[llvm-branch-commits] [llvm] [DXIL] Add support for root signature flag element in DXContainer (PR #123147)

[Damyan Pepper via llvm-branch-commits]

================
@@ -0,0 +1,159 @@
+//===- DXILRootSignature.cpp - DXIL Root Signature helper objects ----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file This file contains helper objects and APIs for working with DXIL
+///       Root Signatures.
+///
+//===----------------------------------------------------------------------===//
+#include "DXILRootSignature.h"
+#include "DirectX.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Module.h"
+#include <cstdint>
+
+using namespace llvm;
+using namespace llvm::dxil;
+
+static bool reportError(Twine Message) {
+  report_fatal_error(Message, false);
+  return true;
+}
+
+static bool parseRootFlags(ModuleRootSignature *MRS, MDNode *RootFlagNode) {
+
+  if (RootFlagNode->getNumOperands() != 2)
+    return reportError("Invalid format for RootFlag Element");
+
+  auto *Flag = mdconst::extract<ConstantInt>(RootFlagNode->getOperand(1));
+  uint32_t Value = Flag->getZExtValue();
+
+  // Root Element validation, as specified:
+  // https://github.com/llvm/wg-hlsl/blob/main/proposals/0002-root-signature-in-clang.md#validations-during-dxil-generation
+  if ((Value & ~0x80000fff) != 0)
+    return reportError("Invalid flag value for RootFlag");
+
+  MRS->Flags = Value;
+  return false;
+}
+
+static bool parseRootSignatureElement(ModuleRootSignature *MRS,
+                                      MDNode *Element) {
+  MDString *ElementText = cast<MDString>(Element->getOperand(0));
+  if (ElementText == nullptr)
+    return reportError("Invalid format for Root Element");
+
+  RootSignatureElementKind ElementKind =
+      StringSwitch<RootSignatureElementKind>(ElementText->getString())
+          .Case("RootFlags", RootSignatureElementKind::RootFlags)
+          .Case("RootConstants", RootSignatureElementKind::RootConstants)
+          .Case("RootCBV", RootSignatureElementKind::RootDescriptor)
+          .Case("RootSRV", RootSignatureElementKind::RootDescriptor)
+          .Case("RootUAV", RootSignatureElementKind::RootDescriptor)
+          .Case("Sampler", RootSignatureElementKind::RootDescriptor)
+          .Case("DescriptorTable", RootSignatureElementKind::DescriptorTable)
+          .Case("StaticSampler", RootSignatureElementKind::StaticSampler)
+          .Default(RootSignatureElementKind::None);
+
+  switch (ElementKind) {
+
+  case RootSignatureElementKind::RootFlags: {
+    return parseRootFlags(MRS, Element);
+    break;
+  }
+
+  case RootSignatureElementKind::RootConstants:
+  case RootSignatureElementKind::RootDescriptor:
+  case RootSignatureElementKind::DescriptorTable:
+  case RootSignatureElementKind::StaticSampler:
+  case RootSignatureElementKind::None:
+    return reportError("Invalid Root Element: " + ElementText->getString());
+    break;
+  }
+
+  return true;
+}
+
+bool ModuleRootSignature::parse(int32_t Version, NamedMDNode *Root) {
+  this->Version = Version;
+  bool HasError = false;
+
+  /** Root Signature are specified as following in the metadata:
+
+      !dx.rootsignatures = !{!2} ; list of function/root signature pairs
+      !2 = !{ ptr @main, !3 } ; function, root signature
+      !3 = !{ !4, !5, !6, !7 } ; list of root signature elements
+
+      So for each MDNode inside dx.rootsignatures NamedMDNode
+      (the Root parameter of this function), the parsing process needs
+      to loop through each of it's operand and process the pairs function
+      signature pair.
+   */
+
+  for (unsigned int Sid = 0; Sid < Root->getNumOperands(); Sid++) {
+    MDNode *Node = dyn_cast<MDNode>(Root->getOperand(Sid));
+
+    if (Node == nullptr || Node->getNumOperands() != 2)
+      return reportError("Invalid format for Root Signature Definition. Pairs "
+                         "of function, root signature expected.");
+
+    // Get the Root Signature Description from the function signature pair.
+    MDNode *RS = dyn_cast<MDNode>(Node->getOperand(1).get());
----------------
damyanp wrote:

```
    MDNode *RS = dyn_cast<MDNode>(Node->getOperand(1).get());
```

If I change this `dyn_cast` to `cast` then the tests still pass.  Test hole?  Or maybe `cast` is sufficient here?  

I'm not sure how to construct a metadata entry here that isn't an MDNode so maybe it just isn't possible to generate something that isn't an MDNode?

https://github.com/llvm/llvm-project/pull/123147