[turbofan] Introduce prediction for exception handlers.

src/objects.h

 // Copyright 2012 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 5141 matching lines @@
 // the code object it is associated with. The tables comes in two flavors:
 // 1) Based on ranges: Used for unoptimized code. Contains one entry per
 //    exception handler and a range representing the try-block covered by that
 //    handler. Layout looks as follows:
 //      [ range-start , range-end , handler-offset , stack-depth ]
 // 2) Based on return addresses: Used for turbofanned code. Contains one entry
 //    per call-site that could throw an exception. Layout looks as follows:
 //      [ return-address-offset , handler-offset ]
 class HandlerTable : public FixedArray {
  public:
+  // Conservative prediction whether a given handler will locally catch an
+  // exception or cause a re-throw to outside the code boundary. Since this is
+  // undecidable it is merely an approximation (e.g. useful for debugger).
+  enum CatchPrediction { UNCAUGHT, CAUGHT };
+
   // Accessors for handler table based on ranges.
   void SetRangeStart(int index, int value) {
     set(index * kRangeEntrySize + kRangeStartIndex, Smi::FromInt(value));
   }
   void SetRangeEnd(int index, int value) {
     set(index * kRangeEntrySize + kRangeEndIndex, Smi::FromInt(value));
   }
   void SetRangeHandler(int index, int value) {
     set(index * kRangeEntrySize + kRangeHandlerIndex, Smi::FromInt(value));
   }
   void SetRangeDepth(int index, int value) {
     set(index * kRangeEntrySize + kRangeDepthIndex, Smi::FromInt(value));
   }
 
   // Accessors for handler table based on return addresses.
   void SetReturnOffset(int index, int value) {
     set(index * kReturnEntrySize + kReturnOffsetIndex, Smi::FromInt(value));
   }
-  void SetReturnHandler(int index, int value) {
+  void SetReturnHandler(int index, int offset, CatchPrediction prediction) {
+    int value = HandlerOffsetField::encode(offset) |
+                HandlerPredictionField::encode(prediction);
     set(index * kReturnEntrySize + kReturnHandlerIndex, Smi::FromInt(value));
   }
 
   // Lookup handler in a table based on ranges.
   int LookupRange(int pc_offset, int* stack_depth);
 
   // Lookup handler in a table based on return addresses.
-  int LookupReturn(int pc_offset);
+  int LookupReturn(int pc_offset, CatchPrediction* prediction);
 
   // Returns the required length of the underlying fixed array.
   static int LengthForRange(int entries) { return entries * kRangeEntrySize; }
   static int LengthForReturn(int entries) { return entries * kReturnEntrySize; }
 
   DECLARE_CAST(HandlerTable)
 
 #if defined(OBJECT_PRINT) || defined(ENABLE_DISASSEMBLER)
   void HandlerTableRangePrint(std::ostream& os);   // NOLINT
   void HandlerTableReturnPrint(std::ostream& os);  // NOLINT
 #endif
 
  private:
   // Layout description for handler table based on ranges.
   static const int kRangeStartIndex = 0;
   static const int kRangeEndIndex = 1;
   static const int kRangeHandlerIndex = 2;
   static const int kRangeDepthIndex = 3;
   static const int kRangeEntrySize = 4;
 
   // Layout description for handler table based on return addresses.
   static const int kReturnOffsetIndex = 0;
   static const int kReturnHandlerIndex = 1;
   static const int kReturnEntrySize = 2;
+
+  // Encoding of the {handler} field.
+  class HandlerPredictionField : public BitField<CatchPrediction, 0, 1> {};
+  class HandlerOffsetField : public BitField<int, 1, 30> {};
 };
 
 
 // Forward declaration.
 class Cell;
 class PropertyCell;
 class SafepointEntry;
 class TypeFeedbackInfo;
 
 // Code describes objects with on-the-fly generated machine code.
@@ skipping 5954 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_