[cleanup] Stop using the now-unused deopt_count from feedback vector.

Unfortunately, we still have to keep the field because GC mole and Torque
do not support platform specific padding well
(see http://crbug.com/v8/9287).

Bug: v8:9183
Change-Id: I2210be4b8174c97bc82145605f9b862aac3bdc37
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624791Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61802}

src/builtins/base.tq

@@ -1277,7 +1277,10 @@ extern class FeedbackVector extends HeapObject {
   length: int32;
   invocation_count: int32;
   profiler_ticks: int32;
-  deopt_count: int32;
+  // TODO(v8:9287) The padding is not necessary on platforms with 4 bytes
+  // tagged pointers, we should make it conditional; however, platform-specific
+  // interacts badly with GCMole, so we need to address that first.
+  padding: uint32;
 }
 
 extern class FeedbackCell extends Struct {

src/deoptimizer/deoptimizer.cc

@@ -429,7 +429,6 @@ void Deoptimizer::DeoptimizeFunction(JSFunction function, Code code) {
     function.feedback_vector().EvictOptimizedCodeMarkedForDeoptimization(
         function.shared(), "unlinking code marked for deopt");
     if (!code.deopt_already_counted()) {
-      function.feedback_vector().increment_deopt_count();
       code.set_deopt_already_counted(true);
     }
     DeoptimizeMarkedCodeForContext(function.context().native_context());
@@ -493,19 +492,10 @@ Deoptimizer::Deoptimizer(Isolate* isolate, JSFunction function,
   DCHECK(AllowHeapAllocation::IsAllowed());
   disallow_heap_allocation_ = new DisallowHeapAllocation();
 #endif  // DEBUG
-  if (compiled_code_.kind() != Code::OPTIMIZED_FUNCTION ||
-      !compiled_code_.deopt_already_counted()) {
-    // If the function is optimized, and we haven't counted that deopt yet, then
-    // increment the function's deopt count so that we can avoid optimising
-    // functions that deopt too often.
-
-    if (deopt_kind_ == DeoptimizeKind::kSoft) {
-      // Soft deopts shouldn't count against the overall deoptimization count
-      // that can eventually lead to disabling optimization for a function.
-      isolate->counters()->soft_deopts_executed()->Increment();
-    } else if (!function.is_null()) {
-      function.feedback_vector().increment_deopt_count();
-    }
+  if ((compiled_code_.kind() != Code::OPTIMIZED_FUNCTION ||
+       !compiled_code_.deopt_already_counted()) &&
+      deopt_kind_ == DeoptimizeKind::kSoft) {
+    isolate->counters()->soft_deopts_executed()->Increment();
   }
   if (compiled_code_.kind() == Code::OPTIMIZED_FUNCTION) {
     compiled_code_.set_deopt_already_counted(true);

src/heap/factory.cc

@@ -525,7 +525,7 @@ Handle<FeedbackVector> Factory::NewFeedbackVector(
   vector->set_length(length);
   vector->set_invocation_count(0);
   vector->set_profiler_ticks(0);
-  vector->set_deopt_count(0);
+  vector->clear_padding();
   vector->set_closure_feedback_cell_array(*closure_feedback_cell_array);
 
   // TODO(leszeks): Initialize based on the feedback metadata.

src/objects/feedback-vector-inl.h

@@ -108,7 +108,13 @@ ACCESSORS(FeedbackVector, closure_feedback_cell_array, ClosureFeedbackCellArray,
 INT32_ACCESSORS(FeedbackVector, length, kLengthOffset)
 INT32_ACCESSORS(FeedbackVector, invocation_count, kInvocationCountOffset)
 INT32_ACCESSORS(FeedbackVector, profiler_ticks, kProfilerTicksOffset)
-INT32_ACCESSORS(FeedbackVector, deopt_count, kDeoptCountOffset)
+
+void FeedbackVector::clear_padding() {
+  if (FIELD_SIZE(kPaddingOffset) == 0) return;
+  DCHECK_EQ(4, FIELD_SIZE(kPaddingOffset));
+  memset(reinterpret_cast<void*>(address() + kPaddingOffset), 0,
+         FIELD_SIZE(kPaddingOffset));
+}
 
