[turbofan] Ensure stackcheck flags do something.

src/compiler/pipeline.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/pipeline.h"
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
 
 #include "src/base/adapters.h"
@@ skipping 1342 matching lines @@
   if (FLAG_trace_turbo_graph) {
     OFStream os(stdout);
     PrintableInstructionSequence printable = {config, data->sequence()};
     os << "----- Instruction sequence before register allocation -----\n"
        << printable;
   }
   if (verifier != nullptr) {
     CHECK(!data->register_allocation_data()->ExistsUseWithoutDefinition());
   }
 
-  Run<SplinterLiveRangesPhase>();
+  if (FLAG_turbo_preprocess_ranges) {
+    Run<SplinterLiveRangesPhase>();
+  }
 
   // TODO(mtrofin): re-enable greedy once we have bots for range preprocessing.
   Run<AllocateGeneralRegistersPhase<LinearScanAllocator>>();
   Run<AllocateDoubleRegistersPhase<LinearScanAllocator>>();
 
-  Run<MergeSplintersPhase>();
+  if (FLAG_turbo_preprocess_ranges) {
+    Run<MergeSplintersPhase>();
+  }
 
   if (FLAG_turbo_frame_elision) {
     Run<LocateSpillSlotsPhase>();
     Run<FrameElisionPhase>();
   }
 
   Run<AssignSpillSlotsPhase>();
 
   Run<CommitAssignmentPhase>();
   Run<PopulateReferenceMapsPhase>();
@@ skipping 20 matching lines @@
     tcf << AsC1VRegisterAllocationData("CodeGen",
                                        data->register_allocation_data());
   }
 
   data->DeleteRegisterAllocationZone();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8