Fix performance regression.

Rationale:
One "improvement" overlooked in the previous CL hoists
a try-test out of the optimization to make sure we don't
change HIR when not needed. However, the try-test may
affect the outcome of the test, so that was bad, bad!

Bug: 64091002
Test: test-art-host
Change-Id: Icf5f73e7cbeb209ee5fa5f6c1bef64fe127bb2fd

1 files changed, 10 insertions, 5 deletions

diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index 4143462c71..027ba7741c 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -490,13 +490,18 @@ void HLoopOptimization::SimplifyInduction(LoopNode* node) {
   for (HInstructionIterator it(header->GetPhis()); !it.Done(); it.Advance()) {
     HPhi* phi = it.Current()->AsPhi();
     if (TrySetPhiInduction(phi, /*restrict_uses*/ true) &&
-        CanRemoveCycle() &&
         TryAssignLastValue(node->loop_info, phi, preheader, /*collect_loop_uses*/ false)) {
-      simplified_ = true;
-      for (HInstruction* i : *iset_) {
-        RemoveFromCycle(i);
+      // Note that it's ok to have replaced uses after the loop with the last value, without
+      // being able to remove the cycle. Environment uses (which are the reason we may not be
+      // able to remove the cycle) within the loop will still hold the right value. We must
+      // have tried first, however, to replace outside uses.
+      if (CanRemoveCycle()) {
+        simplified_ = true;
+        for (HInstruction* i : *iset_) {
+          RemoveFromCycle(i);
+        }
+        DCHECK(CheckInductionSetFullyRemoved(iset_));
       }
-      DCHECK(CheckInductionSetFullyRemoved(iset_));
     }
   }
 }