llvm · inbelic · Aug 27, 2025 · Aug 26, 2025 · Aug 26, 2025 · Aug 26, 2025
diff --git a/llvm/include/llvm/MC/DXContainerRootSignature.h b/llvm/include/llvm/MC/DXContainerRootSignature.h
@@ -110,6 +110,8 @@ struct RootSignatureDesc {
   LLVM_ABI void write(raw_ostream &OS) const;
 
   LLVM_ABI size_t getSize() const;
+  LLVM_ABI uint32_t computeRootParametersOffset() const;
+  LLVM_ABI uint32_t computeStaticSamplersOffset() const;
 };
 } // namespace mcdxbc
 } // namespace llvm

diff --git a/llvm/include/llvm/ObjectYAML/DXContainerYAML.h b/llvm/include/llvm/ObjectYAML/DXContainerYAML.h
@@ -187,9 +187,9 @@ struct RootSignatureYamlDesc {
 
   uint32_t Version;
   uint32_t NumRootParameters;
-  uint32_t RootParametersOffset;
+  std::optional<uint32_t> RootParametersOffset;
   uint32_t NumStaticSamplers;
-  uint32_t StaticSamplersOffset;
+  std::optional<uint32_t> StaticSamplersOffset;
 
   RootParameterYamlDesc Parameters;
   SmallVector<StaticSamplerYamlDesc> StaticSamplers;

diff --git a/llvm/lib/MC/DXContainerRootSignature.cpp b/llvm/lib/MC/DXContainerRootSignature.cpp
@@ -20,32 +20,43 @@ static uint32_t writePlaceholder(raw_svector_ostream &Stream) {
   return Offset;
 }
 
-static void rewriteOffsetToCurrentByte(raw_svector_ostream &Stream,
-                                       uint32_t Offset) {
+static uint32_t rewriteOffsetToCurrentByte(raw_svector_ostream &Stream,
+                                           uint32_t Offset) {
   uint32_t Value =
       support::endian::byte_swap<uint32_t, llvm::endianness::little>(
           Stream.tell());
   Stream.pwrite(reinterpret_cast<const char *>(&Value), sizeof(Value), Offset);
+  return Value;
 }
 
 size_t RootSignatureDesc::getSize() const {
-  size_t Size =
-      sizeof(dxbc::RTS0::v1::RootSignatureHeader) +
-      ParametersContainer.size() * sizeof(dxbc::RTS0::v1::RootParameterHeader) +
+  uint32_t StaticSamplersOffset = computeStaticSamplersOffset();
+  size_t StaticSamplersSize =
       StaticSamplers.size() * sizeof(dxbc::RTS0::v1::StaticSampler);
 
+  return size_t(StaticSamplersOffset) + StaticSamplersSize;
+}
+
+uint32_t RootSignatureDesc::computeRootParametersOffset() const {
+  return sizeof(dxbc::RTS0::v1::RootSignatureHeader);
+}
+
+uint32_t RootSignatureDesc::computeStaticSamplersOffset() const {
+  uint32_t Offset = computeRootParametersOffset();
+
   for (const RootParameterInfo &I : ParametersContainer) {
+    Offset += sizeof(dxbc::RTS0::v1::RootParameterHeader);
     switch (I.Type) {
     case dxbc::RootParameterType::Constants32Bit:
-      Size += sizeof(dxbc::RTS0::v1::RootConstants);
+      Offset += sizeof(dxbc::RTS0::v1::RootConstants);
       break;
     case dxbc::RootParameterType::CBV:
     case dxbc::RootParameterType::SRV:
     case dxbc::RootParameterType::UAV:
       if (Version == 1)
-        Size += sizeof(dxbc::RTS0::v1::RootDescriptor);
+        Offset += sizeof(dxbc::RTS0::v1::RootDescriptor);
       else
-        Size += sizeof(dxbc::RTS0::v2::RootDescriptor);
+        Offset += sizeof(dxbc::RTS0::v2::RootDescriptor);
 
       break;
     case dxbc::RootParameterType::DescriptorTable:
@@ -54,15 +65,16 @@ size_t RootSignatureDesc::getSize() const {
 
