[clang] [llvm] [HLSL][RootSignature] Implement parsing of `RootParamter`s (PR #121803)

Finn Plummer via llvm-commits llvm-commits at lists.llvm.org
Mon Jan 6 09:16:27 PST 2025


https://github.com/inbelic created https://github.com/llvm/llvm-project/pull/121803

```
- Implement the ParseRootParameter methods in ParseHLSLRootSignature
- Define the in-memory represenation of the various RootParameters and adds
it to the RootElement structure
- Add testing of valid inputs to ParseHLSLRootSignatureTest.cpp
```
Part of the work for #120472

>From bee90e659e647df21d1f1e65f95fffefa57eadce Mon Sep 17 00:00:00 2001
From: Finn Plummer <canadienfinn at gmail.com>
Date: Mon, 6 Jan 2025 16:21:33 +0000
Subject: [PATCH 1/2] [HLSL] Implement parsing of `RootFlags`

- Define the Parser class that will contain all the parsing methods in
ParseHLSLRootSignature.h
- Implement the dispatch behaviour of Parse and ParseRootElement in
ParseHLSLRootSignature.cpp
- Define the general in-memory datastructure of a RootElement that will
be a union of the various RootElement types

- Implement the ParseRootFlags methods in ParseHLSLRootSignature
- Define the in-memory represenation of the RootFlag and adds it to the
RootElement structure
- Add testing of valid inputs to ParseHLSLRootSignatureTest.cpp
---
 .../clang/Sema/ParseHLSLRootSignature.h       |  63 ++++++++
 clang/lib/Sema/CMakeLists.txt                 |   1 +
 clang/lib/Sema/ParseHLSLRootSignature.cpp     | 139 ++++++++++++++++++
 clang/unittests/Sema/CMakeLists.txt           |   1 +
 .../Sema/ParseHLSLRootSignatureTest.cpp       |  58 ++++++++
 .../llvm/Frontend/HLSL/HLSLRootSignature.h    |  88 +++++++++++
 6 files changed, 350 insertions(+)
 create mode 100644 clang/include/clang/Sema/ParseHLSLRootSignature.h
 create mode 100644 clang/lib/Sema/ParseHLSLRootSignature.cpp
 create mode 100644 clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
 create mode 100644 llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h

