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Avoid generating value split instructions.

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The legalizer often splits values into parts with the vsplit and
isplit_lohi instructions. Avoid doing that for values that are already
defined by the corresponding concatenation instructions.

This reduces the number of instructions created during legalization, and
it simplifies later optimizations. A number of dead concatenation
instructions are left behind. They can be trivially cleaned up by a dead
code elimination pass.
This commit is contained in:
Jakob Stoklund Olesen
2017-03-21 13:25:08 -07:00
parent 2a321f42fb
commit 697246658d
5 changed files with 181 additions and 35 deletions
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71
lib/cretonne/meta/gen_legalizer.py
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@@ -9,7 +9,7 @@ the input instruction.
"""
from __future__ import absolute_import
from srcgen import Formatter
from base import legalize
from base import legalize, instructions
from cdsl.ast import Var
try:
@@ -117,36 +117,61 @@ def wrap_tup(seq):
return '({})'.format(', '.join(tup))
def is_value_split(node):
# type: (Def) -> bool
"""
Determine if `node` represents one of the value splitting instructions:
`isplit` or `vsplit. These instructions are lowered specially by the
`legalize::split` module.
"""
if len(node.defs) != 2:
return False
return node.expr.inst in (instructions.isplit, instructions.vsplit)
def emit_dst_inst(node, fmt):
# type: (Def, Formatter) -> None
exact_replace = False
replaced_inst = None # type: str
fixup_first_result = False
if len(node.defs) == 0:
# This node doesn't define any values, so just insert the new
# instruction.
builder = 'dfg.ins(pos)'
else:
src_def0 = node.defs[0].src_def
if src_def0 and node.defs[0] == src_def0.defs[0]:
# The primary result is replacing the primary result of the src
# pattern.
# Replace the whole instruction.
builder = 'let {} = dfg.replace(inst)'.format(wrap_tup(node.defs))
replaced_inst = 'inst'
# Secondary values weren't replaced if this is an exact replacement
# for all the src results.
exact_replace = (node.defs == src_def0.defs)
else:
# Insert a new instruction since its primary def doesn't match the
# src.
builder = 'let {} = dfg.ins(pos)'.format(wrap_tup(node.defs))
fixup_first_result = node.defs[0].is_output()
fmt.line('{}.{};'.format(builder, node.expr.rust_builder(node.defs)))
if is_value_split(node):
# Split instructions are not emitted with the builder, but by calling
# special functions in the `legalizer::split` module. These functions
# will eliminate concat-split patterns.
fmt.line(
'let {} = split::{}(dfg, pos, {});'
.format(
wrap_tup(node.defs),
node.expr.inst.snake_name(),
node.expr.args[0]))
else:
if len(node.defs) == 0:
# This node doesn't define any values, so just insert the new
# instruction.
builder = 'dfg.ins(pos)'
else:
src_def0 = node.defs[0].src_def
if src_def0 and node.defs[0] == src_def0.defs[0]:
# The primary result is replacing the primary result of the
# source pattern.
# Replace the whole instruction.
builder = 'let {} = dfg.replace(inst)'.format(
wrap_tup(node.defs))
replaced_inst = 'inst'
# Secondary values weren't replaced if this is an exact
# replacement for all the source results.
exact_replace = (node.defs == src_def0.defs)
else:
# Insert a new instruction since its primary def doesn't match
# the source.
builder = 'let {} = dfg.ins(pos)'.format(wrap_tup(node.defs))
fixup_first_result = node.defs[0].is_output()
fmt.line('{}.{};'.format(builder, node.expr.rust_builder(node.defs)))
# If we just replaced an instruction, we need to bump the cursor so
# following instructions are inserted *after* the replaced insruction.
# following instructions are inserted *after* the replaced instruction.
if replaced_inst:
with fmt.indented(
'if pos.current_inst() == Some({}) {{'