VM: Remove more duplicate code between AOT and JIT compiler.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index 0c7aa526cd60c97caf23d9b82f3c6a36fe7d5575..7da7ac012dabc58194248129b7ecc7603a48f452 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -305,6 +305,11 @@ class FlowGraph : public ZoneAllocated {
 
   bool IsReceiver(Definition* def) const;
 
+  // Optimize (a << b) & c pattern: if c is a positive Smi or zero, then the
+  // shift can be a truncating Smi shift-left and result is always Smi.
+  // Merge instructions (only per basic-block).
+  void TryOptimizePatterns();
+
  private:
   friend class IfConverter;
   friend class BranchSimplifier;
@@ -361,6 +366,18 @@ class FlowGraph : public ZoneAllocated {
   void ComputeIsReceiverRecursive(PhiInstr* phi,
                                   GrowableArray<PhiInstr*>* unmark) const;
 
+  void OptimizeLeftShiftBitAndSmiOp(
+      ForwardInstructionIterator* current_iterator,
+      Definition* bit_and_instr,
+      Definition* left_instr,
+      Definition* right_instr);
+
+  void TryMergeTruncDivMod(GrowableArray<BinarySmiOpInstr*>* merge_candidates);
+  void TryMergeMathUnary(GrowableArray<MathUnaryInstr*>* merge_candidates);
+
+  void AppendExtractNthOutputForMerged(Definition* instr, intptr_t ix,
+                                       Representation rep, intptr_t cid);
+
   Thread* thread_;
 
   // DiscoverBlocks computes parent_ and assigned_vars_ which are then used