From 2b8985608d33abaae7b201a008e292cbbe2167ef Mon Sep 17 00:00:00 2001
From: Matthew Sotoudeh <matthew@masot.net>
Date: Thu, 27 Jul 2023 14:26:33 -0700
Subject: add automated refcounting pass

---
 python/examples/refcounting/dietpass | 76 ++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100755 python/examples/refcounting/dietpass

(limited to 'python/examples/refcounting/dietpass')

diff --git a/python/examples/refcounting/dietpass b/python/examples/refcounting/dietpass
new file mode 100755
index 0000000..9a7b0e8
--- /dev/null
+++ b/python/examples/refcounting/dietpass
@@ -0,0 +1,76 @@
+#!/bin/python3
+import os
+import sys
+from dietc import *
+
+def eprint(*args): print(*args, file=sys.stderr)
+
+def main():
+    prog = Program(open(sys.argv[1], "rb").read())
+    prog.preamble.append("#include <refcounting.h>")
+    for function in prog.functions:
+        # (1) rewrite calloc, free, ... calls to refcount_*
+        for name in ("calloc", "free", "malloc", "realloc"):
+            function.body = [instr.replace_token(name, f"refcount_{name}")
+                             for instr in function.body]
+        new_body = function.body[:function.code_start()]
+        # (2a) initialize all pointer expressions to 0
+        for local in function.locals():
+            for p in ptr_exprs(local, prog.object_types[local]):
+                new_body.append(Instruction(f"{p} = 0 ;"))
+        # (2b) whenever a pointer is written to, call refcount_write
+        for instr in function.body[function.code_start():]:
+            if instr[0] == "*" and instr[2] == "=":
+                refcount_pairs = []
+                ty = prog.object_types[instr[1]].base
+                for expr in ptr_exprs(f"(*{instr[1]})", ty):
+                    backup = f"_refcount_ptr_backup_{count()}"
+                    new_body.append(Instruction(f"void * {backup} = {expr} ;"))
+                    refcount_pairs.append((backup, expr))
+                new_body.append(instr)
+                for old, new in refcount_pairs:
+                    new_body.append(Instruction(f"refcount_write({new},{old});"))
+            elif instr[1] == "=":
+                refcount_pairs = []
+                ty = prog.object_types[instr[0]]
+                for expr in ptr_exprs(instr[0], ty):
+                    backup = f"_refcount_ptr_backup_{count()}"
+                    new_body.append(Instruction(f"void * {backup} = {expr} ;"))
+                    refcount_pairs.append((backup, expr))
+                new_body.append(instr)
+                for old, new in refcount_pairs:
+                    new_body.append(Instruction(f"refcount_write({new},{old});"))
+            elif instr[0] == "return":
+                for local in function.locals():
+                    if local == instr[1]: continue
+                    for expr in ptr_exprs(local, prog.object_types[local]):
+                        new_body.append(Instruction(f"refcount_write(0,({expr}));"))
+                if instr[1] != ";":
+                    for expr in ptr_exprs(instr[1], prog.object_types[instr[1]]):
+                        new_body.append(Instruction(f"refcount_returning({expr});"))
+                new_body.append(instr)
+            else:
+                new_body.append(instr)
+        function.body = new_body
+    prog.print()
+
+# given an object and its type, returns a list of l-value expression strings,
+# representing all of the pointers in that object
+def ptr_exprs(name, ty):
+    if isinstance(ty, PointerType):
+        return [name]
+    elif isinstance(ty, AggregateType):
+        exprs = []
+        for fname, ftype in ty.fields:
+            exprs.extend(ptr_exprs(f"{name}.{fname}", ftype))
+        return exprs
+    elif isinstance(ty, (BasicType, FunctionType)):
+        return []
+    elif isinstance(ty, ArrayType):
+        # TODO
+        return []
+    else:
+        print(ty.classify(), file=sys.stderr)
+        raise NotImplementedError
+
+main()
-- 
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