[interpreter] Switch context during stack unwinding.

src/compiler/bytecode-graph-builder.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/bytecode-graph-builder.h"
 
 #include "src/compiler/bytecode-branch-analysis.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/operator-properties.h"
 #include "src/interpreter/bytecodes.h"
@@ skipping 1648 matching lines @@
     if (current_offset < current_end) break;  // Still covered by range.
     exception_handlers_.pop();
   }
 
   // Potentially enter exception handlers.
   while (current_exception_handler_ < num_entries) {
     int next_start = table->GetRangeStart(current_exception_handler_);
     if (current_offset < next_start) break;  // Not yet covered by range.
     int next_end = table->GetRangeEnd(current_exception_handler_);
     int next_handler = table->GetRangeHandler(current_exception_handler_);
-    exception_handlers_.push({next_start, next_end, next_handler});
+    int next_depth = table->GetRangeDepth(current_exception_handler_);

[Michael Starzinger, 2016/02/03 14:34:01]

disclosure: I understand that the naming of the HandlerTable::depth field is
off, because the interpreter is now "hijacking" it to hold the context register
index. However, I would like to do any potential renaming of that field in a
separate CL and not as part of this CL.

+    exception_handlers_.push({next_start, next_end, next_handler, next_depth});
     current_exception_handler_++;
   }
 }
 
 void BytecodeGraphBuilder::PrepareEntryFrameState(Node* node) {
   DCHECK_EQ(1, OperatorProperties::GetFrameStateInputCount(node->op()));
   DCHECK_EQ(IrOpcode::kDead,
             NodeProperties::GetFrameStateInput(node, 0)->opcode());
   NodeProperties::ReplaceFrameStateInput(
       node, 0, environment()->Checkpoint(BailoutId(0),
@@ skipping 46 matching lines @@
     if (NodeProperties::IsControl(result)) {
       environment()->UpdateControlDependency(result);
     }
     // Update the current effect dependency for effect-producing nodes.
     if (result->op()->EffectOutputCount() > 0) {
       environment()->UpdateEffectDependency(result);
     }
     // Add implicit exception continuation for throwing nodes.
     if (!result->op()->HasProperty(Operator::kNoThrow) && inside_handler) {
       int handler_offset = exception_handlers_.top().handler_offset_;
+      int context_index = exception_handlers_.top().context_register_;
+      interpreter::Register context_register(context_index);
       // TODO(mstarzinger): Thread through correct prediction!
       IfExceptionHint hint = IfExceptionHint::kLocallyCaught;
       Environment* success_env = environment()->CopyForConditional();
       const Operator* op = common()->IfException(hint);
       Node* effect = environment()->GetEffectDependency();
       Node* on_exception = graph()->NewNode(op, effect, result);
+      Node* context = environment()->LookupRegister(context_register);
       environment()->UpdateControlDependency(on_exception);
       environment()->UpdateEffectDependency(on_exception);
       environment()->BindAccumulator(on_exception);
+      environment()->SetContext(context);
       MergeIntoSuccessorEnvironment(handler_offset);
       set_environment(success_env);
     }
     // Add implicit success continuation for throwing nodes.
     if (!result->op()->HasProperty(Operator::kNoThrow)) {
       const Operator* if_success = common()->IfSuccess();
       Node* on_success = graph()->NewNode(if_success, result);
       environment()->UpdateControlDependency(on_success);
     }
   }
@@ skipping 73 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8