[turbofan] Introduce CheckPoint common operator.

This operator will be used to carry eager frame states, and is hooked up
to the effect chain with a control dependency to avoid hosting out of
control structures.

R=jarin@chromium.org
BUG=v8:5021

Review-Url: https://codereview.chromium.org/1993593002
Cr-Commit-Position: refs/heads/master@{#36301}

src/compiler/common-operator.cc

@@ -179,6 +179,7 @@ std::ostream& operator<<(std::ostream& os,
   V(Terminate, Operator::kKontrol, 0, 1, 1, 0, 0, 1)         \
   V(OsrNormalEntry, Operator::kFoldable, 0, 1, 1, 0, 1, 1)   \
   V(OsrLoopEntry, Operator::kFoldable, 0, 1, 1, 0, 1, 1)     \
+  V(CheckPoint, Operator::kKontrol, 1, 1, 1, 0, 1, 0)        \
   V(BeginRegion, Operator::kNoThrow, 0, 1, 0, 0, 1, 0)       \
   V(FinishRegion, Operator::kNoThrow, 1, 1, 0, 1, 1, 0)
 

src/compiler/common-operator.h

@@ -190,6 +190,7 @@ class CommonOperatorBuilder final : public ZoneObject {
   const Operator* Phi(MachineRepresentation representation,
                       int value_input_count);
   const Operator* EffectPhi(int effect_input_count);
+  const Operator* CheckPoint();
   const Operator* Guard(Type* type);
   const Operator* BeginRegion();
   const Operator* FinishRegion();

src/compiler/effect-control-linearizer.cc

@@ -293,6 +293,15 @@ void EffectControlLinearizer::ProcessNode(Node* node, Node** effect,
     return RemoveRegionNode(node);
   }
 
+  // Special treatment for CheckPoint nodes.
+  // TODO(epertoso): Pickup the current frame state.
+  if (node->opcode() == IrOpcode::kCheckPoint) {
+    // Unlink the check point; effect uses will be updated to the incoming
+    // effect that is passed.
+    node->Kill();
+    return;
+  }
+
   if (node->opcode() == IrOpcode::kIfSuccess) {
     // We always schedule IfSuccess with its call, so skip it here.
     DCHECK_EQ(IrOpcode::kCall, node->InputAt(0)->opcode());

src/compiler/opcodes.h

@@ -47,6 +47,7 @@
   V(Select)              \
   V(Phi)                 \
   V(EffectPhi)           \
+  V(CheckPoint)          \
   V(Guard)               \
   V(BeginRegion)         \
   V(FinishRegion)        \

src/compiler/typer.cc

@@ -706,6 +706,10 @@ Type* Typer::Visitor::TypeGuard(Node* node) {
   return Type::Intersect(input_type, guard_type, zone());
 }
 
+Type* Typer::Visitor::TypeCheckPoint(Node* node) {
+  UNREACHABLE();
+  return nullptr;
+}
 
 Type* Typer::Visitor::TypeBeginRegion(Node* node) {
   UNREACHABLE();

src/compiler/verifier.cc

@@ -420,6 +420,10 @@ void Verifier::Visitor::Check(Node* node) {
     case IrOpcode::kGuard:
       // TODO(bmeurer): what are the constraints on these?
       break;
+    case IrOpcode::kCheckPoint:
+      // Type is empty.
+      CheckNotTyped(node);
+      break;
     case IrOpcode::kBeginRegion:
       // TODO(rossberg): what are the constraints on these?
       break;