Do not use recursion for depth-first traversal of straight line code.

runtime/vm/intermediate_language.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 784 matching lines @@
   Instruction() { }
 
   virtual bool IsBlockEntry() const { return false; }
   BlockEntryInstr* AsBlockEntry() {
     return IsBlockEntry() ? reinterpret_cast<BlockEntryInstr*>(this) : NULL;
   }
 
   // Visiting support.
   virtual Instruction* Accept(FlowGraphVisitor* visitor) = 0;
 
+  virtual Instruction* StraightLineSuccessor() const = 0;
   virtual void SetSuccessor(Instruction* instr) = 0;
 
   // Discover basic-block structure by performing a recursive depth first
   // traversal of the instruction graph reachable from this instruction.  As
   // a side effect, the block entry instructions in the graph are assigned
   // numbers in both preorder and postorder.  The array 'preorder' maps
   // preorder block numbers to the block entry instruction with that number
   // and analogously for the array 'postorder'.  The depth first spanning
   // tree is recorded in the array 'parent', which maps preorder block
   // numbers to the preorder number of the block's spanning-tree parent.  As
   // a side effect, the set of basic block predecessors (e.g., block entry
   // instructions of predecessor blocks) and also the last instruction in
   // the block is recorded in each entry instruction.
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent) = 0;
+      GrowableArray<BlockEntryInstr*>* parent) {
+    // Never called for instructions except block entries and branches.
+    UNREACHABLE();
+  }
 
 #define INSTRUCTION_TYPE_CHECK(type)                                           \
   virtual bool Is##type() const { return false; }                              \
   virtual type##Instr* As##type() { return NULL; }
 FOR_EACH_INSTRUCTION(INSTRUCTION_TYPE_CHECK)
 #undef INSTRUCTION_TYPE_CHECK
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Instruction);
 };
@@ skipping 33 matching lines @@
 
 class JoinEntryInstr : public BlockEntryInstr {
  public:
   JoinEntryInstr()
       : BlockEntryInstr(),
         predecessors_(2),  // Two is the assumed to be the common case.
         successor_(NULL) { }
 
   DECLARE_INSTRUCTION(JoinEntry)
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
       GrowableArray<BlockEntryInstr*>* parent);
 
  private:
   ZoneGrowableArray<BlockEntryInstr*> predecessors_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(JoinEntryInstr);
 };
 
 
 class TargetEntryInstr : public BlockEntryInstr {
  public:
   TargetEntryInstr()
       : BlockEntryInstr(), predecessor_(NULL), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(TargetEntry)
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
       GrowableArray<BlockEntryInstr*>* parent);
@@ skipping 16 matching lines @@
 class PickTempInstr : public Instruction {
  public:
   PickTempInstr(intptr_t dst, intptr_t src)
       : destination_(dst), source_(src), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(PickTemp)
 
   intptr_t destination() const { return destination_; }
   intptr_t source() const { return source_; }
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL && instr != NULL);
     successor_ = instr;
   }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   const intptr_t destination_;
   const intptr_t source_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(PickTempInstr);
 };
 
 
 // The non-optimizing compiler assumes that temporary definitions and uses
 // obey a stack discipline, so they can be allocated and deallocated with
 // push and pop.  Some Some AST nodes, e.g., expr++, violate this assumption
 // (the value expr+1 is produced after the value of expr, and also consumed
 // after it).
 //
 // We 'preallocate' temporaries (named with 'destination') such as the one
 // for expr+1 and use TuckTemp to mutate them by overwriting them with a
 // copy of a temporary (named with 'source').
 class TuckTempInstr : public Instruction {
  public:
   TuckTempInstr(intptr_t dst, intptr_t src)
       : destination_(dst), source_(src), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(TuckTemp)
 
   intptr_t destination() const { return destination_; }
   intptr_t source() const { return source_; }
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL && instr != NULL);
     successor_ = instr;
   }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   const intptr_t destination_;
   const intptr_t source_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(TuckTempInstr);
 };
 
 
 class DoInstr : public Instruction {
  public:
   explicit DoInstr(Computation* comp)
       : computation_(comp), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(Do)
 
   Computation* computation() const { return computation_; }
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   Computation* computation_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(DoInstr);
 };
 
 
 class BindInstr : public Instruction {
  public:
   BindInstr(intptr_t temp_index, Computation* computation)
       : temp_index_(temp_index), computation_(computation), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(Bind)
 
   intptr_t temp_index() const { return temp_index_; }
   Computation* computation() const { return computation_; }
 
+  virtual Instruction* StraightLineSuccessor() const {
+    return successor_;
+  }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   const intptr_t temp_index_;
   Computation* computation_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(BindInstr);
 };
 
 
 class ReturnInstr : public Instruction {
  public:
   ReturnInstr(Value* value, intptr_t token_index)
       : value_(value), token_index_(token_index) {
     ASSERT(value_ != NULL);
   }
 
   DECLARE_INSTRUCTION(Return)
 
   Value* value() const { return value_; }
   intptr_t token_index() const { return token_index_; }
 
+  virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   Value* value_;
   intptr_t token_index_;
 
   DISALLOW_COPY_AND_ASSIGN(ReturnInstr);
 };
 
 
 class ThrowInstr : public Instruction {
  public:
   ThrowInstr(intptr_t node_id, intptr_t token_index, Value* exception)
       : node_id_(node_id), token_index_(token_index), exception_(exception) {
     ASSERT(exception_ != NULL);
   }
 
   DECLARE_INSTRUCTION(Throw)
 
   intptr_t node_id() const { return node_id_; }
   intptr_t token_index() const { return token_index_; }
   Value* exception() const { return exception_; }
 
+  virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   intptr_t node_id_;
   intptr_t token_index_;
   Value* exception_;
 
   DISALLOW_COPY_AND_ASSIGN(ThrowInstr);
 };
 
 
 class ReThrowInstr : public Instruction {
@@ skipping 10 matching lines @@
     ASSERT(stack_trace_ != NULL);
   }
 
   DECLARE_INSTRUCTION(ReThrow)
 
   intptr_t node_id() const { return node_id_; }
   intptr_t token_index() const { return token_index_; }
   Value* exception() const { return exception_; }
   Value* stack_trace() const { return stack_trace_; }
 
+  virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
-  virtual void DiscoverBlocks(
-      BlockEntryInstr* current_block,
-      GrowableArray<BlockEntryInstr*>* preorder,
-      GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
-
  private:
   intptr_t node_id_;
   intptr_t token_index_;
   Value* exception_;
   Value* stack_trace_;
 
   DISALLOW_COPY_AND_ASSIGN(ReThrowInstr);
 };
 
 
 class BranchInstr : public Instruction {
  public:
   explicit BranchInstr(Value* value)
       : value_(value),
         true_successor_(NULL),
         false_successor_(NULL) { }
 
   DECLARE_INSTRUCTION(Branch)
 
   Value* value() const { return value_; }
   TargetEntryInstr* true_successor() const { return true_successor_; }
   TargetEntryInstr* false_successor() const { return false_successor_; }
 
   TargetEntryInstr** true_successor_address() { return &true_successor_; }
   TargetEntryInstr** false_successor_address() { return &false_successor_; }
 
+  virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
       GrowableArray<BlockEntryInstr*>* parent);
 
  private:
   Value* value_;
@@ skipping 43 matching lines @@
   const GrowableArray<BlockEntryInstr*>& block_order_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_