Initiate a dead code elimination pass in the optimizing compiler.

Change-Id: Ie9db5d8e2c2c30e34145a0f7d2386b8ec58cfc4e

1 files changed, 185 insertions, 0 deletions

diff --git a/compiler/optimizing/dead_code_elimination_test.cc b/compiler/optimizing/dead_code_elimination_test.cc
new file mode 100644
index 0000000000..245bcb21d5
--- /dev/null
+++ b/compiler/optimizing/dead_code_elimination_test.cc
@@ -0,0 +1,185 @@
+/*
+ * 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 "dead_code_elimination.h"
+#include "pretty_printer.h"
+#include "graph_checker.h"
+#include "optimizing_unit_test.h"
+
+#include "gtest/gtest.h"
+
+namespace art {
+
+static void TestCode(const uint16_t* data,
+                     const std::string& expected_before,
+                     const std::string& expected_after) {
+  ArenaPool pool;
+  ArenaAllocator allocator(&pool);
+  HGraph* graph = CreateCFG(&allocator, data);
+  ASSERT_NE(graph, nullptr);
+
+  graph->BuildDominatorTree();
+  graph->TransformToSSA();
+
+  StringPrettyPrinter printer_before(graph);
+  printer_before.VisitInsertionOrder();
+  std::string actual_before = printer_before.str();
+  ASSERT_EQ(actual_before, expected_before);
+
+  DeadCodeElimination(graph).Run();
+
+  StringPrettyPrinter printer_after(graph);
+  printer_after.VisitInsertionOrder();
+  std::string actual_after = printer_after.str();
+  ASSERT_EQ(actual_after, expected_after);
+
+  SSAChecker ssa_checker(&allocator, graph);
+  ssa_checker.VisitInsertionOrder();
+  ASSERT_TRUE(ssa_checker.IsValid());
+}
+
+
+/**
+ * Small three-register program.
+ *
+ *                              16-bit
+ *                              offset
+ *                              ------
+ *     v1 <- 1                  0.      const/4 v1, #+1
+ *     v0 <- 0                  1.      const/4 v0, #+0
+ *     if v1 >= 0 goto L1       2.      if-gez v1, +3
+ *     v0 <- v1                 4.      move v0, v1
+ * L1: v2 <- v0 + v1            5.      add-int v2, v0, v1
+ *     return-void              7.      return
+ */
+TEST(DeadCodeElimination, AdditionAndConditionalJump) {
+  const uint16_t data[] = THREE_REGISTERS_CODE_ITEM(
+    Instruction::CONST_4 | 1 << 8 | 1 << 12,
+    Instruction::CONST_4 | 0 << 8 | 0 << 12,
+    Instruction::IF_GEZ | 1 << 8, 3,
+    Instruction::MOVE | 0 << 8 | 1 << 12,
+    Instruction::ADD_INT | 2 << 8, 0 | 1 << 8,
+    Instruction::RETURN_VOID);
+
+  std::string expected_before =
+    "BasicBlock 0, succ: 1\n"
+    "  3: IntConstant [15, 22, 8]\n"
+    "  5: IntConstant [22, 8]\n"
+    "  19: SuspendCheck\n"
+    "  20: Goto 1\n"
+    "BasicBlock 1, pred: 0, succ: 5, 2\n"
+    "  8: GreaterThanOrEqual(3, 5) [9]\n"
+    "  9: If(8)\n"
+    "BasicBlock 2, pred: 1, succ: 3\n"
+    "  12: Goto 3\n"
+    "BasicBlock 3, pred: 2, 5, succ: 4\n"
+    "  22: Phi(3, 5) [15]\n"
+    "  15: Add(22, 3)\n"
+    "  17: ReturnVoid\n"
+    "BasicBlock 4, pred: 3\n"
+    "  18: Exit\n"
+    "BasicBlock 5, pred: 1, succ: 3\n"
+    "  21: Goto 3\n";
+
+  diff_t expected_diff = {
+    { "  3: IntConstant [15, 22, 8]\n", "  3: IntConstant [22, 8]\n" },
+    { "  22: Phi(3, 5) [15]\n",         "  22: Phi(3, 5)\n" },
+    { "  15: Add(22, 3)\n",             removed }
+  };
