1 files changed, 120 insertions, 0 deletions
diff --git a/compiler/optimizing/loop_analysis.cc b/compiler/optimizing/loop_analysis.cc
new file mode 100644
index 0000000000..cd3bdaf016
--- /dev/null
+++ b/compiler/optimizing/loop_analysis.cc
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2018 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_analysis.h"
+
+namespace art {
+
+void LoopAnalysis::CalculateLoopBasicProperties(HLoopInformation* loop_info,
+                                                LoopAnalysisInfo* analysis_results) {
+  for (HBlocksInLoopIterator block_it(*loop_info);
+       !block_it.Done();
+       block_it.Advance()) {
+    HBasicBlock* block = block_it.Current();
+
+    for (HBasicBlock* successor : block->GetSuccessors()) {
+      if (!loop_info->Contains(*successor)) {
+        analysis_results->exits_num_++;
+      }
+    }
+
+    for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
+      HInstruction* instruction = it.Current();
+      if (MakesScalarUnrollingNonBeneficial(instruction)) {
+        analysis_results->has_instructions_preventing_scalar_unrolling_ = true;
+      }
+      analysis_results->instr_num_++;
+    }
+    analysis_results->bb_num_++;
+  }
+}
+
+class Arm64LoopHelper : public ArchDefaultLoopHelper {
+ public:
+  // Scalar loop unrolling parameters and heuristics.
+  //
+  // Maximum possible unrolling factor.
+  static constexpr uint32_t kArm64ScalarMaxUnrollFactor = 2;
+  // Loop's maximum instruction count. Loops with higher count will not be peeled/unrolled.
+  static constexpr uint32_t kArm64ScalarHeuristicMaxBodySizeInstr = 40;
+  // Loop's maximum basic block count. Loops with higher count will not be peeled/unrolled.
+  static constexpr uint32_t kArm64ScalarHeuristicMaxBodySizeBlocks = 8;
+
+  // SIMD loop unrolling parameters and heuristics.
+  //
+  // Maximum possible unrolling factor.
+  static constexpr uint32_t kArm64SimdMaxUnrollFactor = 8;
+  // Loop's maximum instruction count. Loops with higher count will not be unrolled.
+  static constexpr uint32_t kArm64SimdHeuristicMaxBodySizeInstr = 50;
+
+  bool IsLoopTooBigForScalarUnrolling(LoopAnalysisInfo* loop_analysis_info) const OVERRIDE {
+    size_t instr_num = loop_analysis_info->GetNumberOfInstructions();
+    size_t bb_num = loop_analysis_info->GetNumberOfBasicBlocks();
+    return (instr_num >= kArm64ScalarHeuristicMaxBodySizeInstr ||
+            bb_num >= kArm64ScalarHeuristicMaxBodySizeBlocks);
+  }
+
+  uint32_t GetScalarUnrollingFactor(HLoopInformation* loop_info ATTRIBUTE_UNUSED,
+                                    uint64_t trip_count) const OVERRIDE {
+    uint32_t desired_unrolling_factor = kArm64ScalarMaxUnrollFactor;
+    if (trip_count < desired_unrolling_factor || trip_count % desired_unrolling_factor != 0) {
+      return kNoUnrollingFactor;
+    }
+
+    return desired_unrolling_factor;
+  }
+
+  uint32_t GetSIMDUnrollingFactor(HBasicBlock* block,
+                                  int64_t trip_count,
+                                  uint32_t max_peel,
+                                  uint32_t vector_length) const OVERRIDE {
+    // Don't unroll with insufficient iterations.
+    // TODO: Unroll loops with unknown trip count.
+    DCHECK_NE(vector_length, 0u);
+    if (trip_count < (2 * vector_length + max_peel)) {
+      return kNoUnrollingFactor;
+    }
+    // Don't unroll for large loop body size.
+    uint32_t instruction_count = block->GetInstructions().CountSize();
+    if (instruction_count >= kArm64SimdHeuristicMaxBodySizeInstr) {
+      return kNoUnrollingFactor;
+    }
+    // Find a beneficial unroll factor with the following restrictions:
+    //  - At least one iteration of the transformed loop should be executed.
+    //  - The loop body shouldn't be "too big" (heuristic).
+
+    uint32_t uf1 = kArm64SimdHeuristicMaxBodySizeInstr / instruction_count;
+    uint32_t uf2 = (trip_count - max_peel) / vector_length;
+    uint32_t unroll_factor =
+        TruncToPowerOfTwo(std::min({uf1, uf2, kArm64SimdMaxUnrollFactor}));
+    DCHECK_GE(unroll_factor, 1u);
+    return unroll_factor;
+  }
+};
+
+ArchDefaultLoopHelper* ArchDefaultLoopHelper::Create(InstructionSet isa,
+                                                     ArenaAllocator* allocator) {
+  switch (isa) {
+    case InstructionSet::kArm64: {
+      return new (allocator) Arm64LoopHelper;
+    }
+    default: {
+      return new (allocator) ArchDefaultLoopHelper;
+    }
+  }
+}
+
+}  // namespace art