Quick: Avoid unnecessary GVN work in release builds.

In GVN's post-processing phase, compare LVNs only in debug
builds as they should be equal anyway.

Remove the Gate() from GVN cleanup pass and remove the
DCHECK() from MIRGraph::GlobalValueNumberingCleanup()
to make it a no-op if the GVN didn't run.

Bug: 16398693
Change-Id: Ia4f1e7e3ecf12d0305966c86e0e7dbae61dab0b7

4 files changed, 6 insertions, 16 deletions

diff --git a/compiler/dex/bb_optimizations.cc b/compiler/dex/bb_optimizations.cc
index f351d990d0..11a7e44f98 100644
--- a/compiler/dex/bb_optimizations.cc
+++ b/compiler/dex/bb_optimizations.cc
@@ -17,7 +17,6 @@
 #include "bb_optimizations.h"
 #include "dataflow_iterator.h"
 #include "dataflow_iterator-inl.h"
-#include "global_value_numbering.h"
 
 namespace art {
 
@@ -80,14 +79,4 @@ bool MethodUseCount::Worker(PassDataHolder* data) const {
   return false;
 }
 
-bool GlobalValueNumberingCleanupPass::Gate(const PassDataHolder* data) const {
-  DCHECK(data != nullptr);
-  CompilationUnit* c_unit = down_cast<const PassMEDataHolder*>(data)->c_unit;
-  DCHECK(c_unit != nullptr);
-  // Do not do cleanup if GVN skipped this.
-  // TODO: Proper dependencies between passes?
-  return !GlobalValueNumbering::Skip(c_unit);
-}
-
-
 }  // namespace art
diff --git a/compiler/dex/bb_optimizations.h b/compiler/dex/bb_optimizations.h
index b948afd605..eb87c29f9d 100644
--- a/compiler/dex/bb_optimizations.h
+++ b/compiler/dex/bb_optimizations.h
@@ -284,9 +284,6 @@ class GlobalValueNumberingCleanupPass : public PassME {
     : PassME("GVNCleanup", kNoNodes, "") {
   }
 
-  // Depends on GlobalValueNumbering, so implemented in cc file.
-  bool Gate(const PassDataHolder* data) const OVERRIDE;
-
   void Start(PassDataHolder* data) const OVERRIDE {
     DCHECK(data != nullptr);
     CompilationUnit* c_unit = down_cast<const PassMEDataHolder*>(data)->c_unit;
diff --git a/compiler/dex/global_value_numbering.cc b/compiler/dex/global_value_numbering.cc
index 30e3ce0354..e2b99871c8 100644
--- a/compiler/dex/global_value_numbering.cc
+++ b/compiler/dex/global_value_numbering.cc
@@ -128,8 +128,9 @@ bool GlobalValueNumbering::FinishBasicBlock(BasicBlock* bb) {
   ++bbs_processed_;
   merge_lvns_.clear();
 
-  bool change = (lvns_[bb->id] == nullptr) || !lvns_[bb->id]->Equals(*work_lvn_);
+  bool change = false;
   if (mode_ == kModeGvn) {
+    change = (lvns_[bb->id] == nullptr) || !lvns_[bb->id]->Equals(*work_lvn_);
     // In GVN mode, keep the latest LVN even if Equals() indicates no change. This is
     // to keep the correct values of fields that do not contribute to Equals() as long
     // as they depend only on predecessor LVNs' fields that do contribute to Equals().
@@ -137,6 +138,9 @@ bool GlobalValueNumbering::FinishBasicBlock(BasicBlock* bb) {
     std::unique_ptr<const LocalValueNumbering> old_lvn(lvns_[bb->id]);
     lvns_[bb->id] = work_lvn_.release();
   } else {
+    DCHECK_EQ(mode_, kModeGvnPostProcessing);  // kModeLvn doesn't use FinishBasicBlock().
+    DCHECK(lvns_[bb->id] != nullptr);
+    DCHECK(lvns_[bb->id]->Equals(*work_lvn_));
     work_lvn_.reset();
   }
   return change;
diff --git a/compiler/dex/mir_optimization.cc b/compiler/dex/mir_optimization.cc
index 3482602704..f7107c159d 100644
--- a/compiler/dex/mir_optimization.cc
+++ b/compiler/dex/mir_optimization.cc
@@ -1451,13 +1451,13 @@ void MIRGraph::EliminateDeadCodeEnd() {
 }
 
 void MIRGraph::GlobalValueNumberingCleanup() {
+  // If the GVN didn't run, these pointers should be null and everything is effectively no-op.
   delete temp_.gvn.dce;
   temp_.gvn.dce = nullptr;
   delete temp_.gvn.gvn;
   temp_.gvn.gvn = nullptr;
   temp_.gvn.ifield_ids = nullptr;
   temp_.gvn.sfield_ids = nullptr;
-  DCHECK(temp_scoped_alloc_ != nullptr);
   temp_scoped_alloc_.reset();
 }