Fixed bug in LICM

Rationale:
We should stop hoisting anything that can throw
as soon as something else that can do something
visible (either throw or write something) is *not*
hoisted (used to be just throw test on second part).

Bug: 32810295
Test: test-art-host
Change-Id: Id88b712a5d9e37598d0bebbd4ecf4b1d8ee787b5

diff --git a/compiler/optimizing/licm.cc b/compiler/optimizing/licm.cc
index eb2d18d..f0086fb 100644 (file)
--- a/compiler/optimizing/licm.cc
+++ b/compiler/optimizing/licm.cc
@@ -120,17 +120,17 @@ void LICM::Run() {
       }
       DCHECK(!loop_info->IsIrreducible());
 
-      // We can move an instruction that can throw only if it is the first
-      // throwing instruction in the loop. Note that the first potentially
-      // throwing instruction encountered that is not hoisted stops this
-      // optimization. Non-throwing instruction can still be hoisted.
-      bool found_first_non_hoisted_throwing_instruction_in_loop = !inner->IsLoopHeader();
+      // We can move an instruction that can throw only as long as it is the first visible
+      // instruction (throw or write) in the loop. Note that the first potentially visible
+      // instruction that is not hoisted stops this optimization. Non-throwing instructions,
+      // on the other hand, can still be hoisted.
+      bool found_first_non_hoisted_visible_instruction_in_loop = !inner->IsLoopHeader();
       for (HInstructionIterator inst_it(inner->GetInstructions());
            !inst_it.Done();
            inst_it.Advance()) {
         HInstruction* instruction = inst_it.Current();
         if (instruction->CanBeMoved()
-            && (!instruction->CanThrow() || !found_first_non_hoisted_throwing_instruction_in_loop)
+            && (!instruction->CanThrow() || !found_first_non_hoisted_visible_instruction_in_loop)
             && !instruction->GetSideEffects().MayDependOn(loop_effects)
             && InputsAreDefinedBeforeLoop(instruction)) {
           // We need to update the environment if the instruction has a loop header
@@ -142,10 +142,10 @@ void LICM::Run() {
           }
           instruction->MoveBefore(pre_header->GetLastInstruction());
           MaybeRecordStat(MethodCompilationStat::kLoopInvariantMoved);
-        } else if (instruction->CanThrow()) {
-          // If `instruction` can throw, we cannot move further instructions
-          // that can throw as well.
-          found_first_non_hoisted_throwing_instruction_in_loop = true;
+        } else if (instruction->CanThrow() || instruction->DoesAnyWrite()) {
+          // If `instruction` can do something visible (throw or write),
+          // we cannot move further instructions that can throw.
+          found_first_non_hoisted_visible_instruction_in_loop = true;
         }
       }
     }

diff --git a/test/625-checker-licm-regressions/expected.txt b/test/625-checker-licm-regressions/expected.txt
new file mode 100644 (file)
index 0000000..b0aad4d
--- /dev/null
+++ b/test/625-checker-licm-regressions/expected.txt
@@ -0,0 +1 @@
+passed

diff --git a/test/625-checker-licm-regressions/info.txt b/test/625-checker-licm-regressions/info.txt
new file mode 100644 (file)
index 0000000..10480df
--- /dev/null
+++ b/test/625-checker-licm-regressions/info.txt
@@ -0,0 +1 @@
+Regression tests on LICM.

diff --git a/test/625-checker-licm-regressions/src/Main.java b/test/625-checker-licm-regressions/src/Main.java
new file mode 100644 (file)
index 0000000..cc1e07c
--- /dev/null
+++ b/test/625-checker-licm-regressions/src/Main.java
@@ -0,0 +1,66 @@
+/*
+ * 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.
+ */
+
+/**
+ * Regression tests for LICM.
+ */
+public class Main {
+
+  static int sA;
+
+  //
+  // We cannot hoist the null check (can throw) above the field
+  // assignment (has write side effects) because that would result
+  // in throwing an exception before the assignment is done.
+  //
+  /// CHECK-START: void Main.foo(int[]) licm (before)
+  /// CHECK-DAG: LoadClass      loop:<<Loop:B\d+>> outer_loop:none
+  /// CHECK-DAG: StaticFieldSet loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: NullCheck      loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: ArrayLength    loop:<<Loop>>      outer_loop:none
+  //
+  /// CHECK-START: void Main.foo(int[]) licm (after)
+  /// CHECK-DAG: LoadClass      loop:none
+  /// CHECK-DAG: StaticFieldSet loop:<<Loop:B\d+>> outer_loop:none
+  /// CHECK-DAG: NullCheck      loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: ArrayLength    loop:<<Loop>>      outer_loop:none
+  //
+  /// CHECK-START: void Main.foo(int[]) licm (after)
+  /// CHECK-NOT: LoadClass      loop:{{B\d+}} outer_loop:none
+  static void foo(int[] arr) {
+    int j = 0;
+    do {
+      sA = 1;
+    } while (j < arr.length);
+  }
+
+  public static void main(String[] args) {
+    sA = 0;
+    try {
+      foo(null);
+    } catch (Exception e) {
+    }
+    expectEquals(1, sA);
+
+    System.out.println("passed");
+  }
+
+  private static void expectEquals(int expected, int result) {
+    if (expected != result) {
+      throw new Error("Expected: " + expected + ", found: " + result);
+    }
+  }
+}