ART: Boolean simplifier

The optimization recognizes the negation pattern generated by 'javac'
and replaces it with a single condition. To this end, boolean values
are now consistently assumed to be represented by an integer.

This is a first optimization which deletes blocks from the HGraph and
does so by replacing the corresponding entries with null. Hence,
existing code can continue indexing the list of blocks with the block
ID, but must check for null when iterating over the list.

Change-Id: I7779da69cfa925c6521938ad0bcc11bc52335583

1 files changed, 74 insertions, 0 deletions

diff --git a/compiler/optimizing/boolean_simplifier.h b/compiler/optimizing/boolean_simplifier.h
new file mode 100644
index 0000000000..9fa9c5acdb
--- /dev/null
+++ b/compiler/optimizing/boolean_simplifier.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2015 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.
+ */
+
+// This optimization recognizes a common pattern where a boolean value is
+// either casted to an integer or negated by selecting from zero/one integer
+// constants with an If statement. Because boolean values are internally
+// represented as zero/one, we can safely replace the pattern with a suitable
+// condition instruction.
+
+// Example: Negating a boolean value
+//     B1:
+//       z1   ParameterValue
+//       i2   IntConstant 0
+//       i3   IntConstant 1
+//       v4   Goto B2
+//     B2:
+//       z5   NotEquals [ z1 i2 ]
+//       v6   If [ z5 ] then B3 else B4
+//     B3:
+//       v7   Goto B5
+//     B4:
+//       v8   Goto B5
+//     B5:
+//       i9   Phi [ i3 i2 ]
+//       v10  Return [ i9 ]
+// turns into
+//     B1:
+//       z1   ParameterValue
+//       i2   IntConstant 0
+//       v4   Goto B2
+//     B2:
+//       z11  Equals [ z1 i2 ]
+//       v10  Return [ z11 ]
+//     B3, B4, B5: removed
+
+// Note: in order to recognize empty blocks, this optimization must be run
+// after the instruction simplifier has removed redundant suspend checks.
+
+#ifndef ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_
+#define ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_
+
+#include "optimization.h"
+
+namespace art {
+
+class HBooleanSimplifier : public HOptimization {
+ public:
+  explicit HBooleanSimplifier(HGraph* graph)
+    : HOptimization(graph, true, kBooleanSimplifierPassName) {}
+
+  void Run() OVERRIDE;
+
+  static constexpr const char* kBooleanSimplifierPassName = "boolean_simplifier";
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(HBooleanSimplifier);
+};
+
+}  // namespace art
+
+#endif  // ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_