[DirectX] initialize registers properties by calling addRegisterClass and computeRegisterProperties (#128818)

This fixes #126784 for the DirectX backend.
This bug was marked critical for DX so it is going to go in first. At
least one register class needs to be added via `addRegisterClass` for
`RegClassForVT` to be valid.
Further for costing information used by loop unroll and other
optimizations to be valid we need to call `computeRegisterProperties`.
This change does both of these.

The test cases confirm that we can fetch costing information off of
`getRegisterInfo` and that `DirectXTargetLowering` maps `i32` typed
registers to `DXILClassRegClass`.

llvm/lib/Target/DirectX/DirectXTargetMachine.cpp

@@ -187,4 +187,7 @@ DirectXTargetMachine::getTargetTransformInfo(const Function &F) const {
 
 DirectXTargetLowering::DirectXTargetLowering(const DirectXTargetMachine &TM,
                                              const DirectXSubtarget &STI)
-    : TargetLowering(TM) {}
+    : TargetLowering(TM) {
+  addRegisterClass(MVT::i32, &dxil::DXILClassRegClass);
+  computeRegisterProperties(STI.getRegisterInfo());
+}

llvm/unittests/Target/DirectX/CMakeLists.txt

@@ -16,4 +16,5 @@ add_llvm_target_unittest(DirectXTests
   CBufferDataLayoutTests.cpp
   PointerTypeAnalysisTests.cpp
   UniqueResourceFromUseTests.cpp
+  RegisterCostTests.cpp
   )

llvm/unittests/Target/DirectX/RegisterCostTests.cpp

@@ -0,0 +1,65 @@
+//===- llvm/unittests/Target/DirectX/RegisterCostTests.cpp ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DirectXInstrInfo.h"
+#include "DirectXTargetLowering.h"
+#include "DirectXTargetMachine.h"
+#include "TargetInfo/DirectXTargetInfo.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/MC/MCTargetOptions.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::dxil;
+
+namespace {
+class RegisterCostTests : public testing::Test {
+protected:
+  DirectXInstrInfo DXInstInfo;
+  DirectXRegisterInfo RI;
+  DirectXTargetLowering *DL;
+
+  virtual void SetUp() {
+    LLVMInitializeDirectXTargetMC();
+    Target T = getTheDirectXTarget();
+    RegisterTargetMachine<DirectXTargetMachine> X(T);
+    Triple TT("dxil-pc-shadermodel6.3-library");
+    StringRef CPU = "";
+    StringRef FS = "";
+    DirectXTargetMachine TM(T, TT, CPU, FS, TargetOptions(), Reloc::Static,
+                            CodeModel::Small, CodeGenOptLevel::Default, false);
+    LLVMContext Context;
+    Function *F =
+        Function::Create(FunctionType::get(Type::getVoidTy(Context), false),
+                         Function::ExternalLinkage, 0);
+    DL = new DirectXTargetLowering(TM, *TM.getSubtargetImpl(*F));
+    delete F;
+  }
+  virtual void TearDown() { delete DL; }
+};
+
+TEST_F(RegisterCostTests, TestRepRegClassForVTSet) {
+  const TargetRegisterClass *RC = DL->getRepRegClassFor(MVT::i32);
+  EXPECT_EQ(&dxil::DXILClassRegClass, RC);
+}
+
+TEST_F(RegisterCostTests, TestTrivialCopyCostGetter) {
+
+  const TargetRegisterClass *RC = DXInstInfo.getRegisterInfo().getRegClass(0);
+  unsigned Cost = RC->getCopyCost();
+  EXPECT_EQ(1u, Cost);
+
+  RC = RI.getRegClass(0);
+  Cost = RC->getCopyCost();
+  EXPECT_EQ(1u, Cost);
+}
+} // namespace