[turbofan] Also run the CheckpointElimination as part of load elimination.

The LoadElimination (and potentially earlier passes too) might have
removed or lowered side-effecting operations, which allows for further
combining of check points in the graph, removing unnecessary StateValue
uses for the later truncation analysis.

BUG=chromium:709398
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2807563002
Cr-Commit-Position: refs/heads/master@{#44486}

src/compiler/pipeline.cc

@@ -1141,6 +1141,7 @@ struct LoadEliminationPhase {
     RedundancyElimination redundancy_elimination(&graph_reducer, temp_zone);
     LoadElimination load_elimination(&graph_reducer, data->jsgraph(),
                                      temp_zone);
+    CheckpointElimination checkpoint_elimination(&graph_reducer);
     ValueNumberingReducer value_numbering(temp_zone, data->graph()->zone());
     CommonOperatorReducer common_reducer(&graph_reducer, data->graph(),
                                          data->common(), data->machine());
@@ -1148,6 +1149,7 @@ struct LoadEliminationPhase {
     AddReducer(data, &graph_reducer, &dead_code_elimination);
     AddReducer(data, &graph_reducer, &redundancy_elimination);
     AddReducer(data, &graph_reducer, &load_elimination);
+    AddReducer(data, &graph_reducer, &checkpoint_elimination);
     AddReducer(data, &graph_reducer, &common_reducer);
     AddReducer(data, &graph_reducer, &value_numbering);
     graph_reducer.ReduceGraph();