+  std::string expected_after = Patch(expected_before, expected_diff);
+
+  TestCode(data, expected_before, expected_after);
+}
+
+/**
+ * Three-register program with jumps leading to the creation of many
+ * blocks.
+ *
+ * The intent of this test is to ensure that all dead instructions are
+ * actually pruned at compile-time, thanks to the (backward)
+ * post-order traversal of the the dominator tree.
+ *
+ *                              16-bit
+ *                              offset
+ *                              ------
+ *     v0 <- 0                   0.     const/4 v0, #+0
+ *     v1 <- 1                   1.     const/4 v1, #+1
+ *     v2 <- v0 + v1             2.     add-int v2, v0, v1
+ *     goto L2                   4.     goto +4
+ * L1: v1 <- v0 + 3              5.     add-int/lit16 v1, v0, #+3
+ *     goto L3                   7.     goto +4
+ * L2: v0 <- v2 + 2              8.     add-int/lit16 v0, v2, #+2
+ *     goto L1                  10.     goto +(-5)
+ * L3: v2 <- v1 + 4             11.     add-int/lit16 v2, v1, #+4
+ *     return                   13.     return-void
+ */
+TEST(DeadCodeElimination, AdditionsAndInconditionalJumps) {
+  const uint16_t data[] = THREE_REGISTERS_CODE_ITEM(
+    Instruction::CONST_4 | 0 << 8 | 0 << 12,
+    Instruction::CONST_4 | 1 << 8 | 1 << 12,
+    Instruction::ADD_INT | 2 << 8, 0 | 1 << 8,
+    Instruction::GOTO | 4 << 8,
+    Instruction::ADD_INT_LIT16 | 1 << 8 | 0 << 12, 3,
+    Instruction::GOTO | 4 << 8,
+    Instruction::ADD_INT_LIT16 | 0 << 8 | 2 << 12, 2,
+    static_cast<uint16_t>(Instruction::GOTO | -5 << 8),
+    Instruction::ADD_INT_LIT16 | 2 << 8 | 1 << 12, 4,
+    Instruction::RETURN_VOID);
+
+  std::string expected_before =
+    "BasicBlock 0, succ: 1\n"
+    "  3: IntConstant [9]\n"
+    "  5: IntConstant [9]\n"
+    "  13: IntConstant [14]\n"
+    "  18: IntConstant [19]\n"
+    "  24: IntConstant [25]\n"
+    "  29: SuspendCheck\n"
+    "  30: Goto 1\n"
+    "BasicBlock 1, pred: 0, succ: 3\n"
+    "  9: Add(3, 5) [19]\n"
+    "  11: Goto 3\n"
+    "BasicBlock 2, pred: 3, succ: 4\n"
+    "  14: Add(19, 13) [25]\n"
+    "  16: Goto 4\n"
+    "BasicBlock 3, pred: 1, succ: 2\n"
+    "  19: Add(9, 18) [14]\n"
+    "  21: SuspendCheck\n"
+    "  22: Goto 2\n"
+    "BasicBlock 4, pred: 2, succ: 5\n"
+    "  25: Add(14, 24)\n"
+    "  27: ReturnVoid\n"
+    "BasicBlock 5, pred: 4\n"
+    "  28: Exit\n";
+
+  // Expected difference after constant propagation.
+  diff_t expected_diff = {
+    { "  13: IntConstant [14]\n", removed },
+    { "  24: IntConstant [25]\n", removed },
+    { "  14: Add(19, 13) [25]\n", removed },
+    // The SuspendCheck instruction following this Add instruction
+    // inserts the latter in an environment, thus making it "used" and
+    // therefore non removable.  It ensues that some other Add and
+    // IntConstant instructions cannot be removed, as they are direct
+    // or indirect inputs of the initial Add instruction.
+    { "  19: Add(9, 18) [14]\n",  "  19: Add(9, 18) []\n" },
+    { "  25: Add(14, 24)\n",      removed },
+  };
+  std::string expected_after = Patch(expected_before, expected_diff);
+
+  TestCode(data, expected_before, expected_after);
+}
+
+}  // namespace art