ART: Implement HSelect
This patch adds a new HIR instruction to Optimizing. HSelect returns
one of two inputs based on the outcome of a condition.
This is only initial implementation which:
- defines the new instruction,
- repurposes BooleanSimplifier to emit it,
- extends InstructionSimplifier to statically resolve it,
- updates existing code and tests accordingly.
Code generators currently emit fallback if/then/else code and will be
updated in follow-up CLs to use platform-specific conditional moves
when possible.
Change-Id: Ib61b17146487ebe6b55350c2b589f0b971dcaaee
diff --git a/compiler/optimizing/select_generator.h b/compiler/optimizing/select_generator.h
new file mode 100644
index 0000000..f9d6d4d
--- /dev/null
+++ b/compiler/optimizing/select_generator.h
@@ -0,0 +1,63 @@
+/*
+ * 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.
+ */
+
+/*
+ * This optimization recognizes the common diamond selection pattern and
+ * replaces it with an instance of the HSelect instruction.
+ *
+ * Recognized pattern:
+ *
+ * If [ Condition ]
+ * / \
+ * false branch true branch
+ * \ /
+ * Phi [FalseValue, TrueValue]
+ *
+ * The pattern will be simplified if `true_branch` and `false_branch` each
+ * contain at most one instruction without any side effects.
+ *
+ * Blocks are merged into one and Select replaces the If and the Phi:
+ * true branch
+ * false branch
+ * Select [FalseValue, TrueValue, Condition]
+ *
+ * Note: In order to recognize no side-effect blocks, this optimization must be
+ * run after the instruction simplifier has removed redundant suspend checks.
+ */
+
+#ifndef ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
+#define ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
+
+#include "optimization.h"
+
+namespace art {
+
+class HSelectGenerator : public HOptimization {
+ public:
+ explicit HSelectGenerator(HGraph* graph)
+ : HOptimization(graph, kSelectGeneratorPassName) {}
+
+ void Run() OVERRIDE;
+
+ static constexpr const char* kSelectGeneratorPassName = "select_generator";
+
+ private:
+ DISALLOW_COPY_AND_ASSIGN(HSelectGenerator);
+};
+
+} // namespace art
+
+#endif // ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_