[turbofan] Stand-alone deferred block splitting - full.

src/compiler/move-optimizer.cc

Index: src/compiler/move-optimizer.cc
diff --git a/src/compiler/move-optimizer.cc b/src/compiler/move-optimizer.cc
index b869185e60ed2aed9dbc939878d1874e92e4eda6..6d71ef2e1b6b0098bb8ee1f26979ffaaf3dbfafb 100644
--- a/src/compiler/move-optimizer.cc
+++ b/src/compiler/move-optimizer.cc
@@ -59,6 +59,14 @@ void MoveOptimizer::Run() {
   }
   for (auto block : code()->instruction_blocks()) {
     if (block->PredecessorCount() <= 1) continue;
+    bool has_only_deferred = true;
+    for (RpoNumber pred_id : block->predecessors()) {
+      if (!code()->InstructionBlockAt(pred_id)->IsDeferred()) {
+        has_only_deferred = false;
+        break;
+      }
+    }
+    if (has_only_deferred) continue;
     OptimizeMerge(block);
   }
   for (auto gap : to_finalize_) {