Remove unused labels in O2

This update tried hard to remove unused
labels. Specially temporary ones.
User labels are left untouched.

If a several labels point to the same memory address
only the last one prevails, except when it's an user label.

If the last label is a temporary label and any other is
an user label, the latter will prevail.

Author: boriel

src/arch/zx48k/backend/__init__.py

@@ -2312,8 +2312,24 @@ def emit_end():
 
 
 def remove_unused_labels(output: List[str]):
-    labels_used: Set[str] = set()
+    labels_used: Dict[str, List[int]] = defaultdict(list)
     labels_to_delete: Dict[str, int] = {}
+    labels: Set[str] = set()
+    label_alias: Dict[str, str] = {}
+
+    prev = None
+    for i, ins in enumerate(output):
+        if ins and ins[-1] == ':':
+            ins = ins[:-1]
+            labels.add(ins)
+            if prev is not None:
+                if prev not in TMP_LABELS and ins in TMP_LABELS or prev in label_alias:
+                    label_alias[ins] = prev
+                else:
+                    label_alias[prev] = ins
+            prev = ins
+        else:
+            prev = None
 
     for i, ins in enumerate(output):
         try_label = ins[:-1]
@@ -2325,9 +2341,16 @@ def remove_unused_labels(output: List[str]):
             continue
 
         for op in Asm.opers(ins):
-            if op in TMP_LABELS:
-                labels_used.add(op)
-                labels_to_delete.pop(op, None)
+            if op in labels:
+                new_label = op
+                while new_label in label_alias:
+                    new_label = label_alias[new_label]
+
+                labels_used[new_label].append(i)
+                labels_to_delete.pop(new_label, None)
+
+                if new_label != op:
+                    output[i] = re.sub(r'\b' + op + r'\b', new_label, ins)
 
     for i in sorted(labels_to_delete.values(), reverse=True):
         output.pop(i)

src/arch/zx48k/optimizer/common.py

@@ -1,10 +1,14 @@
 # -*- config: utf-8 -*-
 
+from typing import Dict
+
+from . import labelinfo
+
 # counter for generating unique random fake values
 RAND_COUNT = 0
 
 # Labels which must start a basic block, because they're used in a JP/CALL
-LABELS = {}  # Label -> LabelInfo object
+LABELS: Dict[str, labelinfo.LabelInfo] = {}  # Label -> LabelInfo object
 
 JUMP_LABELS = set([])
 MEMORY = []  # Instructions emitted by the backend

src/arch/zx48k/optimizer/memcell.py

@@ -24,7 +24,7 @@ class MemCell:
 
     def __init__(self, instr: str, addr: int):
         self.addr = addr
-        self.asm = instr  # type: ignore
+        self.asm = instr
 
     @property
     def asm(self) -> Asm:
@@ -365,15 +365,4 @@ def replace_label(self, old_label: str, new_label: str):
         if old_label == new_label:
             return
 
-        tmp = re.compile(r'\b' + old_label + r'\b')
-        last = 0
-        l = len(new_label)
-
-        while True:
-            match = tmp.search(self.inst)
-            if not match:
-                break
-
-            txt = self.inst
-            self.asm = txt[:last + match.start()] + new_label + txt[last + match.end():]  # type: ignore
-            last += match.start() + l
+        self.asm = re.sub(r'\b' + old_label + r'\b', new_label, self.code)