ART: Rediscover loops after deleting blocks in DCE

The way DCE currently updates loop information does not cover all
cases. This patch removes the logic, resets loop information of live
blocks to pre-SSA state and reanalyzes the affected loops.

Change-Id: I0b996a70235b95a8db0de9a23a03f71db57a21b8
(cherry picked from commit a4b8c21dae70ae34aee13628632c39a675c06022)

1 files changed, 35 insertions, 14 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index b9e58c7032..41adc7223e 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -17,6 +17,7 @@
 #include "nodes.h"
 
 #include "ssa_builder.h"
+#include "base/bit_vector-inl.h"
 #include "utils/growable_array.h"
 #include "scoped_thread_state_change.h"
 
@@ -346,6 +347,7 @@ void HLoopInformation::PopulateRecursive(HBasicBlock* block) {
 }
 
 bool HLoopInformation::Populate() {
+  DCHECK_EQ(blocks_.NumSetBits(), 0u) << "Loop information has already been populated";
   for (size_t i = 0, e = GetBackEdges().Size(); i < e; ++i) {
     HBasicBlock* back_edge = GetBackEdges().Get(i);
     DCHECK(back_edge->GetDominator() != nullptr);
@@ -365,6 +367,39 @@ bool HLoopInformation::Populate() {
   return true;
 }
 
+void HLoopInformation::Update() {
+  HGraph* graph = header_->GetGraph();
+  for (uint32_t id : blocks_.Indexes()) {
+    HBasicBlock* block = graph->GetBlocks().Get(id);
+    // Reset loop information of non-header blocks inside the loop, except
+    // members of inner nested loops because those should already have been
+    // updated by their own LoopInformation.
+    if (block->GetLoopInformation() == this && block != header_) {
+      block->SetLoopInformation(nullptr);
+    }
+  }
+  blocks_.ClearAllBits();
+
+  if (back_edges_.IsEmpty()) {
+    // The loop has been dismantled, delete its suspend check and remove info
+    // from the header.
+    DCHECK(HasSuspendCheck());
+    header_->RemoveInstruction(suspend_check_);
+    header_->SetLoopInformation(nullptr);
+    header_ = nullptr;
+    suspend_check_ = nullptr;
+  } else {
+    if (kIsDebugBuild) {
+      for (size_t i = 0, e = back_edges_.Size(); i < e; ++i) {
+        DCHECK(header_->Dominates(back_edges_.Get(i)));
+      }
+    }
+    // This loop still has reachable back edges. Repopulate the list of blocks.
+    bool populate_successful = Populate();
+    DCHECK(populate_successful);
+  }
+}
+
 HBasicBlock* HLoopInformation::GetPreHeader() const {
   return header_->GetDominator();
 }
@@ -1049,20 +1084,6 @@ void HBasicBlock::DisconnectAndDelete() {
   SetGraph(nullptr);
 }
 
-void HBasicBlock::UpdateLoopInformation() {
-  // Check if loop information points to a dismantled loop. If so, replace with
-  // the loop information of a larger loop which contains this block, or nullptr
-  // otherwise. We iterate in case the larger loop has been destroyed too.
-  while (IsInLoop() && loop_information_->GetBackEdges().IsEmpty()) {
-    if (IsLoopHeader()) {
-      HSuspendCheck* suspend_check = loop_information_->GetSuspendCheck();
-      DCHECK_EQ(suspend_check->GetBlock(), this);
-      RemoveInstruction(suspend_check);
-    }
-    loop_information_ = loop_information_->GetPreHeader()->GetLoopInformation();
-  }
-}
-
 void HBasicBlock::MergeWith(HBasicBlock* other) {
   DCHECK_EQ(GetGraph(), other->GetGraph());
   DCHECK(GetDominatedBlocks().Contains(other));