[DirectX] initialize registers properties by calling addRegisterClass and computeRegisterProperties

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.

Author: farzonl

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