[turbofan] Add --csa-verify flag that enables machine graph verification of code stubs.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index b7ce4c43538b9350d5adcf7a3d1b93890f57ba48..46af7d201929daa504cc596e57ee86d0391360ba 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -1762,10 +1762,19 @@ bool PipelineImpl::ScheduleAndSelectInstructions(Linkage* linkage,
         info(), data->graph(), data->schedule()));
   }
 
-  if (FLAG_turbo_verify_machine_graph != nullptr &&
-      (!strcmp(FLAG_turbo_verify_machine_graph, "*") ||
-       !strcmp(FLAG_turbo_verify_machine_graph,
-               data->info()->GetDebugName().get()))) {
+  bool verify_stub_graph =
+      DEBUG_BOOL && data->info()->IsStub() && (FLAG_csa_verify > 0);
+  // TODO(ishell): Always enable graph verification of stubs in debug mode
+  // once all the issues are fixed.
+  if (verify_stub_graph) {
+    // Enable graph verification for the first |FLAG_csa_verify| stubs.
+    --FLAG_csa_verify;

[Michael Starzinger, 2016/12/05 18:03:36]

suggestion: As discussed offline, this is not safe across multiple isolates
(i.e. the flag is per-process, but the pipeline is only synchronized
per-isolate). Could we copy out the initial value of FLAG_csa_verify into the
{Isolate} when it is initialized and then mutate that value instead (similar to
what we do to Heap::allocation_timeout for example)?

Or alternatively, have one cctest that sets the flag to a non-zero value, so
that we have full control over when this flag is set. We would just not support
to pass this flag via Chrome (or other embedders).

[Igor Sheludko, 2016/12/06 13:57:52]

I added the cctest.

+  }
+
+  if (verify_stub_graph || (FLAG_turbo_verify_machine_graph != nullptr &&
+                            (!strcmp(FLAG_turbo_verify_machine_graph, "*") ||
+                             !strcmp(FLAG_turbo_verify_machine_graph,
+                                     data->info()->GetDebugName().get())))) {
     Zone temp_zone(data->isolate()->allocator(), ZONE_NAME);
     MachineGraphVerifier::Run(data->graph(), data->schedule(), linkage,
                               &temp_zone);