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

[Chris B via llvm-commits]

================
@@ -0,0 +1,215 @@
+//===- 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/Analysis/DXILMetadataAnalysis.h"
+#include "llvm/BinaryFormat/DXContainer.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
+#include <optional>
+
+using namespace llvm;
+using namespace llvm::dxil;
+
+static bool reportError(LLVMContext *Ctx, Twine Message,
+                        DiagnosticSeverity Severity = DS_Error) {
+  Ctx->diagnose(DiagnosticInfoGeneric(Message, Severity));
+  return true;
+}
+
+static bool parseRootFlags(LLVMContext *Ctx, ModuleRootSignature *MRS,
+                           MDNode *RootFlagNode) {
+
+  if (RootFlagNode->getNumOperands() != 2)
+    return reportError(Ctx, "Invalid format for RootFlag Element");
+
+  auto *Flag = mdconst::extract<ConstantInt>(RootFlagNode->getOperand(1));
+  MRS->Flags = Flag->getZExtValue();
+
+  return false;
+}
+
+static bool parseRootSignatureElement(LLVMContext *Ctx,
+                                      ModuleRootSignature *MRS,
+                                      MDNode *Element) {
+  MDString *ElementText = cast<MDString>(Element->getOperand(0));
+  if (ElementText == nullptr)
+    return reportError(Ctx, "Invalid format for Root Element");
+
+  RootSignatureElementKind ElementKind =
+      StringSwitch<RootSignatureElementKind>(ElementText->getString())
+          .Case("RootFlags", RootSignatureElementKind::RootFlags)
+          .Default(RootSignatureElementKind::None);
+
+  switch (ElementKind) {
+
+  case RootSignatureElementKind::RootFlags:
+    return parseRootFlags(Ctx, MRS, Element);
+  case RootSignatureElementKind::None:
+    return reportError(Ctx,
+                       "Invalid Root Element: " + ElementText->getString());
+  }
+
+  llvm_unreachable("Root signature element kind not expected.");
+}
+
+static bool parse(LLVMContext *Ctx, ModuleRootSignature *MRS, NamedMDNode *Root,
+                  const Function *EntryFunction) {
+  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 its operands and process the function,
+      signature pair.
+   */
+
+  for (const MDNode *Node : Root->operands()) {
+    if (Node->getNumOperands() != 2) {
+      HasError = reportError(
+          Ctx, "Invalid format for Root Signature Definition. Pairs "
+               "of function, root signature expected.");
+      continue;
+    }
+
+    const MDOperand &FunctionPointerMdNode = Node->getOperand(0);
+    if (FunctionPointerMdNode == nullptr) {
+      // Function was pruned during compilation.
+      continue;
+    }
----------------
llvm-beanz wrote:

nit: https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements
```suggestion
    // Function was pruned during compilation.
    if (FunctionPointerMdNode == nullptr)
      continue;
```

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