Skip loop optimization if there is no loop in the graph.

LinearizeGraph() does quite some allocations.
Also add some comments on the possible false positives of
some flags.

Test: m test-art-host
Change-Id: I80ef89a2dc031d601e7621d0b22060cd8c17fae3

1 files changed, 5 insertions, 1 deletions

diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index 95838380cc..26c9ab83c2 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -71,7 +71,7 @@ HLoopOptimization::HLoopOptimization(HGraph* graph,
 void HLoopOptimization::Run() {
   // Well-behaved loops only.
   // TODO: make this less of a sledgehammer.
-  if (graph_->HasTryCatch() || graph_->HasIrreducibleLoops()) {
+  if (!graph_->HasLoops() || graph_->HasTryCatch() || graph_->HasIrreducibleLoops()) {
     return;
   }
 
@@ -84,6 +84,10 @@ void HLoopOptimization::Run() {
   // Perform loop optimizations.
   LocalRun();
 
+  if (top_loop_ == nullptr) {
+    graph_->SetHasLoops(false);
+  }
+
   // Detach.
   loop_allocator_ = nullptr;
   last_loop_ = top_loop_ = nullptr;