 bool FeedbackVector::is_empty() const { return length() == 0; }
 
@@ -118,13 +124,6 @@ FeedbackMetadata FeedbackVector::metadata() const {
 
 void FeedbackVector::clear_invocation_count() { set_invocation_count(0); }
 
-void FeedbackVector::increment_deopt_count() {
-  int count = deopt_count();
-  if (count < std::numeric_limits<int32_t>::max()) {
-    set_deopt_count(count + 1);
-  }
-}
-
 Code FeedbackVector::optimized_code() const {
   MaybeObject slot = optimized_code_weak_or_smi();
   DCHECK(slot->IsSmi() || slot->IsWeakOrCleared());

src/objects/feedback-vector.cc

@@ -246,7 +246,6 @@ Handle<FeedbackVector> FeedbackVector::New(
                                    : OptimizationMarker::kNone)));
   DCHECK_EQ(vector->invocation_count(), 0);
   DCHECK_EQ(vector->profiler_ticks(), 0);
-  DCHECK_EQ(vector->deopt_count(), 0);
 
   // Ensure we can skip the write barrier
   Handle<Object> uninitialized_sentinel = UninitializedSentinel(isolate);
@@ -368,7 +367,6 @@ void FeedbackVector::EvictOptimizedCodeMarkedForDeoptimization(
       PrintF("]\n");
     }
     if (!code.deopt_already_counted()) {
-      increment_deopt_count();
       code.set_deopt_already_counted(true);
     }
     ClearOptimizedCode();

src/objects/feedback-vector.h

@@ -204,15 +204,14 @@ class FeedbackVector : public HeapObject {
   // [invocation_count]: The number of times this function has been invoked.
   DECL_INT32_ACCESSORS(invocation_count)
 
-  // [invocation_count]: The number of times this function has been seen by the
+  // [profiler_ticks]: The number of times this function has been seen by the
   // runtime profiler.
   DECL_INT32_ACCESSORS(profiler_ticks)
 
-  // [deopt_count]: The number of times this function has deoptimized.
-  DECL_INT32_ACCESSORS(deopt_count)
+  // Initialize the padding if necessary.
+  inline void clear_padding();
 
   inline void clear_invocation_count();
-  inline void increment_deopt_count();
 
   inline Code optimized_code() const;
   inline OptimizationMarker optimization_marker() const;
@@ -315,9 +314,10 @@ class FeedbackVector : public HeapObject {
   DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize,
                                 TORQUE_GENERATED_FEEDBACK_VECTOR_FIELDS)
 
-  static constexpr int kUnalignedHeaderSize = kSize;
-  static const int kHeaderSize =
-      RoundUp<kObjectAlignment>(int{kUnalignedHeaderSize});
+  static const int kHeaderSize = kSize;
+
+  static_assert(kSize % kObjectAlignment == 0,
+                "Header must be padded for alignment");
   static const int kFeedbackSlotsOffset = kHeaderSize;
 
   class BodyDescriptor;

src/runtime/runtime-test.cc

@@ -572,15 +572,6 @@ RUNTIME_FUNCTION(Runtime_UnblockConcurrentRecompilation) {
   return ReadOnlyRoots(isolate).undefined_value();
 }
 