diff --git a/clang/include/clang/Sema/ParseHLSLRootSignature.h b/clang/include/clang/Sema/ParseHLSLRootSignature.h
new file mode 100644
index 00000000000000..7d1799e22b515c
--- /dev/null
+++ b/clang/include/clang/Sema/ParseHLSLRootSignature.h
@@ -0,0 +1,63 @@
+//===--- ParseHLSLRootSignature.h -------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the ParseHLSLRootSignature interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_SEMA_PARSEHLSLROOTSIGNATURE_H
+#define LLVM_CLANG_SEMA_PARSEHLSLROOTSIGNATURE_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
+
+#include "llvm/Frontend/HLSL/HLSLRootSignature.h"
+
+namespace llvm {
+namespace hlsl {
+namespace root_signature {
+
+class Parser {
+public:
+  Parser(StringRef Signature, SmallVector<RootElement> *Elements)
+      : Buffer(Signature), Elements(Elements) {}
+
+  // Consumes the internal buffer as a list of root elements and will
+  // emplace their in-memory representation onto the back of Elements.
+  //
+  // It will consume until it successfully reaches the end of the buffer,
+  // or until the first error is encountered. The return value denotes if
+  // there was a failure.
+  bool Parse();
+
+private:
+  bool ReportError();
+
+  // RootElements parse methods
+  bool ParseRootElement();
+
+  bool ParseRootFlags();
+  // Enum methods
+  template <typename EnumType>
+  bool ParseEnum(SmallVector<std::pair<StringLiteral, EnumType>> Mapping,
+                 EnumType &Enum);
+  bool ParseRootFlag(RootFlags &Flag);
+
+  // Internal state used when parsing
+  StringRef Buffer;
+  SmallVector<RootElement> *Elements;
+
+  StringRef Token;
+};
+
+} // namespace root_signature
+} // namespace hlsl
+} // namespace llvm
+
+#endif // LLVM_CLANG_SEMA_PARSEHLSLROOTSIGNATURE_H
diff --git a/clang/lib/Sema/CMakeLists.txt b/clang/lib/Sema/CMakeLists.txt
index 719c3a9312ec15..7141bb42eb4363 100644
--- a/clang/lib/Sema/CMakeLists.txt
+++ b/clang/lib/Sema/CMakeLists.txt
@@ -24,6 +24,7 @@ add_clang_library(clangSema
   JumpDiagnostics.cpp
   MultiplexExternalSemaSource.cpp
   ParsedAttr.cpp
+  ParseHLSLRootSignature.cpp
   Scope.cpp
   ScopeInfo.cpp
   Sema.cpp
diff --git a/clang/lib/Sema/ParseHLSLRootSignature.cpp b/clang/lib/Sema/ParseHLSLRootSignature.cpp
new file mode 100644
index 00000000000000..e4592ea1937178
--- /dev/null
+++ b/clang/lib/Sema/ParseHLSLRootSignature.cpp
@@ -0,0 +1,139 @@
+#include "clang/Sema/ParseHLSLRootSignature.h"
+
+namespace llvm {
+namespace hlsl {
+namespace root_signature {
+
+// TODO: Hook up with Sema to properly report semantic/validation errors
+bool Parser::ReportError() { return true; }
+
+bool Parser::ParseRootFlags() {
+  // Set to RootFlags::None and skip whitespace to catch when we have RootFlags(
+  // )
+  RootFlags Flags = RootFlags::None;
+  Buffer = Buffer.drop_while(isspace);
+  StringLiteral Prefix = "";
+
+  // Loop until we reach the end of the rootflags
+  while (!Buffer.starts_with(")")) {
+    // Trim expected | when more than 1 flag
+    if (!Buffer.consume_front(Prefix))
+      return ReportError();
+    Prefix = "|";
+
+    // Remove any whitespace
+    Buffer = Buffer.drop_while(isspace);
+
+    RootFlags CurFlag;
+    if (ParseRootFlag(CurFlag))
+      return ReportError();
+    Flags |= CurFlag;
+
+    // Remove any whitespace
+    Buffer = Buffer.drop_while(isspace);
+  }
+
+  // Create and push the root element on the parsed elements
+  Elements->push_back(RootElement(Flags));
+  return false;
+}
+
+template <typename EnumType>
+bool Parser::ParseEnum(SmallVector<std::pair<StringLiteral, EnumType>> Mapping,
+                       EnumType &Enum) {
+  // Retrieve enum
+  Token = Buffer.take_while([](char C) { return isalnum(C) || C == '_'; });
+  Buffer = Buffer.drop_front(Token.size());
+
+  // Try to get the case-insensitive enum
+  auto Switch = llvm::StringSwitch<std::optional<EnumType>>(Token);
+  for (auto Pair : Mapping)
+    Switch.CaseLower(Pair.first, Pair.second);
+  auto MaybeEnum = Switch.Default(std::nullopt);
+  if (!MaybeEnum)
+    return true;
+  Enum = *MaybeEnum;
+
+  return false;
+}
+
+bool Parser::ParseRootFlag(RootFlags &Flag) {
+  SmallVector<std::pair<StringLiteral, RootFlags>> Mapping = {
+      {"0", RootFlags::None},
+      {"ALLOW_INPUT_ASSEMBLER_INPUT_LAYOUT",
+       RootFlags::AllowInputAssemblerInputLayout},
