ART: Refactor SsaBuilder for more precise typing info

This patch refactors the SsaBuilder to do the following:

1) All phis are constructed live and marked dead if not used or proved
to be conflicting.

2) Primitive type propagation, now not a separate pass, identifies
conflicting types and marks corresponding phis dead.

3) When compiling --debuggable, DeadPhiHandling used to revive phis
which had only environmental uses but did not attempt to resolve
conflicts. This pass was removed as obsolete and is now superseded
by primitive type propagation (identifying conflicting phis) and
SsaDeadPhiEliminiation (keeping phis live if debuggable + env use).

4) Resolving conflicts requires correct primitive type information
on all instructions. This was not the case for ArrayGet instructions
which can have ambiguous types in the bytecode. To this end,
SsaBuilder now runs reference type propagation and types ArrayGets
from the type of the input array.

5) With RTP being run inside the SsaBuilder, it is not necessary to
run it as a separate optimization pass. Optimizations can now assume
that all instructions of type kPrimNot have reference type info after
SsaBuilder (with the exception of NullConstant).

6) Graph now contains a reference type to be assigned to NullConstant.
All reference type instructions therefore have RTI, as now enforced
by the SsaChecker.

Bug: 24252151
Bug: 24252100
Bug: 22538329
Bug: 25786318

Change-Id: I7a3aee1ff66c82d64b4846611c547af17e91d260

1 files changed, 41 insertions, 8 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 926bc156cf..bb0b545c1e 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -198,10 +198,38 @@ void HGraph::ComputeDominanceInformation() {
   }
 }
 
-void HGraph::TransformToSsa() {
-  DCHECK(!reverse_post_order_.empty());
-  SsaBuilder ssa_builder(this);
-  ssa_builder.BuildSsa();
+BuildSsaResult HGraph::TryBuildingSsa(StackHandleScopeCollection* handles) {
+  BuildDominatorTree();
+
+  // The SSA builder requires loops to all be natural. Specifically, the dead phi
+  // elimination phase checks the consistency of the graph when doing a post-order
+  // visit for eliminating dead phis: a dead phi can only have loop header phi
+  // users remaining when being visited.
+  BuildSsaResult result = AnalyzeNaturalLoops();
+  if (result != kBuildSsaSuccess) {
+    return result;
+  }
+
+  // Precompute per-block try membership before entering the SSA builder,
+  // which needs the information to build catch block phis from values of
+  // locals at throwing instructions inside try blocks.
+  ComputeTryBlockInformation();
+
+  // Create the inexact Object reference type and store it in the HGraph.
+  ScopedObjectAccess soa(Thread::Current());
+  ClassLinker* linker = Runtime::Current()->GetClassLinker();
+  inexact_object_rti_ = ReferenceTypeInfo::Create(
+      handles->NewHandle(linker->GetClassRoot(ClassLinker::kJavaLangObject)),
+      /* is_exact */ false);
+
+  // Tranforms graph to SSA form.
+  result = SsaBuilder(this, handles).BuildSsa();
+  if (result != kBuildSsaSuccess) {
+    return result;
+  }
+
+  in_ssa_form_ = true;
+  return kBuildSsaSuccess;
 }
 
 HBasicBlock* HGraph::SplitEdge(HBasicBlock* block, HBasicBlock* successor) {
@@ -410,7 +438,7 @@ void HGraph::SimplifyCFG() {
   }
 }
 
-bool HGraph::AnalyzeNaturalLoops() const {
+BuildSsaResult HGraph::AnalyzeNaturalLoops() const {
   // Order does not matter.
   for (HReversePostOrderIterator it(*this); !it.Done(); it.Advance()) {
     HBasicBlock* block = it.Current();
@@ -418,16 +446,16 @@ bool HGraph::AnalyzeNaturalLoops() const {
       if (block->IsCatchBlock()) {
         // TODO: Dealing with exceptional back edges could be tricky because
         //       they only approximate the real control flow. Bail out for now.
-        return false;
+        return kBuildSsaFailThrowCatchLoop;
       }
       HLoopInformation* info = block->GetLoopInformation();
       if (!info->Populate()) {
         // Abort if the loop is non natural. We currently bailout in such cases.
-        return false;
+        return kBuildSsaFailNonNaturalLoop;
       }
     }
   }
-  return true;
+  return kBuildSsaSuccess;
 }
 
 void HGraph::InsertConstant(HConstant* constant) {
@@ -446,8 +474,13 @@ HNullConstant* HGraph::GetNullConstant(uint32_t dex_pc) {
   // id and/or any invariants the graph is assuming when adding new instructions.
   if ((cached_null_constant_ == nullptr) || (cached_null_constant_->GetBlock() == nullptr)) {
     cached_null_constant_ = new (arena_) HNullConstant(dex_pc);
+    cached_null_constant_->SetReferenceTypeInfo(inexact_object_rti_);
     InsertConstant(cached_null_constant_);
   }
+  if (kIsDebugBuild) {
+    ScopedObjectAccess soa(Thread::Current());
+    DCHECK(cached_null_constant_->GetReferenceTypeInfo().IsValid());
+  }
   return cached_null_constant_;
 }