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for cpumode in cpumodes:
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level1 = make_tables(cpumode)
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for level2 in level1:
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for enclist in level2:
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fmt.comment(enclist.name())
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def generate(isas, out_dir):
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for isa in isas:
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fmt = srcgen.Formatter()
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gen_isa(isa.cpumodes, fmt)
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fmt.update_file('encoding-{}.rs'.format(isa.name), out_dir)
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