+      {"DENY_VERTEX_SHADER_ROOT_ACCESS", RootFlags::DenyVertexShaderRootAccess},
+      {"DENY_HULL_SHADER_ROOT_ACCESS", RootFlags::DenyHullShaderRootAccess},
+      {"DENY_DOMAIN_SHADER_ROOT_ACCESS", RootFlags::DenyDomainShaderRootAccess},
+      {"DENY_GEOMETRY_SHADER_ROOT_ACCESS",
+       RootFlags::DenyGeometryShaderRootAccess},
+      {"DENY_PIXEL_SHADER_ROOT_ACCESS", RootFlags::DenyPixelShaderRootAccess},
+      {"ALLOW_STREAM_OUTPUT", RootFlags::AllowStreamOutput},
+      {"LOCAL_ROOT_SIGNATURE", RootFlags::LocalRootSignature},
+      {"DENY_AMPLIFICATION_SHADER_ROOT_ACCESS",
+       RootFlags::DenyAmplificationShaderRootAccess},
+      {"DENY_MESH_SHADER_ROOT_ACCESS", RootFlags::DenyMeshShaderRootAccess},
+      {"CBV_SRV_UAV_HEAP_DIRECTLY_INDEXED",
+       RootFlags::CBVSRVUAVHeapDirectlyIndexed},
+      {"SAMPLER_HEAP_DIRECTLY_INDEXED", RootFlags::SamplerHeapDirectlyIndexed},
+      {"AllowLowTierReservedHwCbLimit",
+       RootFlags::AllowLowTierReservedHwCbLimit},
+  };
+
+  return ParseEnum<RootFlags>(Mapping, Flag);
+}
+
+bool Parser::ParseRootElement() {
+  // Define different ParserMethods to use StringSwitch for dispatch
+  enum class ParserMethod {
+    ReportError,
+    ParseRootFlags,
+  };
+
+  // Retreive which method should be used
+  auto Method = llvm::StringSwitch<ParserMethod>(Token)
+                    .Case("RootFlags", ParserMethod::ParseRootFlags)
+                    .Default(ParserMethod::ReportError);
+
+  // Dispatch on the correct method
+  switch (Method) {
+  case ParserMethod::ReportError:
+    return ReportError();
+  case ParserMethod::ParseRootFlags:
+    return ParseRootFlags();
+  }
+}
+
+// Parser entry point function
+bool Parser::Parse() {
+  StringLiteral Prefix = "";
+  while (!Buffer.empty()) {
+    // Trim expected comma when more than 1 root element
+    if (!Buffer.consume_front(Prefix))
+      return ReportError();
+    Prefix = ",";
+
+    // Remove any whitespace
+    Buffer = Buffer.drop_while(isspace);
+
+    // Retrieve the root element identifier
+    auto Split = Buffer.split('(');
+    Token = Split.first;
+    Buffer = Split.second;
+
+    // Dispatch to the applicable root element parser
+    if (ParseRootElement())
+      return true;
+
+    // Then we can clean up the remaining ")"
+    if (!Buffer.consume_front(")"))
+      return ReportError();
+  }
+
+  // All input has been correctly parsed
+  return false;
+}
+
+} // namespace root_signature
+} // namespace hlsl
+} // namespace llvm
diff --git a/clang/unittests/Sema/CMakeLists.txt b/clang/unittests/Sema/CMakeLists.txt
index 7ded562e8edfa5..f382f8b1235306 100644
--- a/clang/unittests/Sema/CMakeLists.txt
+++ b/clang/unittests/Sema/CMakeLists.txt
@@ -7,6 +7,7 @@ add_clang_unittest(SemaTests
   ExternalSemaSourceTest.cpp
   CodeCompleteTest.cpp
   GslOwnerPointerInference.cpp
+  ParseHLSLRootSignatureTest.cpp
   SemaLookupTest.cpp
   SemaNoloadLookupTest.cpp
   )
diff --git a/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp b/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
new file mode 100644
index 00000000000000..0e7feb50871669
--- /dev/null
+++ b/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
@@ -0,0 +1,58 @@
+//=== ParseHLSLRootSignatureTest.cpp - Parse Root Signature tests ---------===//
+//
+// 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 "clang/Sema/ParseHLSLRootSignature.h"
+#include "gtest/gtest.h"
+
+using namespace llvm::hlsl::root_signature;
+
+namespace {
+
+TEST(ParseHLSLRootSignature, EmptyRootFlags) {
+  llvm::StringRef RootFlagString = " RootFlags()";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(RootFlagString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+  ASSERT_EQ(RootFlags::None, RootElements[0].Flags);
+}
+
+TEST(ParseHLSLRootSignature, RootFlagsNone) {
+  llvm::StringRef RootFlagString = " RootFlags(0)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(RootFlagString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+  ASSERT_EQ(RootFlags::None, RootElements[0].Flags);
+}
+
+TEST(ParseHLSLRootSignature, ValidRootFlags) {
+  // Test that the flags are all captured and that they are case insensitive
+  llvm::StringRef RootFlagString = " RootFlags( "
+                                   " ALLOW_INPUT_ASSEMBLER_INPUT_LAYOUT"
+                                   "| deny_vertex_shader_root_access"
