minor improvements to rewrite (#12454)

* minor improvements to rewrite

* need that continue

* faster

tinygrad/uop/__init__.py

@@ -10,6 +10,7 @@ class FastEnum(IntEnum):
 class Ops(FastEnum):
   # uops that aren't rendered
   NOOP = auto(); SINK = auto(); UNIQUE = auto(); DEVICE = auto(); KERNEL = auto(); PRECAST = auto(); REWRITE_ERROR = auto()  # noqa: E702
+  SENTINEL = auto()
 
   # track children
   CHILD = auto(); CHILDREN = auto() # noqa: E702

tinygrad/uop/ops.py

@@ -1023,6 +1023,7 @@ if TRACK_MATCH_STATS or PROFILE:
 
 # *** simple graph rewrite engine ***
 
+SENTINEL = UOp(Ops.SENTINEL)
 class RewriteNotReady(Exception): pass
 class BottomUpGate(Exception): pass
 class RewriteContext:
@@ -1035,45 +1036,58 @@ class RewriteContext:
     self.replace: dict[UOp, UOp] = {}
 
   def cached_pm_rewrite(self, x:UOp):
-    if (ret:=self.pm_cache.get(x,False)) is not False: return ret
+    if (ret:=self.pm_cache.get(x,SENTINEL)) is not SENTINEL: return ret
     ret = self.pm_cache[x] = cast(PatternMatcher, self.pm).rewrite(x, self.ctx)
     return ret
 
   def cached_bpm_rewrite(self, x:UOp):
-    if (ret:=self.bpm_cache.get(x,False)) is not False: return ret
+    if (ret:=self.bpm_cache.get(x,SENTINEL)) is not SENTINEL: return ret
     ret = self.bpm_cache[x] = cast(PatternMatcher, self.bpm).rewrite(x, self.ctx)
     return ret
 
   def unified_rewrite(self, root:UOp) -> UOp:
     stack: collections.deque[tuple[UOp, int, UOp]] = collections.deque([(root, 0, root)])
     on_stack = {root}  # all UOps either on the stack or in self.replace, i.e. dont have to be placed again
+    REWRITE_STACK_LIMIT = getenv("REWRITE_STACK_LIMIT", 250000)
     while stack:
-      if len(stack) > getenv("REWRITE_STACK_LIMIT", 250000): raise RuntimeError("infinite loop in graph_rewrite (stack too big)")
+      if len(stack) > REWRITE_STACK_LIMIT: raise RuntimeError("infinite loop in graph_rewrite (stack too big)")
       n, stage, new_n = stack.pop()
       if n in self.replace: continue  # skip any nodes we have seen
-      try:
-        if stage == 0:
+      if stage == 0:
+        # if bottom up, we rewrite this node early. in both cases, we add its parents to the stack
+        if self.bpm is not None:
+          # apply rewrite rules until a fixed point is reached. may return `uop` itself if PatternMatcher doesn't match
+          test_n: UOp|None = n
+          seen = set()
           try:
-            # if bottom up, we rewrite this node early. in both cases, we add its parents to the stack
-            if self.bpm is not None:
-              # apply rewrite rules until a fixed point is reached. may return `uop` itself if PatternMatcher doesn't match
-              test_n: UOp|None = n
-              seen = set()
-              while test_n is not None:
-                if test_n in seen: raise RuntimeError("infinite loop in fixed_point_rewrite")
-                seen.add(test_n)
-                new_n, test_n = test_n, self.cached_bpm_rewrite(test_n)
-            stack.append((n, 1, new_n))
-            for x in reversed(new_n.src):
-              if x in on_stack: continue
-              stack.append((x, 0, x))
-              on_stack.add(x)
-          # if the bpm matching raised a gate, we are done with this node and dont continue down the srcs
-          except BottomUpGate: self.replace[n] = new_n
-        elif stage == 1:
-          try: new_src = tuple([self.replace[x] for x in new_n.src])
-          except KeyError: raise RewriteNotReady
-          if new_src == new_n.src:
+            while test_n is not None:
+              if test_n in seen: raise RuntimeError("infinite loop in fixed_point_rewrite")
+              seen.add(test_n)
+              new_n, test_n = test_n, self.cached_bpm_rewrite(test_n)
+          except RewriteNotReady:
+            # try the full thing again later
+            stack.appendleft((n, 0, n))
+            continue
+          except BottomUpGate:
+            # if the bpm matching raised a gate, we are done with this node and dont continue down the srcs
+            self.replace[n] = new_n
+            continue
+        stack.append((n, 1, new_n))
+        for x in reversed(new_n.src):
+          if x in on_stack: continue
+          stack.append((x, 0, x))
+          on_stack.add(x)
+      elif stage == 1:
+        tmp = []
+        for x in new_n.src:
+          if (rx:=self.replace.get(x, SENTINEL)) is SENTINEL:
+            # if some new sources aren't ready, we try this again later
+            stack.appendleft((n, 1, new_n))
+            break
+          tmp.append(rx)
+        else:
+          # in stage 1, once all srcs are rewritten, rebuild (if changed) or run top-down rewrite
+          if (new_src:=tuple(tmp)) == new_n.src:
             # if top down, do the rewrite. if no rewrite or bottom up, we are done rewriting this node so we add it to the dict
             if self.pm is None or (new_src_n:=self.cached_pm_rewrite(new_n)) is None:
               self.replace[n] = new_n
@@ -1084,13 +1098,14 @@ class RewriteContext:
           # trigger a rewrite of new_src_n, then after that rewrite is done, link it back to n
           stack.append((n, 2, new_src_n))
           stack.append((new_src_n, 0, new_src_n))
+      else:
+        # in stage 2, we link the result of new_n to the result of n
+        if (replaced_new_n:=self.replace.get(new_n, SENTINEL)) is SENTINEL:
+          # not ready, try the link later
+          stack.appendleft((n, 2, new_n))
         else:
-          # in stage 2, we link the result of new_n to the result of n
-          try: self.replace[n] = self.replace[new_n]
-          except KeyError: raise RewriteNotReady
-      except RewriteNotReady:
-        # retry this later
-        stack.appendleft((n, stage, new_n))
+          # otherwise we are done
+          self.replace[n] = replaced_new_n
     return self.replace[root]
 
 @track_matches