Fix another case of live_in at irreducible loop entry.

GVN was implicitly extending the liveness of an instruction across
an irreducible loop.

Fix this problem by clearing the value set at loop entries that contain
an irreducible loop.

bug:28252896
Change-Id: I68823cb88dceb4c2b4545286ba54fd0c958a48b0

1 files changed, 13 insertions, 2 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index eb9c381c4e..3910ca402a 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -442,8 +442,10 @@ void HGraph::SimplifyCFG() {
 }
 
 GraphAnalysisResult HGraph::AnalyzeLoops() const {
-  // Order does not matter.
-  for (HReversePostOrderIterator it(*this); !it.Done(); it.Advance()) {
+  // We iterate post order to ensure we visit inner loops before outer loops.
+  // `PopulateRecursive` needs this guarantee to know whether a natural loop
+  // contains an irreducible loop.
+  for (HPostOrderIterator it(*this); !it.Done(); it.Advance()) {
     HBasicBlock* block = it.Current();
     if (block->IsLoopHeader()) {
       if (block->IsCatchBlock()) {
@@ -576,6 +578,14 @@ void HLoopInformation::PopulateRecursive(HBasicBlock* block) {
 
   blocks_.SetBit(block->GetBlockId());
   block->SetInLoop(this);
+  if (block->IsLoopHeader()) {
+    // We're visiting loops in post-order, so inner loops must have been
+    // populated already.
+    DCHECK(block->GetLoopInformation()->IsPopulated());
+    if (block->GetLoopInformation()->IsIrreducible()) {
+      contains_irreducible_loop_ = true;
+    }
+  }
   for (HBasicBlock* predecessor : block->GetPredecessors()) {
     PopulateRecursive(predecessor);
   }
@@ -679,6 +689,7 @@ void HLoopInformation::Populate() {
   }
   if (is_irreducible_loop) {
     irreducible_ = true;
+    contains_irreducible_loop_ = true;
     graph->SetHasIrreducibleLoops(true);
   }
 }