+                                   "| DENY_HULL_SHADER_ROOT_ACCESS"
+                                   "| deny_domain_shader_root_access"
+                                   "| DENY_GEOMETRY_SHADER_ROOT_ACCESS"
+                                   "| deny_pixel_shader_root_access"
+                                   "| ALLOW_STREAM_OUTPUT"
+                                   "| LOCAL_ROOT_SIGNATURE"
+                                   "| deny_amplification_shader_root_access"
+                                   "| DENY_MESH_SHADER_ROOT_ACCESS"
+                                   "| cbv_srv_uav_heap_directly_indexed"
+                                   "| SAMPLER_HEAP_DIRECTLY_INDEXED"
+                                   "| AllowLowTierReservedHwCbLimit )";
+
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(RootFlagString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+  ASSERT_EQ(RootFlags::ValidFlags, RootElements[0].Flags);
+}
+
+} // anonymous namespace
diff --git a/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h b/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
new file mode 100644
index 00000000000000..a17ebffc7a6bf2
--- /dev/null
+++ b/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
@@ -0,0 +1,88 @@
+//===- HLSLRootSignature.h - HLSL 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 for working with HLSL Root
+/// Signatures.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+#define LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+
+#include <stdint.h>
+
+#include "llvm/Support/Endian.h"
+
+namespace llvm {
+namespace hlsl {
+namespace root_signature {
+
+// This is a copy from DebugInfo/CodeView/CodeView.h
+#define RS_DEFINE_ENUM_CLASS_FLAGS_OPERATORS(Class)                            \
+  inline Class operator|(Class a, Class b) {                                   \
+    return static_cast<Class>(llvm::to_underlying(a) |                         \
+                              llvm::to_underlying(b));                         \
+  }                                                                            \
+  inline Class operator&(Class a, Class b) {                                   \
+    return static_cast<Class>(llvm::to_underlying(a) &                         \
+                              llvm::to_underlying(b));                         \
+  }                                                                            \
+  inline Class operator~(Class a) {                                            \
+    return static_cast<Class>(~llvm::to_underlying(a));                        \
+  }                                                                            \
+  inline Class &operator|=(Class &a, Class b) {                                \
+    a = a | b;                                                                 \
+    return a;                                                                  \
+  }                                                                            \
+  inline Class &operator&=(Class &a, Class b) {                                \
+    a = a & b;                                                                 \
+    return a;                                                                  \
+  }
+
+// Various enumerations and flags
+
+enum class RootFlags : uint32_t {
+  None = 0,
+  AllowInputAssemblerInputLayout = 0x1,
+  DenyVertexShaderRootAccess = 0x2,
+  DenyHullShaderRootAccess = 0x4,
+  DenyDomainShaderRootAccess = 0x8,
+  DenyGeometryShaderRootAccess = 0x10,
+  DenyPixelShaderRootAccess = 0x20,
+  AllowStreamOutput = 0x40,
+  LocalRootSignature = 0x80,
+  DenyAmplificationShaderRootAccess = 0x100,
+  DenyMeshShaderRootAccess = 0x200,
+  CBVSRVUAVHeapDirectlyIndexed = 0x400,
+  SamplerHeapDirectlyIndexed = 0x800,
+  AllowLowTierReservedHwCbLimit = 0x80000000,
+  ValidFlags = 0x80000fff
+};
+RS_DEFINE_ENUM_CLASS_FLAGS_OPERATORS(RootFlags)
+
+// Define the in-memory layout structures
+
+struct RootElement {
+  enum class ElementType {
+    RootFlags,
+  };
+
+  ElementType Tag;
+  union {
+    RootFlags Flags;
+  };
+
+  // Constructors
+  RootElement(RootFlags Flags) : Tag(ElementType::RootFlags), Flags(Flags) {}
+};
+
+} // namespace root_signature
+} // namespace hlsl
+} // namespace llvm
+
+#endif // LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H

