Ignore redundant parallel moves when checking if a block is empty.

Single predecessor blocks containing nothing but redundant parallel moves can be compacted away.

R=zerny@google.com
BUG=http://dartbug.com/21302

Review URL: https://codereview.chromium.org//669613003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@41187 260f80e4-7a28-3924-810f-c04153c831b5

runtime/vm/flow_graph_compiler.cc

@@ -225,9 +225,9 @@ bool FlowGraphCompiler::ForceSlowPathForStackOverflow() const {
 
 
 static bool IsEmptyBlock(BlockEntryInstr* block) {
-  return !block->HasParallelMove() &&
+  return !block->HasNonRedundantParallelMove() &&
          block->next()->IsGoto() &&
-         !block->next()->AsGoto()->HasParallelMove();
+         !block->next()->AsGoto()->HasNonRedundantParallelMove();
 }
 
 

runtime/vm/intermediate_language.cc

@@ -2566,6 +2566,16 @@ void ParameterInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 }
 
 
+bool ParallelMoveInstr::IsRedundant() const {
+  for (intptr_t i = 0; i < moves_.length(); i++) {
+    if (!moves_[i]->IsRedundant()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
 LocationSummary* ParallelMoveInstr::MakeLocationSummary(Isolate* isolate,
                                                         bool optimizing) const {
   return NULL;

runtime/vm/intermediate_language.h

@@ -1078,6 +1078,8 @@ class ParallelMoveInstr : public TemplateInstruction<0> {
 
   intptr_t NumMoves() const { return moves_.length(); }
 
+  bool IsRedundant() const;
+
   virtual void PrintTo(BufferFormatter* f) const;
 
   virtual bool MayThrow() const { return false; }
@@ -1138,6 +1140,10 @@ class BlockEntryInstr : public Instruction {
     return parallel_move_ != NULL;
   }
 
+  bool HasNonRedundantParallelMove() const {
+    return HasParallelMove() && !parallel_move()->IsRedundant();
+  }
+
   ParallelMoveInstr* GetParallelMove() {
     if (parallel_move_ == NULL) {
       parallel_move_ = new ParallelMoveInstr();
@@ -2167,6 +2173,10 @@ class GotoInstr : public TemplateInstruction<0> {
     return parallel_move_ != NULL;
   }
 
+  bool HasNonRedundantParallelMove() const {
+    return HasParallelMove() && !parallel_move()->IsRedundant();
+  }
+
   ParallelMoveInstr* GetParallelMove() {
     if (parallel_move_ == NULL) {
       parallel_move_ = new ParallelMoveInstr();