       // 4 bytes for the number of ranges in table and
       // 4 bytes for the ranges offset
-      Size += 2 * sizeof(uint32_t);
+      Offset += 2 * sizeof(uint32_t);
       if (Version == 1)
-        Size += sizeof(dxbc::RTS0::v1::DescriptorRange) * Table.Ranges.size();
+        Offset += sizeof(dxbc::RTS0::v1::DescriptorRange) * Table.Ranges.size();
       else
-        Size += sizeof(dxbc::RTS0::v2::DescriptorRange) * Table.Ranges.size();
+        Offset += sizeof(dxbc::RTS0::v2::DescriptorRange) * Table.Ranges.size();
       break;
     }
   }
-  return Size;
+
+  return Offset;
 }
 
 void RootSignatureDesc::write(raw_ostream &OS) const {
@@ -76,11 +88,7 @@ void RootSignatureDesc::write(raw_ostream &OS) const {
   support::endian::write(BOS, NumParameters, llvm::endianness::little);
   support::endian::write(BOS, RootParameterOffset, llvm::endianness::little);
   support::endian::write(BOS, NumSamplers, llvm::endianness::little);
-  uint32_t SSO = StaticSamplersOffset;
-  if (NumSamplers > 0)
-    SSO = writePlaceholder(BOS);
-  else
-    support::endian::write(BOS, SSO, llvm::endianness::little);
+  uint32_t SSO = writePlaceholder(BOS);
   support::endian::write(BOS, Flags, llvm::endianness::little);
 
   SmallVector<uint32_t> ParamsOffsets;
@@ -144,23 +152,23 @@ void RootSignatureDesc::write(raw_ostream &OS) const {
     }
     }
   }
-  if (NumSamplers > 0) {
-    rewriteOffsetToCurrentByte(BOS, SSO);
-    for (const auto &S : StaticSamplers) {
-      support::endian::write(BOS, S.Filter, llvm::endianness::little);
-      support::endian::write(BOS, S.AddressU, llvm::endianness::little);
-      support::endian::write(BOS, S.AddressV, llvm::endianness::little);
-      support::endian::write(BOS, S.AddressW, llvm::endianness::little);
-      support::endian::write(BOS, S.MipLODBias, llvm::endianness::little);
-      support::endian::write(BOS, S.MaxAnisotropy, llvm::endianness::little);
-      support::endian::write(BOS, S.ComparisonFunc, llvm::endianness::little);
-      support::endian::write(BOS, S.BorderColor, llvm::endianness::little);
-      support::endian::write(BOS, S.MinLOD, llvm::endianness::little);
-      support::endian::write(BOS, S.MaxLOD, llvm::endianness::little);
-      support::endian::write(BOS, S.ShaderRegister, llvm::endianness::little);
-      support::endian::write(BOS, S.RegisterSpace, llvm::endianness::little);
-      support::endian::write(BOS, S.ShaderVisibility, llvm::endianness::little);
-    }
+  [[maybe_unused]] uint32_t Offset = rewriteOffsetToCurrentByte(BOS, SSO);
+  assert(Offset == computeStaticSamplersOffset() &&
+         "Computed offset does not match written offset");
+  for (const auto &S : StaticSamplers) {
+    support::endian::write(BOS, S.Filter, llvm::endianness::little);
+    support::endian::write(BOS, S.AddressU, llvm::endianness::little);
+    support::endian::write(BOS, S.AddressV, llvm::endianness::little);
+    support::endian::write(BOS, S.AddressW, llvm::endianness::little);
+    support::endian::write(BOS, S.MipLODBias, llvm::endianness::little);
+    support::endian::write(BOS, S.MaxAnisotropy, llvm::endianness::little);
+    support::endian::write(BOS, S.ComparisonFunc, llvm::endianness::little);
+    support::endian::write(BOS, S.BorderColor, llvm::endianness::little);
+    support::endian::write(BOS, S.MinLOD, llvm::endianness::little);
+    support::endian::write(BOS, S.MaxLOD, llvm::endianness::little);
+    support::endian::write(BOS, S.ShaderRegister, llvm::endianness::little);
+    support::endian::write(BOS, S.RegisterSpace, llvm::endianness::little);
+    support::endian::write(BOS, S.ShaderVisibility, llvm::endianness::little);
   }
   assert(Storage.size() == getSize());
   OS.write(Storage.data(), Storage.size());