>From 8ed0186a9e3a9cf2af45eb102dff77fabcc4cb97 Mon Sep 17 00:00:00 2001
From: Finn Plummer <canadienfinn at gmail.com>
Date: Mon, 6 Jan 2025 17:02:07 +0000
Subject: [PATCH 2/2] [HLSL][RootSignature] Implement parsing of
 `RootParamter`s

- Implement the ParseRootParameter methods in ParseHLSLRootSignature
- Define the in-memory represenation of the RootFlag and adds it to the
RootElement structure
- Add testing of valid inputs to ParseHLSLRootSignatureTest.cpp
---
 .../clang/Sema/ParseHLSLRootSignature.h       |  12 ++
 clang/lib/Sema/ParseHLSLRootSignature.cpp     | 176 ++++++++++++++++++
 .../Sema/ParseHLSLRootSignatureTest.cpp       |  98 ++++++++++
 .../llvm/Frontend/HLSL/HLSLRootSignature.h    |  45 +++++
 4 files changed, 331 insertions(+)

diff --git a/clang/include/clang/Sema/ParseHLSLRootSignature.h b/clang/include/clang/Sema/ParseHLSLRootSignature.h
index 7d1799e22b515c..f06e02800e5f5f 100644
--- a/clang/include/clang/Sema/ParseHLSLRootSignature.h
+++ b/clang/include/clang/Sema/ParseHLSLRootSignature.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_SEMA_PARSEHLSLROOTSIGNATURE_H
 #define LLVM_CLANG_SEMA_PARSEHLSLROOTSIGNATURE_H
 
+#include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -43,11 +44,22 @@ class Parser {
   bool ParseRootElement();
 
   bool ParseRootFlags();
+  bool ParseRootParameter();
+
+  // Helper methods
+  bool ParseAssign();
+  bool ParseComma();
+  bool ParseOptComma();
+  bool ParseRegister(Register &);
+  bool ParseUnsignedInt(uint32_t &Number);
+
   // Enum methods
   template <typename EnumType>
   bool ParseEnum(SmallVector<std::pair<StringLiteral, EnumType>> Mapping,
                  EnumType &Enum);
+  bool ParseRootDescriptorFlag(RootDescriptorFlags &Flag);
   bool ParseRootFlag(RootFlags &Flag);
+  bool ParseVisibility(ShaderVisibility &Visibility);
 
   // Internal state used when parsing
   StringRef Buffer;
diff --git a/clang/lib/Sema/ParseHLSLRootSignature.cpp b/clang/lib/Sema/ParseHLSLRootSignature.cpp
index e4592ea1937178..72bc5b1be32625 100644
--- a/clang/lib/Sema/ParseHLSLRootSignature.cpp
+++ b/clang/lib/Sema/ParseHLSLRootSignature.cpp
@@ -38,6 +38,148 @@ bool Parser::ParseRootFlags() {
   return false;
 }
 
