VM: Move branch optimizations into a separate file.

runtime/vm/branch_optimizer.h

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_BRANCH_OPTIMIZER_H_
+#define VM_BRANCH_OPTIMIZER_H_
+
+#include "vm/allocation.h"
+
+namespace dart {
+
+class FlowGraph;
+class JoinEntryInstr;
+class Zone;
+class TargetEntryInstr;
+class Value;
+class BranchInstr;
+
+// Rewrite branches to eliminate materialization of boolean values after
+// inlining, and to expose other optimizations (e.g., constant folding of
+// branches, unreachable code elimination).
+class BranchSimplifier : public AllStatic {
+ public:
+  static void Simplify(FlowGraph* flow_graph);
+
+  // Replace a target entry instruction with a join entry instruction.  Does
+  // not update the original target's predecessors to point to the new block
+  // and does not replace the target in already computed block order lists.
+  static JoinEntryInstr* ToJoinEntry(Zone* zone,
+                                     TargetEntryInstr* target);
+
+ private:
+  // Match an instance of the pattern to rewrite.  See the implementation
+  // for the patterns that are handled by this pass.
+  static bool Match(JoinEntryInstr* block);
+
+  // Duplicate a branch while replacing its comparison's left and right
+  // inputs.
+  static BranchInstr* CloneBranch(Zone* zone,
+                                  BranchInstr* branch,
+                                  Value* new_left,
+                                  Value* new_right);
+};
+
+
+// Rewrite diamond control flow patterns that materialize values to use more
+// efficient branchless code patterns if such are supported on the current
+// platform.
+class IfConverter : public AllStatic {
+ public:
+  static void Simplify(FlowGraph* flow_graph);
+};
+
+}  // namespace dart
+
+#endif  // VM_BRANCH_OPTIMIZER_H_