-RUNTIME_FUNCTION(Runtime_GetDeoptCount) {
-  HandleScope scope(isolate);
-  DCHECK_EQ(1, args.length());
-  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
-  // Functions without a feedback vector have never deoptimized.
-  if (!function->has_feedback_vector()) return Smi::kZero;
-  return Smi::FromInt(function->feedback_vector().deopt_count());
-}
-
 static void ReturnThis(const v8::FunctionCallbackInfo<v8::Value>& args) {
   args.GetReturnValue().Set(args.This());
 }

src/runtime/runtime.h

@@ -444,7 +444,6 @@ namespace internal {
   F(DisassembleFunction, 1, 1)                \
   F(FreezeWasmLazyCompilation, 1, 1)          \
   F(GetCallable, 0, 1)                        \
-  F(GetDeoptCount, 1, 1)                      \
   F(GetInitializerFunction, 1, 1)             \
   F(GetOptimizationStatus, -1, 1)             \
   F(GetUndetectable, 0, 1)                    \

test/mjsunit/compiler/native-context-specialization-hole-check.js

@@ -48,4 +48,4 @@ g();
 g();
 %OptimizeFunctionOnNextCall(g);
 g();
-assertTrue(%GetDeoptCount(g) > 0);
+assertUnoptimized(g);

test/mjsunit/deopt-recursive-eager-once.js

@@ -16,8 +16,6 @@ function foo(i, deopt = false) {
 }
 %PrepareFunctionForOptimization(foo);
 
-assertEquals(0, %GetDeoptCount(foo));
-
 %PrepareFunctionForOptimization(foo);
 foo(10);
 foo(10);
@@ -25,9 +23,7 @@ foo(10);
 foo(10);
 
 assertOptimized(foo);
-assertEquals(0, %GetDeoptCount(foo));
 
 foo(10, true);
 
 assertUnoptimized(foo);
-assertEquals(1, %GetDeoptCount(foo));

test/mjsunit/deopt-recursive-lazy-once.js

@@ -17,16 +17,13 @@ function foo(i, deopt = false) {
 %PrepareFunctionForOptimization(foo);
 
 %PrepareFunctionForOptimization(foo);
-assertEquals(0, %GetDeoptCount(foo));
 foo(10);
 foo(10);
 %OptimizeFunctionOnNextCall(foo);
 foo(10);
 
 assertOptimized(foo);
-assertEquals(0, %GetDeoptCount(foo));
 
 foo(10, true);
 
 assertUnoptimized(foo);
-assertEquals(1, %GetDeoptCount(foo));

test/mjsunit/deopt-recursive-soft-once.js

@@ -16,8 +16,6 @@ function foo(i, deopt = false, deoptobj = null) {
     }
 }
 
-assertEquals(0, %GetDeoptCount(foo));
-
 %PrepareFunctionForOptimization(foo);
 foo(10);
 foo(10);
@@ -25,10 +23,7 @@ foo(10);
 foo(10);
 
 assertOptimized(foo);
-assertEquals(0, %GetDeoptCount(foo));
 
 foo(10, true, { bar: function(){} });
 
 assertUnoptimized(foo);
-// Soft deopts don't count to the deopt count.
-assertEquals(0, %GetDeoptCount(foo));

test/mjsunit/deopt-unlinked.js

@@ -9,23 +9,18 @@
 
 function foo() {}
 
-assertEquals(0, %GetDeoptCount(foo));
-
 foo();
 foo();
 %OptimizeFunctionOnNextCall(foo);
 foo();
 
 assertOptimized(foo);
-assertEquals(0, %GetDeoptCount(foo));
 
 // Unlink the function.
 %DeoptimizeFunction(foo);
 
 assertUnoptimized(foo);
-assertEquals(1, %GetDeoptCount(foo));
 
 foo();
 
 assertUnoptimized(foo);
-assertEquals(1, %GetDeoptCount(foo));

test/mjsunit/regress/regress-crbug-937734.js

@@ -2,15 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax
+// Flags: --allow-natives-syntax --opt
 
 function foo()
 {
     return 1 in [0];
 }
 
+%PrepareFunctionForOptimization(foo);
 foo();
 foo();
 %OptimizeFunctionOnNextCall(foo);
 foo();
-assertEquals(0, %GetDeoptCount(foo));
+assertOptimized(foo);