Enable COWArrayOpts on OSSA

Additional handling of copy_value/destroy_value/load[copy]/
begin_borrow/end_borrow is needed to support OSSA.

TODO: Support handling of 2d array in the pass for OSSA.
Currently hoisting of loads and borrows are not supported in OSSA

Author: meg-gupta

include/swift/SIL/SILInstruction.h

@@ -541,6 +541,7 @@ class SILInstruction
   SILValue getOperand(unsigned Num) const {
     return getAllOperands()[Num].get();
   }
+  Operand &getOperandRef(unsigned Num) { return getAllOperands()[Num]; }
   void setOperand(unsigned Num, SILValue V) { getAllOperands()[Num].set(V); }
   void swapOperands(unsigned Num1, unsigned Num2) {
     getAllOperands()[Num1].swap(getAllOperands()[Num2]);

lib/SILOptimizer/LoopTransforms/ArrayOpt.h

@@ -125,6 +125,9 @@ class StructUseCollector {
     if (!ElementAddressUsers.empty())
       return false;
     for (SILInstruction *user : StructAddressUsers) {
+      // ignore load users
+      if (isa<LoadInst>(user))
+        continue;
       if (user != use1 && user != use2)
         return false;
     }
@@ -184,6 +187,7 @@ class StructUseCollector {
         // Found a use of the struct at the given access path.
         if (auto *LoadI = dyn_cast<LoadInst>(UseInst)) {
           StructLoads.push_back(LoadI);
+          StructAddressUsers.push_back(LoadI);
           continue;
         }