+bool Parser::ParseRootParameter() {
+  RootParameter Parameter;
+  Parameter.Type = llvm::StringSwitch<RootType>(Token)
+                       .Case("CBV", RootType::CBV)
+                       .Case("SRV", RootType::SRV)
+                       .Case("UAV", RootType::UAV)
+                       .Case("RootConstants", RootType::Constants);
+                       // Will never reach here as Token was just verified in dispatch
+
+  // Remove any whitespace
+  Buffer = Buffer.drop_while(isspace);
+
+  // Retreive mandatory num32BitConstant arg for RootConstants
+  if (Parameter.Type == RootType::Constants) {
+    if (!Buffer.consume_front("num32BitConstants"))
+      return ReportError();
+
+    if (ParseAssign())
+      return ReportError();
+
+    if (ParseUnsignedInt(Parameter.Num32BitConstants))
+      return ReportError();
+
+    if (ParseOptComma())
+      return ReportError();
+  }
+
+  // Retrieve mandatory register
+  if (ParseRegister(Parameter.Register))
+    return true;
+
+  if (ParseOptComma())
+    return ReportError();
+
+  // Parse common optional space arg
+  if (Buffer.consume_front("space")) {
+    if (ParseAssign())
+      return ReportError();
+
+    if (ParseUnsignedInt(Parameter.Space))
+      return ReportError();
+
+    if (ParseOptComma())
+      return ReportError();
+  }
+
+  // Parse common optional visibility arg
+  if (Buffer.consume_front("visibility")) {
+    if (ParseAssign())
+      return ReportError();
+
+    if (ParseVisibility(Parameter.Visibility))
+      return ReportError();
+
+    if (ParseOptComma())
+      return ReportError();
+  }
+
+  // Retreive optional flags arg for non-RootConstants
+  if (Parameter.Type != RootType::Constants && Buffer.consume_front("flags")) {
+    if (ParseAssign())
+      return ReportError();
+
+    if (ParseRootDescriptorFlag(Parameter.Flags))
+      return ReportError();
+
+    // Remove trailing whitespace
+    Buffer = Buffer.drop_while(isspace);
+  }
+
+  // Create and push the root element on the parsed elements
+  Elements->push_back(RootElement(Parameter));
+  return false;
+}
+
+// Helper Parser methods
+
+// Parses " = " with varying whitespace
+bool Parser::ParseAssign() {
+  Buffer = Buffer.drop_while(isspace);
+  if (!Buffer.starts_with('='))
+    return true;
+  Buffer = Buffer.drop_front();
+  Buffer = Buffer.drop_while(isspace);
+  return false;
+}
+
+// Parses ", " with varying whitespace
+bool Parser::ParseComma() {
+  if (!Buffer.starts_with(','))
+    return true;
+  Buffer = Buffer.drop_front();
+  Buffer = Buffer.drop_while(isspace);
+  return false;
+}
+
+// Parses ", " if possible. When successful we expect another parameter, and
+// return no error, otherwise we expect that we should be at the end of the
+// root element and return an error if this isn't the case
+bool Parser::ParseOptComma() {
+  if (!ParseComma())
+    return false;
+  Buffer = Buffer.drop_while(isspace);
+  return !Buffer.starts_with(')');
+}
+
+bool Parser::ParseRegister(Register &Register) {
+  // Parse expected register type ('b', 't', 'u', 's')
+  if (Buffer.empty())
+    return ReportError();
+
+  // Get type character
+  Token = Buffer.take_front();
+  Buffer = Buffer.drop_front();
+
+  auto MaybeType = llvm::StringSwitch<std::optional<RegisterType>>(Token)
+                       .Case("b", RegisterType::BReg)
+                       .Case("t", RegisterType::TReg)
+                       .Case("u", RegisterType::UReg)
+                       .Case("s", RegisterType::SReg)
+                       .Default(std::nullopt);
+  if (!MaybeType)
+    return ReportError();
+  Register.ViewType = *MaybeType;
+
+  if (ParseUnsignedInt(Register.Number))
+    return ReportError();
+
+  return false;
+}
+
+// Parses "[0-9+]" as an unsigned int
+bool Parser::ParseUnsignedInt(uint32_t &Number) {
+  StringRef NumString = Buffer.take_while(isdigit);
+  APInt X = APInt(32, 0);
+  if (NumString.getAsInteger(/*radix=*/10, X))
+    return true;
+  Number = X.getZExtValue();
+  Buffer = Buffer.drop_front(NumString.size());
+  return false;
+}
+
 template <typename EnumType>
 bool Parser::ParseEnum(SmallVector<std::pair<StringLiteral, EnumType>> Mapping,
                        EnumType &Enum) {
@@ -57,6 +199,18 @@ bool Parser::ParseEnum(SmallVector<std::pair<StringLiteral, EnumType>> Mapping,
   return false;
 }
 
+bool Parser::ParseRootDescriptorFlag(RootDescriptorFlags &Flag) {
+  SmallVector<std::pair<StringLiteral, RootDescriptorFlags>> Mapping = {
+      {"0", RootDescriptorFlags::None},
+      {"DATA_VOLATILE", RootDescriptorFlags::DataVolatile},
+      {"DATA_STATIC_WHILE_SET_AT_EXECUTE",
+       RootDescriptorFlags::DataStaticWhileSetAtExecute},
+      {"DATA_STATIC", RootDescriptorFlags::DataStatic},
+  };
+
+  return ParseEnum<RootDescriptorFlags>(Mapping, Flag);
+}
+
 bool Parser::ParseRootFlag(RootFlags &Flag) {
   SmallVector<std::pair<StringLiteral, RootFlags>> Mapping = {
       {"0", RootFlags::None},
@@ -83,16 +237,36 @@ bool Parser::ParseRootFlag(RootFlags &Flag) {
   return ParseEnum<RootFlags>(Mapping, Flag);
 }
 
