[turbofan] Don't eliminate FinishRegion nodes.

src/compiler/typed-optimization.cc

Index: src/compiler/typed-optimization.cc
diff --git a/src/compiler/typed-optimization.cc b/src/compiler/typed-optimization.cc
index 4fef5323e4e1c9bef51d4cad907aaaf6adbf0203..5a6e4d7647a3c9bb61a5ca457ad38a42b7c29aec 100644
--- a/src/compiler/typed-optimization.cc
+++ b/src/compiler/typed-optimization.cc
@@ -33,6 +33,10 @@ Reduction TypedOptimization::Reduce(Node* node) {
   // result value and can simply replace the node if it's eliminable.
   if (!NodeProperties::IsConstant(node) && NodeProperties::IsTyped(node) &&
       node->op()->HasProperty(Operator::kEliminatable)) {
+    // TODO(v8:5303): We must not eliminate FinishRegion here. This special
+    // case can be removed once we have separate operators for value and
+    // effect regions.
+    if (node->opcode() == IrOpcode::kFinishRegion) return NoChange();
     // We can only constant-fold nodes here, that are known to not cause any
     // side-effect, may it be a JavaScript observable side-effect or a possible
     // eager deoptimization exit (i.e. {node} has an operator that doesn't have