A first implementation of a loop optimization framework.

Rationale:
We are planning to add more and more loop related optimizations
and this framework provides the basis to do so. For starters,
the framework optimizes dead induction, induction that can be
replaced with a simpler closed-form, and eliminates dead loops
completely (either pre-existing or as a result of induction
removal).

Speedup on e.g. Benchpress Loop is 73x (17.5us. -> 0.24us.)
[with the potential for more exploiting outer loop too]

Test: 618-checker-induction et al.

Change-Id: If80a809acf943539bf6726b0030dcabd50c9babc

1 files changed, 193 insertions, 0 deletions

diff --git a/compiler/optimizing/loop_optimization_test.cc b/compiler/optimizing/loop_optimization_test.cc
new file mode 100644
index 0000000000..4e007d4e9a
--- /dev/null
+++ b/compiler/optimizing/loop_optimization_test.cc
@@ -0,0 +1,193 @@
+/*
+ * Copyright (C) 2016 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 "loop_optimization.h"
+#include "optimizing_unit_test.h"
+
+namespace art {
+
+/**
+ * Fixture class for the loop optimization tests. These unit tests focus
+ * constructing the loop hierarchy. Actual optimizations are tested
+ * through the checker tests.
+ */
+class LoopOptimizationTest : public CommonCompilerTest {
+ public:
+  LoopOptimizationTest()
+      : pool_(),
+        allocator_(&pool_),
+        graph_(CreateGraph(&allocator_)),
+        iva_(new (&allocator_) HInductionVarAnalysis(graph_)),
+        loop_opt_(new (&allocator_) HLoopOptimization(graph_, iva_)) {
+    BuildGraph();
+  }
+
+  ~LoopOptimizationTest() { }
+
+  /** Constructs bare minimum graph. */
+  void BuildGraph() {
+    graph_->SetNumberOfVRegs(1);
+    entry_block_ = new (&allocator_) HBasicBlock(graph_);
+    return_block_ = new (&allocator_) HBasicBlock(graph_);
+    exit_block_ = new (&allocator_) HBasicBlock(graph_);
+    graph_->AddBlock(entry_block_);
+    graph_->AddBlock(return_block_);
+    graph_->AddBlock(exit_block_);
+    graph_->SetEntryBlock(entry_block_);
+    graph_->SetExitBlock(exit_block_);
+    parameter_ = new (&allocator_) HParameterValue(graph_->GetDexFile(), 0, 0, Primitive::kPrimInt);
+    entry_block_->AddInstruction(parameter_);
+    return_block_->AddInstruction(new (&allocator_) HReturnVoid());
+    exit_block_->AddInstruction(new (&allocator_) HExit());
+    entry_block_->AddSuccessor(return_block_);
+    return_block_->AddSuccessor(exit_block_);
+  }
+
+  /** Adds a loop nest at given position before successor. */
+  HBasicBlock* AddLoop(HBasicBlock* position, HBasicBlock* successor) {
+    HBasicBlock* header = new (&allocator_) HBasicBlock(graph_);
+    HBasicBlock* body = new (&allocator_) HBasicBlock(graph_);
+    graph_->AddBlock(header);
+    graph_->AddBlock(body);
+    // Control flow.
+    position->ReplaceSuccessor(successor, header);
+    header->AddSuccessor(body);
+    header->AddSuccessor(successor);
+    header->AddInstruction(new (&allocator_) HIf(parameter_));
+    body->AddSuccessor(header);
+    body->AddInstruction(new (&allocator_) HGoto());
+    return header;
+  }
+
+  /** Performs analysis. */
+  void PerformAnalysis() {
+    graph_->BuildDominatorTree();
+    iva_->Run();
+    loop_opt_->Run();
+  }
+
+  /** Constructs string representation of computed loop hierarchy. */
+  std::string LoopStructure() {
+    return LoopStructureRecurse(loop_opt_->top_loop_);
+  }
+
+  // Helper method
+  std::string LoopStructureRecurse(HLoopOptimization::LoopNode* node) {
+    std::string s;
+    for ( ; node != nullptr; node = node->next) {
+      s.append("[");
+      s.append(LoopStructureRecurse(node->inner));
+      s.append("]");
+    }
+    return s;
+  }
+
+  // General building fields.
+  ArenaPool pool_;
+  ArenaAllocator allocator_;
+  HGraph* graph_;
+  HInductionVarAnalysis* iva_;
+  HLoopOptimization* loop_opt_;
+
+  HBasicBlock* entry_block_;
+  HBasicBlock* return_block_;
+  HBasicBlock* exit_block_;
+
+  HInstruction* parameter_;
+};
+
+//
+// The actual tests.
+//
+
+TEST_F(LoopOptimizationTest, NoLoops) {
+  PerformAnalysis();
+  EXPECT_EQ("", LoopStructure());
+}
+
+TEST_F(LoopOptimizationTest, SingleLoop) {
+  AddLoop(entry_block_, return_block_);
+  PerformAnalysis();
+  EXPECT_EQ("[]", LoopStructure());
+}
+
+TEST_F(LoopOptimizationTest, LoopNest10) {
+  HBasicBlock* b = entry_block_;
+  HBasicBlock* s = return_block_;
+  for (int i = 0; i < 10; i++) {
+    s = AddLoop(b, s);
+    b = s->GetSuccessors()[0];
+  }
+  PerformAnalysis();
+  EXPECT_EQ("[[[[[[[[[[]]]]]]]]]]", LoopStructure());
+}
+
+TEST_F(LoopOptimizationTest, LoopSequence10) {
+  HBasicBlock* b = entry_block_;
+  HBasicBlock* s = return_block_;
+  for (int i = 0; i < 10; i++) {
+    b = AddLoop(b, s);
+    s = b->GetSuccessors()[1];
+  }
+  PerformAnalysis();
+  EXPECT_EQ("[][][][][][][][][][]", LoopStructure());
+}
+
+TEST_F(LoopOptimizationTest, LoopSequenceOfNests) {
+  HBasicBlock* b = entry_block_;
+  HBasicBlock* s = return_block_;
+  for (int i = 0; i < 10; i++) {
+    b = AddLoop(b, s);
+    s = b->GetSuccessors()[1];
+    HBasicBlock* bi = b->GetSuccessors()[0];
+    HBasicBlock* si = b;
+    for (int j = 0; j < i; j++) {
+      si = AddLoop(bi, si);
+      bi = si->GetSuccessors()[0];
+    }
+  }
+  PerformAnalysis();
+  EXPECT_EQ("[]"
+            "[[]]"
+            "[[[]]]"
+            "[[[[]]]]"
+            "[[[[[]]]]]"
+            "[[[[[[]]]]]]"
+            "[[[[[[[]]]]]]]"
+            "[[[[[[[[]]]]]]]]"
+            "[[[[[[[[[]]]]]]]]]"
+            "[[[[[[[[[[]]]]]]]]]]",
+            LoopStructure());
+}
+
+TEST_F(LoopOptimizationTest, LoopNestWithSequence) {
+  HBasicBlock* b = entry_block_;
+  HBasicBlock* s = return_block_;
+  for (int i = 0; i < 10; i++) {
+    s = AddLoop(b, s);
+    b = s->GetSuccessors()[0];
+  }
+  b = s;
+  s = b->GetSuccessors()[1];
+  for (int i = 0; i < 9; i++) {
+    b = AddLoop(b, s);
+    s = b->GetSuccessors()[1];
+  }
+  PerformAnalysis();
+  EXPECT_EQ("[[[[[[[[[[][][][][][][][][][]]]]]]]]]]", LoopStructure());
+}
+
+}  // namespace art