Add a type propagation phase after building SSA.

This ensures all phis have a type.

Change-Id: I7e4f9a16d1efb5f64c493c1351749b352c870cbd

4 files changed, 159 insertions, 23 deletions

diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc
index 54c3c5d..471307e 100644
--- a/compiler/optimizing/ssa_builder.cc
+++ b/compiler/optimizing/ssa_builder.cc
@@ -15,22 +15,12 @@
  */
 
 #include "ssa_builder.h"
+
 #include "nodes.h"
+#include "ssa_type_propagation.h"
 
 namespace art {
 
-static Primitive::Type MergeTypes(Primitive::Type existing, Primitive::Type new_type) {
-  // We trust the verifier has already done the necessary checking.
-  switch (existing) {
-    case Primitive::kPrimFloat:
-    case Primitive::kPrimDouble:
-    case Primitive::kPrimNot:
-      return existing;
-    default:
-      return new_type;
-  }
-}
-
 void SsaBuilder::BuildSsa() {
   // 1) Visit in reverse post order. We need to have all predecessors of a block visited
   // (with the exception of loops) in order to create the right environment for that
@@ -44,18 +34,18 @@ void SsaBuilder::BuildSsa() {
     HBasicBlock* block = loop_headers_.Get(i);
     for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) {
       HPhi* phi = it.Current()->AsPhi();
-      Primitive::Type type = Primitive::kPrimVoid;
       for (size_t pred = 0; pred < block->GetPredecessors().Size(); pred++) {
         HInstruction* input = ValueOfLocal(block->GetPredecessors().Get(pred), phi->GetRegNumber());
         phi->AddInput(input);
-        type = MergeTypes(type, input->GetType());
       }
-      phi->SetType(type);
     }
   }
-  // TODO: Now that the type of loop phis is set, we need a type propagation phase.
 
-  // 3) Clear locals.
+  // 3) Propagate types of phis.
+  SsaTypePropagation type_propagation(GetGraph());
+  type_propagation.Run();
+
+  // 4) Clear locals.
   // TODO: Move this to a dead code eliminator phase.
   for (HInstructionIterator it(GetGraph()->GetEntryBlock()->GetInstructions());
        !it.Done();
@@ -118,16 +108,10 @@ void SsaBuilder::VisitBasicBlock(HBasicBlock* block) {
       if (is_different) {
         HPhi* phi = new (GetGraph()->GetArena()) HPhi(
             GetGraph()->GetArena(), local, block->GetPredecessors().Size(), Primitive::kPrimVoid);
-        Primitive::Type type = Primitive::kPrimVoid;
         for (size_t i = 0; i < block->GetPredecessors().Size(); i++) {
           HInstruction* value = ValueOfLocal(block->GetPredecessors().Get(i), local);
-          // We need to merge the incoming types, as the Dex format does not
-          // guarantee the inputs have the same type. In particular the 0 constant is
-          // used for all types, but the graph builder treats it as an int.
-          type = MergeTypes(type, value->GetType());
           phi->SetRawInputAt(i, value);
         }
-        phi->SetType(type);
         block->AddPhi(phi);
         value = phi;
       }
diff --git a/compiler/optimizing/ssa_test.cc b/compiler/optimizing/ssa_test.cc
index 3b354f1..088a5c4 100644
--- a/compiler/optimizing/ssa_test.cc
+++ b/compiler/optimizing/ssa_test.cc
@@ -87,6 +87,13 @@ static void TestCode(const uint16_t* data, const char* expected) {
   graph->TransformToSSA();
   ReNumberInstructions(graph);
 
+  // Test that phis had their type set.
+  for (size_t i = 0, e = graph->GetBlocks().Size(); i < e; ++i) {
+    for (HInstructionIterator it(graph->GetBlocks().Get(i)->GetPhis()); !it.Done(); it.Advance()) {
+      ASSERT_NE(it.Current()->GetType(), Primitive::kPrimVoid);
+    }
+  }
+
   SsaPrettyPrinter printer(graph);
   printer.VisitInsertionOrder();
 
