[compiler] Introduce --trace-code-dependencies

This is helpful for debugging. At the moment it reports any
installations of code dependencies and, by implying
--trace-deopt-verbose, any deopts due to dependency changes.

Change-Id: I910a6dc165cc3586eaf7e5f322c90924359ae6ba
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2519566
Auto-Submit: Georg Neis <neis@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70983}

src/deoptimizer/deoptimizer.cc

@@ -739,10 +739,10 @@ void Deoptimizer::TraceMarkForDeoptimization(Code code, const char* reason) {
 
   DeoptimizationData deopt_data = DeoptimizationData::cast(maybe_data);
   CodeTracer::Scope scope(isolate->GetCodeTracer());
-  PrintF(scope.file(), "[marking dependent code " V8PRIxPTR_FMT " ",
+  PrintF(scope.file(), "[marking dependent code " V8PRIxPTR_FMT " (",
          code.ptr());
   deopt_data.SharedFunctionInfo().ShortPrint(scope.file());
-  PrintF(" (opt id %d) for deoptimization, reason: %s]\n",
+  PrintF(") (opt id %d) for deoptimization, reason: %s]\n",
          deopt_data.OptimizationId().value(), reason);
   {
     AllowHeapAllocation yes_gc;

src/flags/flag-definitions.h

@@ -448,6 +448,10 @@ DEFINE_NEG_IMPLICATION(jitless, interpreted_frames_native_stack)
 DEFINE_BOOL(assert_types, false,
             "generate runtime type assertions to test the typer")
 
+DEFINE_BOOL(trace_code_dependencies, false, "trace code dependencies")
+// Depend on --trace-deopt-verbose for reporting dependency invalidations.
+DEFINE_IMPLICATION(trace_code_dependencies, trace_deopt_verbose)
+
 // Flags for experimental implementation features.
 DEFINE_BOOL(allocation_site_pretenuring, true,
             "pretenure with allocation sites")

src/objects/code.cc

@@ -943,6 +943,11 @@ void DependentCode::InstallDependency(Isolate* isolate,
                                       const MaybeObjectHandle& code,
                                       Handle<HeapObject> object,
                                       DependencyGroup group) {
+  if (V8_UNLIKELY(FLAG_trace_code_dependencies)) {
+    StdoutStream{} << "Installing dependency of [" << code->GetHeapObject()
+                   << "] on [" << object << "] in group ["
+                   << DependencyGroupName(group) << "]\n";
+  }
   Handle<DependentCode> old_deps(DependentCode::GetDependentCode(object),
                                  isolate);
   Handle<DependentCode> new_deps =

src/objects/code.h

@@ -641,7 +641,7 @@ class DependentCode : public WeakFixedArray {
     kAllocationSiteTransitionChangedGroup
   };
 
-  // Register a code dependency of {cell} on {object}.
+  // Register a dependency of {code} on {object}, of the kind given by {group}.
   V8_EXPORT_PRIVATE static void InstallDependency(Isolate* isolate,
                                                   const MaybeObjectHandle& code,
                                                   Handle<HeapObject> object,