[ignition] Only perform interrupt checks for backward jumps

Jumps (and returns) in Ignition update the interrupt budget, and call
into the runtime if the budget drops below zero. Since forward jumps
only ever increase the budget, we don't need to generate this check or
the call for them at all.

Change-Id: I8c4ae15edab39a3a5725a98f38efba3a16243d91
Reviewed-on: https://chromium-review.googlesource.com/643209Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47720}

src/interpreter/interpreter-assembler.cc

@@ -1026,7 +1026,8 @@ Node* InterpreterAssembler::CallRuntimeN(Node* function_id, Node* context,
 }
 
 void InterpreterAssembler::UpdateInterruptBudget(Node* weight, bool backward) {
-  Label ok(this), interrupt_check(this, Label::kDeferred), end(this);
+  Comment("[ UpdateInterruptBudget");
+
   Node* budget_offset =
       IntPtrConstant(BytecodeArray::kInterruptBudgetOffset - kHeapObjectTag);
 
@@ -1041,28 +1042,35 @@ void InterpreterAssembler::UpdateInterruptBudget(Node* weight, bool backward) {
   // Make sure we include the current bytecode in the budget calculation.
   Node* budget_after_bytecode =
       Int32Sub(old_budget, Int32Constant(CurrentBytecodeSize()));
+
   if (backward) {
     new_budget.Bind(Int32Sub(budget_after_bytecode, weight));
+
+    Node* condition =
+        Int32GreaterThanOrEqual(new_budget.value(), Int32Constant(0));
+    Label ok(this), interrupt_check(this, Label::kDeferred);
+    Branch(condition, &ok, &interrupt_check);
+
+    // Perform interrupt and reset budget.
+    BIND(&interrupt_check);
+    {
+      CallRuntime(Runtime::kInterrupt, GetContext());
+      new_budget.Bind(Int32Constant(Interpreter::InterruptBudget()));
+      Goto(&ok);
+    }
+
+    BIND(&ok);
   } else {
+    // For a forward jump, we know we only increase the interrupt budget, so
+    // no need to check if it's below zero.
     new_budget.Bind(Int32Add(budget_after_bytecode, weight));
   }
-  Node* condition =
-      Int32GreaterThanOrEqual(new_budget.value(), Int32Constant(0));
-  Branch(condition, &ok, &interrupt_check);
-
-  // Perform interrupt and reset budget.
-  BIND(&interrupt_check);
-  {
-    CallRuntime(Runtime::kInterrupt, GetContext());
-    new_budget.Bind(Int32Constant(Interpreter::InterruptBudget()));
-    Goto(&ok);
-  }
 
   // Update budget.
-  BIND(&ok);
   StoreNoWriteBarrier(MachineRepresentation::kWord32,
                       BytecodeArrayTaggedPointer(), budget_offset,
                       new_budget.value());
+  Comment("] UpdateInterruptBudget");
 }
 
 Node* InterpreterAssembler::Advance() { return Advance(CurrentBytecodeSize()); }