+bool Parser::ParseVisibility(ShaderVisibility &Visibility) {
+  SmallVector<std::pair<StringLiteral, ShaderVisibility>> Mapping = {
+      {"SHADER_VISIBILITY_ALL", ShaderVisibility::All},
+      {"SHADER_VISIBILITY_VERTEX", ShaderVisibility::Vertex},
+      {"SHADER_VISIBILITY_HULL", ShaderVisibility::Hull},
+      {"SHADER_VISIBILITY_DOMAIN", ShaderVisibility::Domain},
+      {"SHADER_VISIBILITY_GEOMETRY", ShaderVisibility::Geometry},
+      {"SHADER_VISIBILITY_PIXEL", ShaderVisibility::Pixel},
+      {"SHADER_VISIBILITY_AMPLIFICATION", ShaderVisibility::Amplification},
+      {"SHADER_VISIBILITY_MESH", ShaderVisibility::Mesh},
+  };
+
+  return ParseEnum<ShaderVisibility>(Mapping, Visibility);
+}
+
 bool Parser::ParseRootElement() {
   // Define different ParserMethods to use StringSwitch for dispatch
   enum class ParserMethod {
     ReportError,
     ParseRootFlags,
+    ParseRootParameter,
   };
 
   // Retreive which method should be used
   auto Method = llvm::StringSwitch<ParserMethod>(Token)
                     .Case("RootFlags", ParserMethod::ParseRootFlags)
+                    .Case("RootConstants", ParserMethod::ParseRootParameter)
+                    .Case("CBV", ParserMethod::ParseRootParameter)
+                    .Case("SRV", ParserMethod::ParseRootParameter)
+                    .Case("UAV", ParserMethod::ParseRootParameter)
                     .Default(ParserMethod::ReportError);
 
   // Dispatch on the correct method
@@ -101,6 +275,8 @@ bool Parser::ParseRootElement() {
     return ReportError();
   case ParserMethod::ParseRootFlags:
     return ParseRootFlags();
+  case ParserMethod::ParseRootParameter:
+    return ParseRootParameter();
   }
 }
 
diff --git a/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp b/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
index 0e7feb50871669..eefe20293732ad 100644
--- a/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
+++ b/clang/unittests/Sema/ParseHLSLRootSignatureTest.cpp
@@ -55,4 +55,102 @@ TEST(ParseHLSLRootSignature, ValidRootFlags) {
   ASSERT_EQ(RootFlags::ValidFlags, RootElements[0].Flags);
 }
 