diff --git a/llvm/lib/ObjectYAML/DXContainerEmitter.cpp b/llvm/lib/ObjectYAML/DXContainerEmitter.cpp
@@ -38,7 +38,7 @@ class DXContainerWriter {
   Error validateSize(uint32_t Computed);
 
   void writeHeader(raw_ostream &OS);
-  void writeParts(raw_ostream &OS);
+  Error writeParts(raw_ostream &OS);
 };
 } // namespace
 
@@ -107,7 +107,7 @@ void DXContainerWriter::writeHeader(raw_ostream &OS) {
            Offsets.size() * sizeof(uint32_t));
 }
 
-void DXContainerWriter::writeParts(raw_ostream &OS) {
+Error DXContainerWriter::writeParts(raw_ostream &OS) {
   uint32_t RollingOffset =
       sizeof(dxbc::Header) + (ObjectFile.Header.PartCount * sizeof(uint32_t));
   for (auto I : llvm::zip(ObjectFile.Parts, *ObjectFile.Header.PartOffsets)) {
@@ -269,9 +269,7 @@ void DXContainerWriter::writeParts(raw_ostream &OS) {
       mcdxbc::RootSignatureDesc RS;
       RS.Flags = P.RootSignature->getEncodedFlags();
       RS.Version = P.RootSignature->Version;
-      RS.RootParameterOffset = P.RootSignature->RootParametersOffset;
       RS.NumStaticSamplers = P.RootSignature->NumStaticSamplers;
-      RS.StaticSamplersOffset = P.RootSignature->StaticSamplersOffset;
 
       for (DXContainerYAML::RootParameterLocationYaml &L :
            P.RootSignature->Parameters.Locations) {
@@ -323,8 +321,10 @@ void DXContainerWriter::writeParts(raw_ostream &OS) {
             Range.RegisterSpace = R.RegisterSpace;
             Range.OffsetInDescriptorsFromTableStart =
                 R.OffsetInDescriptorsFromTableStart;
+
             if (RS.Version > 1)
               Range.Flags = R.getEncodedFlags();
+
             Table.Ranges.push_back(Range);
           }
           RS.ParametersContainer.addParameter(Type, Visibility, Table);
@@ -352,6 +352,27 @@ void DXContainerWriter::writeParts(raw_ostream &OS) {
         RS.StaticSamplers.push_back(NewSampler);
       }
 
+      // Handling of offsets
+      RS.RootParameterOffset = RS.computeRootParametersOffset();
+      if (P.RootSignature->RootParametersOffset &&
+          P.RootSignature->RootParametersOffset.value() !=
+              RS.RootParameterOffset) {
+        return createStringError(
+            errc::invalid_argument,
+            "Specified RootParametersOffset does not match required value: %d.",
+            RS.RootParameterOffset);
+      }
+
+      RS.StaticSamplersOffset = RS.computeStaticSamplersOffset();
+      if (P.RootSignature->StaticSamplersOffset &&
+          P.RootSignature->StaticSamplersOffset.value() !=
+              RS.StaticSamplersOffset) {
+        return createStringError(
+            errc::invalid_argument,
+            "Specified StaticSamplersOffset does not match computed value: %d.",
+            RS.StaticSamplersOffset);
+      }
+
       RS.write(OS);
       break;
     }
@@ -361,14 +382,15 @@ void DXContainerWriter::writeParts(raw_ostream &OS) {
       OS.write_zeros(PartSize - BytesWritten);
     RollingOffset += PartSize;
   }
+
+  return Error::success();
 }
 
