[turbofan] Fix GVN of projections and add verification for projection uniqueness.

src/compiler/verifier.cc

Index: src/compiler/verifier.cc
diff --git a/src/compiler/verifier.cc b/src/compiler/verifier.cc
index 348e09059541ce1ed09228d41ad55f3921a2759c..534b68441494c30a0ad338edef9328576fdbb533 100644
--- a/src/compiler/verifier.cc
+++ b/src/compiler/verifier.cc
@@ -825,7 +825,23 @@ void Verifier::Run(Graph* graph, Typing typing) {
   CHECK_NOT_NULL(graph->end());
   Zone zone;
   Visitor visitor(&zone, typing);
-  for (Node* node : AllNodes(&zone, graph).live) visitor.Check(node);
+  AllNodes all(&zone, graph);
+  for (Node* node : all.live) visitor.Check(node);
+
+  // Check the uniqueness of projections.
+  for (Node* proj : all.live) {
+    if (proj->opcode() != IrOpcode::kProjection) continue;
+    Node* node = proj->InputAt(0);
+    for (Node* other : node->uses()) {
+      if (all.IsLive(other) && other != proj &&
+          other->opcode() == IrOpcode::kProjection &&
+          ProjectionIndexOf(other->op()) == ProjectionIndexOf(proj->op())) {
+        V8_Fatal(__FILE__, __LINE__,
+                 "Node #%d:%s has duplicate projections #%d and #%d",
+                 node->id(), node->op()->mnemonic(), proj->id(), other->id());
+      }
+    }
+  }
 }