diff --git a/compiler/optimizing/ssa_type_propagation.cc b/compiler/optimizing/ssa_type_propagation.cc
new file mode 100644
index 0000000..53fa74e
--- /dev/null
+++ b/compiler/optimizing/ssa_type_propagation.cc
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ssa_type_propagation.h"
+
+#include "nodes.h"
+
+namespace art {
+
+static Primitive::Type MergeTypes(Primitive::Type existing, Primitive::Type new_type) {
+  // We trust the verifier has already done the necessary checking.
+  switch (existing) {
+    case Primitive::kPrimFloat:
+    case Primitive::kPrimDouble:
+    case Primitive::kPrimNot:
+      return existing;
+    default:
+      return new_type;
+  }
+}
+
+// Re-compute and update the type of the instruction. Returns
+// whether or not the type was changed.
+static bool UpdateType(HPhi* phi) {
+  Primitive::Type existing = phi->GetType();
+
+  Primitive::Type new_type = Primitive::kPrimVoid;
+  for (size_t i = 0, e = phi->InputCount(); i < e; ++i) {
+    Primitive::Type input_type = phi->InputAt(i)->GetType();
+    new_type = MergeTypes(new_type, input_type);
+  }
+  phi->SetType(new_type);
+  return existing != new_type;
+}
+
+void SsaTypePropagation::Run() {
+  for (HReversePostOrderIterator it(*graph_); !it.Done(); it.Advance()) {
+    VisitBasicBlock(it.Current());
+  }
+  ProcessWorklist();
+}
+
+void SsaTypePropagation::VisitBasicBlock(HBasicBlock* block) {
+  if (block->IsLoopHeader()) {
+    for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) {
+      HPhi* phi = it.Current()->AsPhi();
+      // Set the initial type for the phi. Use the non back edge input for reaching
+      // a fixed point faster.
+      phi->SetType(phi->InputAt(0)->GetType());
+      AddToWorklist(phi);
+    }
+  } else {
+    for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) {
+      HPhi* phi = it.Current()->AsPhi();
+      if (UpdateType(phi)) {
+        AddDependentInstructionsToWorklist(phi);
+      }
+    }
+  }
+}
+
+void SsaTypePropagation::ProcessWorklist() {
+  while (!worklist_.IsEmpty()) {
+    HPhi* instruction = worklist_.Pop();
+    if (UpdateType(instruction)) {
+      AddDependentInstructionsToWorklist(instruction);
+    }
+  }
+}
+
+void SsaTypePropagation::AddToWorklist(HPhi* instruction) {
+  worklist_.Add(instruction);
+}
+
+void SsaTypePropagation::AddDependentInstructionsToWorklist(HPhi* instruction) {
+  for (HUseIterator<HInstruction> it(instruction->GetUses()); !it.Done(); it.Advance()) {
+    HPhi* phi = it.Current()->GetUser()->AsPhi();
+    if (phi != nullptr) {
+      AddToWorklist(phi);
+    }
+  }
+}
+
+}  // namespace art
diff --git a/compiler/optimizing/ssa_type_propagation.h b/compiler/optimizing/ssa_type_propagation.h
new file mode 100644
index 0000000..5f471a9
--- /dev/null
+++ b/compiler/optimizing/ssa_type_propagation.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_COMPILER_OPTIMIZING_SSA_TYPE_PROPAGATION_H_
+#define ART_COMPILER_OPTIMIZING_SSA_TYPE_PROPAGATION_H_
+
+#include "nodes.h"
+
+namespace art {
+
+// Compute and propagate types of phis in the graph.
+class SsaTypePropagation : public ValueObject {
+ public:
+  explicit SsaTypePropagation(HGraph* graph)
+      : graph_(graph), worklist_(graph->GetArena(), kDefaultWorklistSize) {}
+
+  void Run();
+
+ private:
+  void VisitBasicBlock(HBasicBlock* block);
+  void ProcessWorklist();
+  void AddToWorklist(HPhi* phi);
+  void AddDependentInstructionsToWorklist(HPhi* phi);
+
+  HGraph* const graph_;
+  GrowableArray<HPhi*> worklist_;
+
+  static constexpr size_t kDefaultWorklistSize = 8;
+
+  DISALLOW_COPY_AND_ASSIGN(SsaTypePropagation);
+};
+
+}  // namespace art
+
+#endif  // ART_COMPILER_OPTIMIZING_SSA_TYPE_PROPAGATION_H_