Introduce Goto instructions to the flow graph.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 01995ad894732b73fa1f5bc323c7746fa0c6ddfd..7bc041f49631688820bd3b97499a21ba32ae2d9d 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -1682,14 +1682,15 @@ FOR_EACH_COMPUTATION(DEFINE_PREDICATE)
   M(GraphEntry)                                                                \
   M(JoinEntry)                                                                 \
   M(TargetEntry)                                                               \
-  M(Bind)                                                                      \
   M(Phi)                                                                       \
+  M(Bind)                                                                      \
+  M(Parameter)                                                                 \
+  M(ParallelMove)                                                              \
   M(Return)                                                                    \
   M(Throw)                                                                     \
   M(ReThrow)                                                                   \
+  M(Goto)                                                                      \
   M(Branch)                                                                    \
-  M(ParallelMove)                                                              \
-  M(Parameter)
 
 
 // Forward declarations for Instruction classes.
@@ -1761,6 +1762,7 @@ class Instruction : public ZoneAllocated {
     ASSERT(!IsReturn());
     ASSERT(!IsBranch());
     ASSERT(!IsPhi());
+    ASSERT(instr == NULL || !instr->IsBlockEntry());
     // TODO(fschneider): Also add Throw and ReThrow to the list of instructions

[srdjan, 2012/07/12 16:42:26]

parenthesis

     // that do not have a successor. Currently, the graph builder will continue
     // to append instruction in case of a Throw inside an expression. This
@@ -1774,6 +1776,8 @@ class Instruction : public ZoneAllocated {
   virtual intptr_t SuccessorCount() const;
   virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
 
+  void Goto(JoinEntryInstr* entry);
+
   // 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
@@ -1852,8 +1856,7 @@ FOR_EACH_INSTRUCTION(INSTRUCTION_TYPE_CHECK)
 
 class InstructionWithInputs : public Instruction {
  public:
-  InstructionWithInputs() : locs_(NULL) {
-  }
+  InstructionWithInputs() : locs_(NULL) { }
 
   virtual LocationSummary* locs() {
     if (locs_ == NULL) {
@@ -2286,6 +2289,26 @@ class ReThrowInstr : public InstructionWithInputs {
 };
 
 
+class GotoInstr : public InstructionWithInputs {

[srdjan, 2012/07/12 16:42:26]

Why is a goto InstructionWithInputs and not just Instruction? Please add
comment.

[Kevin Millikin (Google), 2012/07/13 15:34:59]

Well, it's an instruction with inputs that happens to have zero of them :)

InstructionWithInputs seems like the wrong name or else the wrong abstraction. 
There's a handful of virtual functions related to the register allocator and
code generator (already, and there will probably become more) that assume that
they will only be called on InstructionWithInputs.  

*Avoiding* to call them requires checking the instruction type in the driver
loop (with a virtual method) rather than just making the virtual method safe to
call in the first place.

I'll add a comment, but it still needs more some cleanup.

+ public:
+  explicit GotoInstr(JoinEntryInstr* entry) : successor_(entry) { }
+
+  DECLARE_INSTRUCTION(Goto)
+
+  JoinEntryInstr* successor() const { return successor_; }
+  void set_successor(JoinEntryInstr* successor) { successor_ = successor; }
+  virtual intptr_t SuccessorCount() const;
+  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
+
+  virtual LocationSummary* MakeLocationSummary() const;
+
+  virtual void EmitNativeCode(FlowGraphCompiler* compiler);
+
+ private:
+  JoinEntryInstr* successor_;

[srdjan, 2012/07/12 16:42:26]

DISALLOW_...

+};
+
+
 class BranchInstr : public InstructionWithInputs {
  public:
   explicit BranchInstr(Value* value)