 Error DXContainerWriter::write(raw_ostream &OS) {
   if (Error Err = computePartOffsets())
     return Err;
   writeHeader(OS);
-  writeParts(OS);
-  return Error::success();
+  return writeParts(OS);
 }
 
 namespace llvm {

diff --git a/llvm/lib/ObjectYAML/DXContainerYAML.cpp b/llvm/lib/ObjectYAML/DXContainerYAML.cpp
@@ -376,9 +376,9 @@ void MappingTraits<DXContainerYAML::RootSignatureYamlDesc>::mapping(
     IO &IO, DXContainerYAML::RootSignatureYamlDesc &S) {
   IO.mapRequired("Version", S.Version);
   IO.mapRequired("NumRootParameters", S.NumRootParameters);
-  IO.mapRequired("RootParametersOffset", S.RootParametersOffset);
+  IO.mapOptional("RootParametersOffset", S.RootParametersOffset, std::nullopt);
   IO.mapRequired("NumStaticSamplers", S.NumStaticSamplers);
-  IO.mapRequired("StaticSamplersOffset", S.StaticSamplersOffset);
+  IO.mapOptional("StaticSamplersOffset", S.StaticSamplersOffset, std::nullopt);
   IO.mapRequired("Parameters", S.Parameters.Locations, S);
   IO.mapOptional("Samplers", S.StaticSamplers);
 #define ROOT_SIGNATURE_FLAG(Num, Val) IO.mapOptional(#Val, S.Val, false);

diff --git a/...t/CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable-AllValidFlagCombinations.ll b/...t/CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable-AllValidFlagCombinations.ll
@@ -59,7 +59,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ;DXC-NEXT:      NumRootParameters: 1
 ;DXC-NEXT:      RootParametersOffset: 24
 ;DXC-NEXT:      NumStaticSamplers: 0
-;DXC-NEXT:      StaticSamplersOffset: 0
+;DXC-NEXT:      StaticSamplersOffset: 380
 ;DXC-NEXT:      Parameters:
 ;DXC-NEXT:        - ParameterType:   0
 ;DXC-NEXT:          ShaderVisibility: 0

diff --git a/...CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable-AllValidFlagCombinationsV1.ll b/...CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable-AllValidFlagCombinationsV1.ll
@@ -24,7 +24,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:       NumRootParameters: 1
 ; DXC-NEXT:       RootParametersOffset: 24
 ; DXC-NEXT:       NumStaticSamplers: 0
-; DXC-NEXT:       StaticSamplersOffset: 0
+; DXC-NEXT:       StaticSamplersOffset: 84
 ; DXC-NEXT:       Parameters:
 ; DXC-NEXT:         - ParameterType:   0
 ; DXC-NEXT:           ShaderVisibility: 0

diff --git a/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable.ll b/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable.ll
@@ -26,7 +26,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:      NumRootParameters: 1 
 ; DXC-NEXT:      RootParametersOffset: 24 
 ; DXC-NEXT:      NumStaticSamplers: 0
-; DXC-NEXT:      StaticSamplersOffset: 0
+; DXC-NEXT:      StaticSamplersOffset: 92
 ; DXC-NEXT:      Parameters:
 ; DXC-NEXT:        - ParameterType:   0
 ; DXC-NEXT:          ShaderVisibility: 0