+TEST(ParseHLSLRootSignature, MandatoryRootConstant) {
+  llvm::StringRef RootFlagString = "RootConstants(num32BitConstants = 4, b42)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(RootFlagString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::Constants, Parameter.Type);
+  ASSERT_EQ(RegisterType::BReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)42, Parameter.Register.Number);
+  ASSERT_EQ((uint32_t)4, Parameter.Num32BitConstants);
+  ASSERT_EQ((uint32_t)0, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::All, Parameter.Visibility);
+}
+
+TEST(ParseHLSLRootSignature, OptionalRootConstant) {
+  llvm::StringRef RootFlagString =
+      "RootConstants(num32BitConstants = 4, b42, space = 4, visibility = "
+      "SHADER_VISIBILITY_DOMAIN)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(RootFlagString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::Constants, Parameter.Type);
+  ASSERT_EQ(RegisterType::BReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)42, Parameter.Register.Number);
+  ASSERT_EQ((uint32_t)4, Parameter.Num32BitConstants);
+  ASSERT_EQ((uint32_t)4, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::Domain, Parameter.Visibility);
+}
+
+TEST(ParseHLSLRootSignature, DefaultRootCBV) {
+  llvm::StringRef ViewsString = "CBV(b0)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(ViewsString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::CBV, Parameter.Type);
+  ASSERT_EQ(RegisterType::BReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)0, Parameter.Register.Number);
+  ASSERT_EQ(RootDescriptorFlags::None, Parameter.Flags);
+  ASSERT_EQ((uint32_t)0, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::All, Parameter.Visibility);
+}
+
+TEST(ParseHLSLRootSignature, SampleRootCBV) {
+  llvm::StringRef ViewsString = "CBV(b982374, space = 1, flags = DATA_STATIC)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(ViewsString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::CBV, Parameter.Type);
+  ASSERT_EQ(RegisterType::BReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)982374, Parameter.Register.Number);
+  ASSERT_EQ(RootDescriptorFlags::DataStatic, Parameter.Flags);
+  ASSERT_EQ((uint32_t)1, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::All, Parameter.Visibility);
+}
+
+TEST(ParseHLSLRootSignature, SampleRootSRV) {
+  llvm::StringRef ViewsString = "SRV(t3, visibility = SHADER_VISIBILITY_MESH, "
+                                "flags = Data_Static_While_Set_At_Execute)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(ViewsString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::SRV, Parameter.Type);
+  ASSERT_EQ(RegisterType::TReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)3, Parameter.Register.Number);
+  ASSERT_EQ(RootDescriptorFlags::DataStaticWhileSetAtExecute, Parameter.Flags);
+  ASSERT_EQ((uint32_t)0, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::Mesh, Parameter.Visibility);
+}
+
+TEST(ParseHLSLRootSignature, SampleRootUAV) {
+  llvm::StringRef ViewsString = "UAV(u0, flags = DATA_VOLATILE)";
+  llvm::SmallVector<RootElement> RootElements;
+  Parser Parser(ViewsString, &RootElements);
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ(RootElements.size(), (unsigned long)1);
+
+  RootParameter Parameter = RootElements[0].Parameter;
+  ASSERT_EQ(RootType::UAV, Parameter.Type);
+  ASSERT_EQ(RegisterType::UReg, Parameter.Register.ViewType);
+  ASSERT_EQ((uint32_t)0, Parameter.Register.Number);
+  ASSERT_EQ(RootDescriptorFlags::DataVolatile, Parameter.Flags);
+  ASSERT_EQ((uint32_t)0, Parameter.Space);
+  ASSERT_EQ(ShaderVisibility::All, Parameter.Visibility);
+}
 } // anonymous namespace
diff --git a/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h b/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
index a17ebffc7a6bf2..61fd47bbb48ab1 100644
--- a/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
+++ b/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
@@ -65,20 +65,65 @@ enum class RootFlags : uint32_t {
 };
 RS_DEFINE_ENUM_CLASS_FLAGS_OPERATORS(RootFlags)
 
+enum class RootDescriptorFlags : unsigned {
+  None = 0,
+  DataVolatile = 0x2,
+  DataStaticWhileSetAtExecute = 0x4,
+  DataStatic = 0x8,
+  ValidFlags = 0xe
+};
+RS_DEFINE_ENUM_CLASS_FLAGS_OPERATORS(RootDescriptorFlags)
+
+enum class ShaderVisibility {
+  All = 0,
+  Vertex = 1,
+  Hull = 2,
+  Domain = 3,
+  Geometry = 4,
+  Pixel = 5,
+  Amplification = 6,
+  Mesh = 7,
+};
+
 // Define the in-memory layout structures
 
+// Models the different registers: bReg | tReg | uReg | sReg
+enum class RegisterType { BReg, TReg, UReg, SReg };
+struct Register {
+  RegisterType ViewType;
+  uint32_t Number;
+};
+
+// Models RootConstants | RootCBV | RootSRV | RootUAV collecting like
+// parameters
+enum class RootType { CBV, SRV, UAV, Constants };
+struct RootParameter {
+  RootType Type;
+  Register Register;
+  union {
+    uint32_t Num32BitConstants;
+    RootDescriptorFlags Flags = RootDescriptorFlags::None;
+  };
+  uint32_t Space = 0;
+  ShaderVisibility Visibility = ShaderVisibility::All;
+};
+
 struct RootElement {
   enum class ElementType {
     RootFlags,
+    RootParameter,
   };
 
   ElementType Tag;
   union {
     RootFlags Flags;
+    RootParameter Parameter;
   };
 
   // Constructors
   RootElement(RootFlags Flags) : Tag(ElementType::RootFlags), Flags(Flags) {}
+  RootElement(RootParameter Parameter)
+      : Tag(ElementType::RootParameter), Parameter(Parameter) {}
 };
 
 } // namespace root_signature



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