Implement branching control flow in the non-optimizing graph compiler.

runtime/vm/flow_graph_compiler_x64.h

Index: runtime/vm/flow_graph_compiler_x64.h
diff --git a/runtime/vm/flow_graph_compiler_x64.h b/runtime/vm/flow_graph_compiler_x64.h
index 95127c63112272260bf5cf0692c376e55f8b37cc..6e090fff53300da1ecb09600e9268a5effc0de9b 100644
--- a/runtime/vm/flow_graph_compiler_x64.h
+++ b/runtime/vm/flow_graph_compiler_x64.h
@@ -23,12 +23,7 @@ class FlowGraphCompiler : public FlowGraphVisitor {
  public:

[srdjan, 2012/03/07 22:23:06]

Maybe write (again) that blocks are in reversed order as that they are
generated.

   FlowGraphCompiler(Assembler* assembler,
                     const ParsedFunction& parsed_function,
-                    const GrowableArray<BlockEntryInstr*>* blocks)
-      : assembler_(assembler),
-        parsed_function_(parsed_function),
-        blocks_(blocks),
-        pc_descriptors_list_(new CodeGenerator::DescriptorList()),
-        stack_local_count_(0) { }
+                    const GrowableArray<BlockEntryInstr*>* blocks);
 
   virtual ~FlowGraphCompiler() { }
 
@@ -40,12 +35,22 @@ class FlowGraphCompiler : public FlowGraphVisitor {
   void FinalizeExceptionHandlers(const Code& code);
 
  private:
+  struct BlockInfo : public ZoneAllocated {
+   public:
+    BlockInfo() : label() { }
+
+    Label label;
+  };

[srdjan, 2012/03/07 22:23:06]

ZoneAllocated objects have their destructor never called, i.e., the Label
destructor will never be called neither, i.e., the checks in Label's destructor
are not being done any longer. I think those checks are important. Maybe we
could traverse the list at the end of compilation and verify that the Labels are
OK.

[Kevin Millikin (Google), 2012/03/08 09:59:53]

I know, and I'm not certain this is best.  Label has DISALLOW_COPY_AND_ASSIGN so
it doesn't really work to use an embedded GrowableArray.

It seems possibly better to have a malloced array of BlockInfos---especially
depending on what else we put in this struct.

For now I've put the label asserts in ~FlowGraphCompiler.

+
   int stack_local_count() const { return stack_local_count_; }
   void set_stack_local_count(int count) { stack_local_count_ = count; }
+  BlockEntryInstr* current_block() const { return current_block_; }
 
   // Bail out of the flow graph compiler.  Does not return to the caller.
   void Bailout(const char* reason);
 
+  virtual void VisitBlocks(const GrowableArray<BlockEntryInstr*>& blocks);
+
   // Emit code to perform a computation, leaving its value in RAX.
 #define DECLARE_VISIT_COMPUTATION(ShortName, ClassName)                        \
   virtual void Visit##ShortName(ClassName* comp);
@@ -91,6 +96,12 @@ class FlowGraphCompiler : public FlowGraphVisitor {
   const ParsedFunction& parsed_function_;
   const GrowableArray<BlockEntryInstr*>* blocks_;
 
+  // Compiler specific per-block state.  Indexed by block number, so not
+  // necessarily the same order as the array of blocks.
+  GrowableArray<BlockInfo*> block_info_;
+
+  BlockEntryInstr* current_block_;
+
   CodeGenerator::DescriptorList* pc_descriptors_list_;
   int stack_local_count_;