Aaron/lesson3 tasks

compiler/cfg.py

@@ -0,0 +1,53 @@
+import json
+import sys
+
+TERMINATORS = {'jmp', 'br', 'ret'}
+
+
+def make_blocks(body):
+    cur_block = []
+    for instr in body:
+        if 'op' in instr:
+            cur_block.append(instr)
+            if instr['op'] in TERMINATORS:
+                if cur_block: yield cur_block
+                cur_block = []
+        elif 'label' in instr:
+            if cur_block: yield cur_block
+            cur_block = [instr]
+        else:
+            assert False, f"{instr} has neither an op nor label"
+    if cur_block: yield cur_block
+
+
+def name_blocks(blocks):
+    named_blocks = []
+    for block in blocks:
+        name = f"b{len(named_blocks)}"
+        print(block)
+        if 'label' in block[0]:
+            name = block[0]['label']
+        named_blocks.append((name, block))
+    return named_blocks
+
+
+def make_cfg():
+    prog = json.load(sys.stdin)
+    cfg = {}
+    for func in prog['functions']:
+        named_blocks = name_blocks(make_blocks(func['instrs']))
+        for i, (name, block) in enumerate(named_blocks):
+            if 'op' in block[-1] and block[-1]['op'] in {'jmp', 'br'}:
+                cfg[name] = block[-1]['labels']
+            elif 'op' in block[-1] and block[-1]['op'] == 'ret':
+                cfg[name] = []
+            else:
+                if i + 1 < len(named_blocks):
+                    cfg[name] = [named_blocks[i+1][0]]
+                else:
+                    cfg[name] = []
+    print(cfg)
+
+
+if __name__ == "__main__":
+    make_cfg()

compiler/dce.py

@@ -0,0 +1,58 @@
+import json
+import sys
+from cfg import make_blocks
+
+
+def eliminate_unused_vars(instructions):
+    used_variables = set()
+    for instr in instructions:
+        if 'args' in instr:
+            for var in instr['args']:
+                used_variables.add(var)
+
+    for i, instr in enumerate(instructions):
+        if 'dest' in instr and instr['dest'] not in used_variables:
+            print(f"Deleting {instr}", file=sys.stderr)
+            instructions.remove(instr)
+
+    return instructions
+
+
+def eliminate_redundant_assigns_in_basic_block(block):
+    assigned_but_unused = {}
+    for i, instr in enumerate(block):
+        if 'args' in instr:
+            for arg in instr['args']:
+                if arg in assigned_but_unused:
+                    del assigned_but_unused[arg]
+        if 'dest' in instr:
+            if instr['dest'] in assigned_but_unused:
+                del block[assigned_but_unused[instr['dest']]]
+            assigned_but_unused[instr['dest']] = i
+
+
+def do_dce():
+    prog = json.load(sys.stdin)
+    for func in prog['functions']:
+        # Eliminate everything which just doesn't get used
+        old_len = 0
+        while len(func['instrs']) != old_len:
+            old_len = len(func['instrs'])
+            func['instrs'] = eliminate_unused_vars(func['instrs'])
+
+        # Eliminate everything which gets reassigned before use
+        blocks = make_blocks(func['instrs'])
+        instructions = []
+        for block in blocks:
+            old_len = 0
+            while len(block) != old_len:
+                old_len = len(block)
+                eliminate_redundant_assigns_in_basic_block(block)
+            instructions.extend(block)
+        func['instrs'] = instructions
+
+    print(json.dumps(prog))
+
+
+if __name__ == '__main__':
+    do_dce()