[NFC][DXIL] Allow extra args to replaceFunctionWithOp

    - allow passing down extra arguments when lowering a directx
      intrinsic to its dxil op code

    - this allows us to not create a custom intrinsic for the
      targeted intermediate intrinsic that it lowers to and does not
      require us to write a complete custom lowering

Author: inbelic

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -106,7 +106,9 @@ class OpLowerer {
   }
 
   [[nodiscard]]
-  bool replaceFunctionWithOp(Function &F, dxil::OpCode DXILOp) {
+  bool replaceFunctionWithOp(
+      Function &F, dxil::OpCode DXILOp,
+      std::optional<SmallVector<Value *>> ExtraArgs = std::nullopt) {
     bool IsVectorArgExpansion = isVectorArgExpansion(F);
     return replaceFunction(F, [&](CallInst *CI) -> Error {
       SmallVector<Value *> Args;
@@ -117,6 +119,11 @@ class OpLowerer {
       } else
         Args.append(CI->arg_begin(), CI->arg_end());
 
+      // Append any given alias arguments
+      if (ExtraArgs) {
+        Args.append(ExtraArgs->begin(), ExtraArgs->end());
+      }
+
       Expected<CallInst *> OpCall =
           OpBuilder.tryCreateOp(DXILOp, Args, CI->getName(), F.getReturnType());
       if (Error E = OpCall.takeError())