Fix a bug in block reordering/block compaction.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index ec9c31bc1160aaf824df97261e97002f712aa52d..96a17b0dacc8530c2bffa9fac67338920abc8db1 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -4530,6 +4530,13 @@ void ReThrowInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 }
 
 
+void GraphEntryInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  if (!compiler->CanFallThroughTo(normal_entry())) {
+    __ jmp(compiler->GetJumpLabel(normal_entry()));
+  }
+}
+
+
 void TargetEntryInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ Bind(compiler->GetJumpLabel(this));
   if (!compiler->is_optimizing()) {
@@ -4605,11 +4612,10 @@ void ControlInstruction::EmitBranchOnValue(FlowGraphCompiler* compiler,
 void ControlInstruction::EmitBranchOnCondition(FlowGraphCompiler* compiler,
                                                Condition true_condition) {
   if (compiler->CanFallThroughTo(false_successor())) {
-    // If the next block is the false successor we will fall through to it.
+    // If the next block is the false successor, fall through to it.
     __ j(true_condition, compiler->GetJumpLabel(true_successor()));
   } else {
-    // If the next block is the true successor we negate comparison and fall
-    // through to it.
+    // If the next block is not the false successor, branch to it.
     Condition false_condition = NegateCondition(true_condition);
     __ j(false_condition, compiler->GetJumpLabel(false_successor()));