From 21b4b4432a767408a0704a795e58fc577e69e530 Mon Sep 17 00:00:00 2001
From: Reid 'arrdem' McKenzie <me@arrdem.com>
Date: Sat, 2 Jul 2022 00:35:03 -0600
Subject: [PATCH] Slam out a two-pass assembler
---
.../shoggoth/src/python/ichor/__init__.py | 1 +
.../shoggoth/src/python/ichor/assembler.py | 62 +++++++++++++++++++
.../shoggoth/src/python/ichor/bootstrap.py | 1 +
.../test/python/ichor/test_assembler.py | 47 ++++++++++++++
4 files changed, 111 insertions(+)
create mode 100644 projects/shoggoth/src/python/ichor/assembler.py
create mode 100644 projects/shoggoth/test/python/ichor/test_assembler.py
diff --git a/projects/shoggoth/src/python/ichor/__init__.py b/projects/shoggoth/src/python/ichor/__init__.py
index 375fa7c..c30965d 100644
--- a/projects/shoggoth/src/python/ichor/__init__.py
+++ b/projects/shoggoth/src/python/ichor/__init__.py
@@ -10,3 +10,4 @@ from ichor.bootstrap import * # noqa
from ichor.impl import * # noqa
from ichor.isa import * # noqa
from ichor.typing import * # noqa
+from ichor.assembler import *
diff --git a/projects/shoggoth/src/python/ichor/assembler.py b/projects/shoggoth/src/python/ichor/assembler.py
new file mode 100644
index 0000000..dc47df3
--- /dev/null
+++ b/projects/shoggoth/src/python/ichor/assembler.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+
+from dataclasses import dataclass
+from random import choices
+from string import ascii_lowercase, digits
+from typing import List
+
+from ichor.isa import Opcode
+
+
+@dataclass
+class Label(object):
+ name: str
+
+ def __hash__(self):
+ return hash(self.name)
+
+class FuncBuilder(object):
+ def __init__(self) -> None:
+ self._opcodes = []
+
+ def write(self, op: Opcode):
+ self._opcodes.append(op)
+
+ def make_label(self, prefix=""):
+ frag = ''.join(choices(ascii_lowercase + digits, k=8))
+ return Label(f"{prefix or 'gensym'}_{frag}")
+
+ def set_label(self, label: Label):
+ self._opcodes.append(label)
+
+ def build(self) -> List[Opcode]:
+ """Assemble the written body into fully resolved opcodes."""
+
+ # The trivial two-pass assembler. First pass removes labels from the
+ # opcode stream, marking where they occurred.
+
+ labels = {}
+ unassembled = []
+ for op in self._opcodes:
+ match op:
+ case Label(_) as l:
+ assert l not in labels # Label marks must be unique.
+ labels[l] = len(unassembled)
+ case o:
+ unassembled.append(o)
+
+ # Second pass rewrites instructions (which can reference forwards OR
+ # backwards labels) with real targets instead of labels.
+ assembled = []
+ for op in unassembled:
+ match op:
+ case Opcode.GOTO(Label(_) as l):
+ assembled.append(Opcode.GOTO(labels[l]))
+
+ case Opcode.VTEST(Label(_) as l):
+ assembled.append(Opcode.VTEST(labels[l]))
+
+ case o:
+ assembled.append(o)
+
+ return assembled
diff --git a/projects/shoggoth/src/python/ichor/bootstrap.py b/projects/shoggoth/src/python/ichor/bootstrap.py
index d34b42f..40dc611 100644
--- a/projects/shoggoth/src/python/ichor/bootstrap.py
+++ b/projects/shoggoth/src/python/ichor/bootstrap.py
@@ -6,6 +6,7 @@ Hopefully no "real" interpreter ever uses this code, since it's obviously replac
from ichor.isa import Opcode
from ichor.state import Module, Variant
+from ichor.assembler import FuncBuilder
BOOTSTRAP = Module()
diff --git a/projects/shoggoth/test/python/ichor/test_assembler.py b/projects/shoggoth/test/python/ichor/test_assembler.py
new file mode 100644
index 0000000..c7deea5
--- /dev/null
+++ b/projects/shoggoth/test/python/ichor/test_assembler.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+from ichor import FuncBuilder, Opcode
+
+import pytest
+
+@pytest.fixture
+def builder() -> FuncBuilder:
+ return FuncBuilder()
+
+
+def test_forwards_label(builder: FuncBuilder):
+ l = builder.make_label()
+ builder.write(Opcode.GOTO(l))
+ builder.write(Opcode.DROP(0)) # no-op
+ builder.set_label(l)
+ builder.write(Opcode.DROP(0)) # no-op
+ instrs = builder.build()
+ assert instrs == [
+ Opcode.GOTO(2),
+ Opcode.DROP(0),
+ Opcode.DROP(0),
+ ]
+
+
+def test_backwards_label(builder: FuncBuilder):
+ l = builder.make_label()
+ builder.set_label(l)
+ builder.write(Opcode.DROP(0)) # no-op
+ builder.write(Opcode.GOTO(l))
+ instrs = builder.build()
+ assert instrs == [
+ Opcode.DROP(0),
+ Opcode.GOTO(0),
+ ]
+
+
+def test_self_label(builder: FuncBuilder):
+ l = builder.make_label()
+ builder.write(Opcode.DROP(0)) # no-op
+ builder.set_label(l)
+ builder.write(Opcode.GOTO(l))
+ instrs = builder.build()
+ assert instrs == [
+ Opcode.DROP(0),
+ Opcode.GOTO(1),
+ ]