[turbofan] Do not map nodes to the same path state

In {ControlPathState} with {kMultipleInstances}, a node should be able
to be mapped to different states, but not twice to an identical state.

Change-Id: Ida340a6f4f5e891f586d5a90e7ae818f24dfbe98
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3769693
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81775}

src/compiler/control-path-state.h

@@ -135,7 +135,11 @@ template <typename NodeState, NodeUniqueness node_uniqueness>
 void ControlPathState<NodeState, node_uniqueness>::AddState(
     Zone* zone, Node* node, NodeState state,
     ControlPathState<NodeState, node_uniqueness> hint) {
-  if (node_uniqueness == kUniqueInstance && LookupState(node).IsSet()) return;
+  NodeState previous_state = LookupState(node);
+  if (node_uniqueness == kUniqueInstance ? previous_state.IsSet()
+                                         : previous_state == state) {
+    return;
+  }
 
   FunctionalList<NodeState> prev_front = blocks_.Front();
   if (hint.blocks_.Size() > 0) {
@@ -153,7 +157,9 @@ template <typename NodeState, NodeUniqueness node_uniqueness>
 void ControlPathState<NodeState, node_uniqueness>::AddStateInNewBlock(
     Zone* zone, Node* node, NodeState state) {
   FunctionalList<NodeState> new_block;
-  if (node_uniqueness == kMultipleInstances || !LookupState(node).IsSet()) {
+  NodeState previous_state = LookupState(node);
+  if (node_uniqueness == kUniqueInstance ? !previous_state.IsSet()
+                                         : previous_state != state) {
     new_block.PushFront(state, zone);
     states_.Set({node, depth(blocks_.Size() + 1)}, state);
   }