[coro][nfc] Use Load/Store instruction APIs

[fdeazeve]

Summary

Instead of hard-coding operand indices, it is cleaner to use the APIs
provided by the Load/Store Inst classes.

llvm/lib/Transforms/Coroutines/CoroFrame.cpp

void coro::salvageDebugInfo(
   // Follow the pointer arithmetic all the way to the incoming
   // function argument and convert into a DIExpression.
   bool SkipOutermostLoad = !isa<DbgValueInst>(DVI);
   Value *Storage = DVI->getVariableLocationOp(0);
   Value *OriginalStorage = Storage;
 
   while (auto *Inst = dyn_cast_or_null<Instruction>(Storage)) {
     if (auto *LdInst = dyn_cast<LoadInst>(Inst)) {
-      Storage = LdInst->getOperand(0);
+      Storage = LdInst->getPointerOperand();
       // FIXME: This is a heuristic that works around the fact that
       // LLVM IR debug intrinsics cannot yet distinguish between
       // memory and value locations: Because a dbg.declare(alloca) is
       // implicitly a memory location no DW_OP_deref operation for the
       // last direct load from an alloca is necessary.  This condition
       // effectively drops the *last* DW_OP_deref in the expression.
       if (!SkipOutermostLoad)
         Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
     } else if (auto *StInst = dyn_cast<StoreInst>(Inst)) {
-      Storage = StInst->getOperand(0);
+      Storage = StInst->getValueOperand();
     } else {
       SmallVector<uint64_t, 16> Ops;
       SmallVector<Value *, 0> AdditionalValues;
       Value *Op = llvm::salvageDebugInfoImpl(
           *Inst, Expr ? Expr->getNumLocationOperands() : 0, Ops,
           AdditionalValues);
       if (!Op || !AdditionalValues.empty()) {
         // If salvaging failed or salvaging produced more than one location