diff --git a/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-Flags.ll b/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-Flags.ll
@@ -25,6 +25,6 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:      NumRootParameters: 0
 ; DXC-NEXT:      RootParametersOffset: 24
 ; DXC-NEXT:      NumStaticSamplers: 0
-; DXC-NEXT:      StaticSamplersOffset: 0
+; DXC-NEXT:      StaticSamplersOffset: 24
 ; DXC-NEXT:      Parameters: []
 ; DXC-NEXT:      AllowInputAssemblerInputLayout: true
diff --git a/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootConstants.ll b/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootConstants.ll
@@ -24,7 +24,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:      NumRootParameters: 1 
 ; DXC-NEXT:      RootParametersOffset: 24 
 ; DXC-NEXT:      NumStaticSamplers: 0
-; DXC-NEXT:      StaticSamplersOffset: 0
+; DXC-NEXT:      StaticSamplersOffset: 48
 ; DXC-NEXT:      Parameters:
 ; DXC-NEXT:        - ParameterType:   1
 ; DXC-NEXT:          ShaderVisibility: 0

diff --git a/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootDescriptor.ll b/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootDescriptor.ll
@@ -24,7 +24,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:      NumRootParameters: 1 
 ; DXC-NEXT:      RootParametersOffset: 24 
 ; DXC-NEXT:      NumStaticSamplers: 0
-; DXC-NEXT:      StaticSamplersOffset: 0
+; DXC-NEXT:      StaticSamplersOffset: 48
 ; DXC-NEXT:      Parameters:
 ; DXC-NEXT:        - ParameterType:   2
 ; DXC-NEXT:          ShaderVisibility: 0

diff --git a/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootDescriptor_V1.ll b/llvm/test/CodeGen/DirectX/ContainerData/RootSignature-RootDescriptor_V1.ll
@@ -24,7 +24,7 @@ attributes #0 = { "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" }
 ; DXC-NEXT:      NumRootParameters: 1 
 ; DXC-NEXT:      RootParametersOffset: 24 
 ; DXC-NEXT:      NumStaticSamplers: 0
-; DXC-NEXT:      StaticSamplersOffset: 0
+; DXC-NEXT:      StaticSamplersOffset: 44
 ; DXC-NEXT:      Parameters:
 ; DXC-NEXT:        - ParameterType:   2
 ; DXC-NEXT:          ShaderVisibility: 0

diff --git a/llvm/test/ObjectYAML/DXContainer/RootSignature-Descriptor1.0.yaml b/llvm/test/ObjectYAML/DXContainer/RootSignature-Descriptor1.0.yaml
@@ -17,7 +17,7 @@ Parts:
       NumRootParameters: 1
       RootParametersOffset: 24
       NumStaticSamplers: 0
-      StaticSamplersOffset: 60
+      StaticSamplersOffset: 44
       Parameters:         
       - ParameterType: 2 # SRV
         ShaderVisibility: 3 # Domain
@@ -34,7 +34,7 @@ Parts:
 # CHECK-NEXT:      NumRootParameters: 1
 # CHECK-NEXT:      RootParametersOffset: 24
 # CHECK-NEXT:      NumStaticSamplers: 0
-# CHECK-NEXT:      StaticSamplersOffset: 60
+# CHECK-NEXT:      StaticSamplersOffset: 44
 # CHECK-NEXT:      Parameters:         
 # CHECK-NEXT:      - ParameterType: 2
 # CHECK-NEXT:        ShaderVisibility: 3

diff --git a/llvm/test/ObjectYAML/DXContainer/RootSignature-Descriptor1.1.yaml b/llvm/test/ObjectYAML/DXContainer/RootSignature-Descriptor1.1.yaml
@@ -17,7 +17,7 @@ Parts:
       NumRootParameters: 1
       RootParametersOffset: 24
       NumStaticSamplers: 0
-      StaticSamplersOffset: 60
+      StaticSamplersOffset: 48
       Parameters:         
       - ParameterType: 2 # SRV
         ShaderVisibility: 3 # Domain
@@ -35,7 +35,7 @@ Parts:
 # CHECK-NEXT:      NumRootParameters: 1
 # CHECK-NEXT:      RootParametersOffset: 24
 # CHECK-NEXT:      NumStaticSamplers: 0
-# CHECK-NEXT:      StaticSamplersOffset: 60
+# CHECK-NEXT:      StaticSamplersOffset: 48
 # CHECK-NEXT:      Parameters:         
 # CHECK-NEXT:      - ParameterType: 2
 # CHECK-NEXT:        ShaderVisibility: 3

