340 lines
10 KiB
Python
340 lines
10 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 constant_hash import compute_quadratic
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from unique_table import UniqueSeqTable
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from collections import OrderedDict, defaultdict
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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('{} => {{'.format(instp.number), '}'):
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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 in instps:
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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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# Encoding lists are represented as u16 arrays.
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CODE_BITS = 16
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PRED_BITS = 12
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PRED_MASK = (1 << PRED_BITS) - 1
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# 0..CODE_ALWAYS means: Check instruction predicate and use the next two
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# entries as a (recipe, encbits) pair if true. CODE_ALWAYS is the always-true
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# predicate, smaller numbers refer to instruction predicates.
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CODE_ALWAYS = PRED_MASK
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# Codes above CODE_ALWAYS indicate an ISA predicate to be tested.
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# `x & PRED_MASK` is the ISA predicate number to test.
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# `(x >> PRED_BITS)*3` is the number of u16 table entries to skip if the ISA
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# predicate is false. (The factor of three corresponds to the (inst-pred,
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# recipe, encbits) triples.
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#
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# Finally, CODE_FAIL indicates the end of the list.
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CODE_FAIL = (1 << CODE_BITS) - 1
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def seq_doc(enc):
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"""
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Return a tuple containing u16 representations of the instruction predicate
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an recipe / encbits.
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Also return a doc string.
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"""
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if enc.instp:
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p = enc.instp.number
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doc = '--> {} when {}'.format(enc, enc.instp)
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else:
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p = CODE_ALWAYS
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doc = '--> {}'.format(enc)
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assert p <= CODE_ALWAYS
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return ((p, enc.recipe.number, enc.encbits), doc)
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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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name = self.inst.name
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if self.ty:
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name = '{}.{}'.format(name, self.ty.name)
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if self.encodings:
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name += ' ({})'.format(self.encodings[0].cpumode)
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return name
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def encode(self, seq_table, doc_table):
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"""
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Encode this list as a sequence of u16 numbers.
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Adds the sequence to `seq_table` and records the returned offset as
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`self.offset`.
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Adds comment lines to `doc_table` keyed by seq_table offsets.
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"""
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words = list()
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docs = list()
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for idx, enc in enumerate(self.encodings):
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seq, doc = seq_doc(enc)
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docs.append((len(words), doc))
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words.extend(seq)
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words.append(CODE_FAIL)
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self.offset = seq_table.add(words)
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# Add doc comments.
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doc_table[self.offset].append(
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'{:06x}: {}'.format(self.offset, self.name()))
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for pos, doc in docs:
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doc_table[self.offset + pos].append(doc)
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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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def layout_hashtable(self, level2_hashtables):
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"""
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Compute the hash table mapping opcode -> enclist.
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Append the hash table to `level2_hashtables` and record the offset.
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"""
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hash_table = compute_quadratic(
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self.lists.values(),
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lambda enclist: enclist.inst.number)
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self.hash_table_offset = len(level2_hashtables)
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self.hash_table_len = len(hash_table)
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level2_hashtables.extend(hash_table)
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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 encode_enclists(level1, seq_table, doc_table):
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"""
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Compute encodings and doc comments for encoding lists in `level1`.
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"""
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for level2 in level1:
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for enclist in level2:
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enclist.encode(seq_table, doc_table)
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def emit_enclists(seq_table, doc_table, fmt):
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with fmt.indented(
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'const ENCLISTS: [u16; {}] = ['.format(len(seq_table.table)),
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'];'):
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line = ''
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for idx, entry in enumerate(seq_table.table):
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if idx in doc_table:
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if line:
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fmt.line(line)
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line = ''
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for doc in doc_table[idx]:
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fmt.comment(doc)
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line += '{:#06x}, '.format(entry)
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if line:
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fmt.line(line)
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def encode_level2_hashtables(level1, level2_hashtables):
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for level2 in level1:
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level2.layout_hashtable(level2_hashtables)
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def emit_level2_hashtables(level2_hashtables, fmt):
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"""
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Emit the big concatenation of level 2 hash tables.
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"""
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with fmt.indented(
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'const LEVEL2: [(Opcode, u32); {}] = ['
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.format(len(level2_hashtables)),
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'];'):
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for entry in level2_hashtables:
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if entry:
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fmt.line(
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'(Opcode::{}, {:#08x}),'
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.format(entry.inst.camel_name, entry.offset))
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else:
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fmt.line('(Opcode::NotAnOpcode, 0),')
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def gen_isa(isa, 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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emit_instps(isa.all_instps, fmt)
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# Tables for enclists with comments.
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seq_table = UniqueSeqTable()
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doc_table = defaultdict(list)
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# Single table containing all the level2 hash tables.
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level2_hashtables = list()
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for cpumode in isa.cpumodes:
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level1 = make_tables(cpumode)
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encode_enclists(level1, seq_table, doc_table)
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encode_level2_hashtables(level1, level2_hashtables)
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emit_enclists(seq_table, doc_table, fmt)
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emit_level2_hashtables(level2_hashtables, fmt)
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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, fmt)
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fmt.update_file('encoding-{}.rs'.format(isa.name), out_dir)
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