[turbofan] Disable inline allocation of closures.

This puts lowering of {JSCreateClosure} operations behind a flag. For
now the benefit of inline allocating such closures is negligible, it
does increase code size, and breaks in combination with inlining based
on {SharedFunctionInfo}.

R=jarin@chromium.org
BUG=v8:2206

Review-Url: https://codereview.chromium.org/2636493002
Cr-Commit-Position: refs/heads/master@{#42331}

src/compiler/js-create-lowering.cc

@@ -751,6 +751,7 @@ Reduction JSCreateLowering::ReduceJSCreateArray(Node* node) {
 }
 
 Reduction JSCreateLowering::ReduceJSCreateClosure(Node* node) {
+  if (!FLAG_turbo_lower_create_closure) return NoChange();
   DCHECK_EQ(IrOpcode::kJSCreateClosure, node->opcode());
   CreateClosureParameters const& p = CreateClosureParametersOf(node->op());
   Handle<SharedFunctionInfo> shared = p.shared_info();

src/flag-definitions.h

@@ -486,6 +486,8 @@ DEFINE_BOOL(turbo_stress_instruction_scheduling, false,
             "randomly schedule instructions to stress dependency tracking")
 DEFINE_BOOL(turbo_store_elimination, true,
             "enable store-store elimination in TurboFan")
+DEFINE_BOOL(turbo_lower_create_closure, false,
+            "enable inline allocation for closure instantiation")
 
 // Flags to help platform porters
 DEFINE_BOOL(minimal, false,

test/unittests/compiler/js-create-lowering-unittest.cc

@@ -140,6 +140,7 @@ TEST_F(JSCreateLoweringTest, JSCreateArgumentsInlinedRestArray) {
 // JSCreateClosure
 
 TEST_F(JSCreateLoweringTest, JSCreateClosureViaInlinedAllocation) {
+  if (!FLAG_turbo_lower_create_closure) return;
   Node* const context = UndefinedConstant();
   Node* const effect = graph()->start();
   Node* const control = graph()->start();