diff --git a/llvm/test/ObjectYAML/DXContainer/RootSignature-DescriptorTable1.0.yaml b/llvm/test/ObjectYAML/DXContainer/RootSignature-DescriptorTable1.0.yaml
@@ -18,7 +18,7 @@ Parts:
     NumRootParameters: 1
     RootParametersOffset: 24
     NumStaticSamplers: 0
-    StaticSamplersOffset: 60
+    StaticSamplersOffset: 64
     Parameters:         
     - ParameterType: 0 # SRV
       ShaderVisibility: 3 # Domain
@@ -40,7 +40,7 @@ Parts:
 # CHECK-NEXT:     NumRootParameters: 1
 # CHECK-NEXT:     RootParametersOffset: 24
 # CHECK-NEXT:     NumStaticSamplers: 0
-# CHECK-NEXT:     StaticSamplersOffset: 60
+# CHECK-NEXT:     StaticSamplersOffset: 64
 # CHECK-NEXT:     Parameters:         
 # CHECK-NEXT:     - ParameterType: 0
 # CHECK-NEXT:       ShaderVisibility: 3

diff --git a/llvm/test/ObjectYAML/DXContainer/RootSignature-DescriptorTable1.1.yaml b/llvm/test/ObjectYAML/DXContainer/RootSignature-DescriptorTable1.1.yaml
@@ -18,7 +18,7 @@ Parts:
     NumRootParameters: 1
     RootParametersOffset: 24
     NumStaticSamplers: 0
-    StaticSamplersOffset: 60
+    StaticSamplersOffset: 68
     Parameters:         
     - ParameterType: 0 # SRV
       ShaderVisibility: 3 # Domain
@@ -41,7 +41,7 @@ Parts:
 # CHECK-NEXT:       NumRootParameters: 1
 # CHECK-NEXT:       RootParametersOffset: 24
 # CHECK-NEXT:       NumStaticSamplers: 0
-# CHECK-NEXT:       StaticSamplersOffset: 60
+# CHECK-NEXT:       StaticSamplersOffset: 68
 # CHECK-NEXT:       Parameters:
 # CHECK-NEXT:         - ParameterType:   0
 # CHECK-NEXT:           ShaderVisibility: 3

diff --git a/llvm/test/ObjectYAML/DXContainer/RootSignature-Flags.yaml b/llvm/test/ObjectYAML/DXContainer/RootSignature-Flags.yaml
@@ -17,7 +17,7 @@ Parts:
       NumRootParameters: 0
       RootParametersOffset: 24
       NumStaticSamplers: 0
-      StaticSamplersOffset: 60
+      StaticSamplersOffset: 24
       Parameters: []
       AllowInputAssemblerInputLayout: true
       DenyGeometryShaderRootAccess: true
@@ -29,7 +29,7 @@ Parts:
 # CHECK-NEXT:      NumRootParameters: 0
 # CHECK-NEXT:      RootParametersOffset: 24
 # CHECK-NEXT:      NumStaticSamplers: 0
-# CHECK-NEXT:      StaticSamplersOffset: 60
+# CHECK-NEXT:      StaticSamplersOffset: 24
 # CHECK-NEXT:      Parameters: []
 # CHECK-NEXT:      AllowInputAssemblerInputLayout: true
 # CHECK-NEXT:      DenyGeometryShaderRootAccess: true