[TurboFan] Provide a DebugBreak() operation to the graph assembler.

Now that we are writing more complex code in the effect control
linearizer, it can be helpful to stop in certain cases during
development / debugging.

Bug: 
Change-Id: Ibeafe807c43e092534509d4d9c3f84f9c20525a5
Reviewed-on: https://chromium-review.googlesource.com/584749Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46869}

src/compiler/graph-assembler.cc

@@ -130,6 +130,11 @@ Node* GraphAssembler::StoreElement(ElementAccess const& access, Node* object,
                               value, current_effect_, current_control_);
 }
 
+Node* GraphAssembler::DebugBreak() {
+  return current_effect_ = graph()->NewNode(machine()->DebugBreak(),
+                                            current_effect_, current_control_);
+}
+
 Node* GraphAssembler::Store(StoreRepresentation rep, Node* object, Node* offset,
                             Node* value) {
   return current_effect_ =

src/compiler/graph-assembler.h

@@ -260,6 +260,9 @@ class GraphAssembler {
   CHECKED_ASSEMBLER_MACH_BINOP_LIST(BINOP_DECL)
 #undef BINOP_DECL
 
+  // Debugging
+  Node* DebugBreak();
+
   Node* Float64RoundDown(Node* value);
 
   Node* ToNumber(Node* value);

src/compiler/machine-operator.cc

@@ -651,7 +651,7 @@ struct MachineOperatorGlobalCache {
   struct DebugBreakOperator : public Operator {
     DebugBreakOperator()
         : Operator(IrOpcode::kDebugBreak, Operator::kNoThrow, "DebugBreak", 0,
-                   0, 0, 0, 0, 0) {}
+                   1, 1, 0, 1, 0) {}
   };
   DebugBreakOperator kDebugBreak;
 

src/compiler/memory-optimizer.cc

@@ -97,6 +97,7 @@ void MemoryOptimizer::VisitNode(Node* node, AllocationState const* state) {
     case IrOpcode::kProtectedStore:
     case IrOpcode::kRetain:
     case IrOpcode::kUnsafePointerAdd:
+    case IrOpcode::kDebugBreak:
       return VisitOtherEffect(node, state);
     default:
       break;