microsoft · Nielsbishere · Sep 4, 2025 · Sep 4, 2025 · Nov 4, 2025 · Nov 4, 2025
diff --git a/docs/ReleaseNotes.md b/docs/ReleaseNotes.md
@@ -23,6 +23,7 @@ The included licenses apply to the following files:
 - Fixed regression: [#7508](https://github.com/microsoft/DirectXShaderCompiler/issues/7508) crash when calling `Load` with `status`.
 - Header file `dxcpix.h` was added to the release package.
 - Moved Linear Algebra (Cooperative Vector) DXIL Opcodes to experimental Shader Model 6.10
+- Added `-fhlsl-unused-resource-bindings=<value>` an option to allow deciding on how to treat unused resource bindings in DXIL; `strip` (default) or `keep-all`. `strip` will strip unused resources before generating bindings for resources without a `: register`, and `keep-all` will keep them around even for reflection (while marking them with D3D_SIF_UNUSED). See [explanation](https://github.com/microsoft/DirectXShaderCompiler/pull/7643#issuecomment-3496917202) for more details.
 
 ### Version 1.8.2505
 

diff --git a/include/dxc/DXIL/DxilConstants.h b/include/dxc/DXIL/DxilConstants.h
@@ -15,6 +15,12 @@
 
 namespace hlsl {
 
+enum class UnusedResourceBinding : uint32_t { Strip, Reserved, KeepAll, Count };
+
+static_assert(UnusedResourceBinding::Count <= UnusedResourceBinding(7),
+              "Only 3 bits are reserved for UnusedResourceBinding by HLOptions "
+              "and ShaderFlags");
+
 /* <py>
 import hctdb_instrhelp
 </py> */

diff --git a/include/dxc/DXIL/DxilModule.h b/include/dxc/DXIL/DxilModule.h
@@ -112,8 +112,10 @@ class DxilModule {
   const std::vector<std::unique_ptr<DxilResource>> &GetUAVs() const;
 
   void RemoveUnusedResources();
-  void RemoveResourcesWithUnusedSymbols();
+  bool RemoveResourcesWithUnusedSymbols();
+  bool RemoveEmptyBuffers();
   void RemoveFunction(llvm::Function *F);
+  bool MarkUnusedResources();
 
   bool RenameResourcesWithPrefix(const std::string &prefix);
   bool RenameResourceGlobalsWithBinding(bool bKeepName = true);
@@ -287,6 +289,9 @@ class DxilModule {
   // Intermediate options that do not make it to DXIL
   void SetLegacyResourceReservation(bool legacyResourceReservation);
   bool GetLegacyResourceReservation() const;
+
+  void SetUnusedResourceBinding(UnusedResourceBinding unusedResourceBinding);
+  UnusedResourceBinding GetUnusedResourceBinding() const;
   void ClearIntermediateOptions();
 
   // Hull and Domain shaders.
@@ -344,9 +349,7 @@ class DxilModule {
       DXIL::PrimitiveTopology::Undefined;
   unsigned m_ActiveStreamMask = 0;
 
-  enum IntermediateFlags : uint32_t {
-    LegacyResourceReservation = 1 << 0,
-  };
+  enum IntermediateFlags : uint32_t { LegacyResourceReservation = 1 << 0 };
 
   llvm::LLVMContext &m_Ctx;
   llvm::Module *m_pModule = nullptr;
@@ -383,6 +386,7 @@ class DxilModule {
   bool m_bUseMinPrecision = true; // use min precision by default;
   bool m_bAllResourcesBound = false;
   bool m_bResMayAlias = false;
+  UnusedResourceBinding m_unusedResourceBinding = UnusedResourceBinding::Strip;
 
   // properties from HLModule that should not make it to the final DXIL
   uint32_t m_IntermediateFlags = 0;

diff --git a/include/dxc/DXIL/DxilResourceBase.h b/include/dxc/DXIL/DxilResourceBase.h
@@ -46,6 +46,7 @@ class DxilResourceBase {
   llvm::Value *GetHandle() const;
   bool IsAllocated() const;
   bool IsUnbounded() const;
+  bool IsUnused() const;
 
   void SetKind(DxilResourceBase::Kind ResourceKind);
   void SetSpaceID(unsigned SpaceID);
@@ -55,6 +56,7 @@ class DxilResourceBase {
   void SetGlobalName(const std::string &Name);
   void SetHandle(llvm::Value *pHandle);
   void SetHLSLType(llvm::Type *Ty);
+  void SetIsUnused(bool IsUnused);
 
   // TODO: check whether we can make this a protected method.
   void SetID(unsigned ID);
@@ -75,6 +77,7 @@ class DxilResourceBase {
   unsigned m_SpaceID;        // Root signature space.
   unsigned m_LowerBound;     // Range lower bound.
   unsigned m_RangeSize;      // Range size in entries.
+  bool m_IsUnused;
   llvm::Constant *m_pSymbol; // Global variable.
   std::string m_Name;        // Unmangled name of the global variable.
   llvm::Value

diff --git a/include/dxc/DXIL/DxilShaderFlags.h b/include/dxc/DXIL/DxilShaderFlags.h
@@ -16,6 +16,7 @@
 namespace hlsl {
 class DxilModule;
 struct DxilFunctionProps;
+enum class UnusedResourceBinding : uint32_t;
 }
 
 namespace llvm {
@@ -219,6 +220,14 @@ class ShaderFlags {
   void SetRequiresGroup(bool flag) { m_bRequiresGroup = flag; }
   bool GetRequiresGroup() const { return m_bRequiresGroup; }
 
+  void SetUnusedResourceBinding(UnusedResourceBinding bindings) {
+    m_UnusedResourceBinding = unsigned(bindings);
+  }
+
+  UnusedResourceBinding GetUnusedResourceBinding() {
+    return UnusedResourceBinding(m_UnusedResourceBinding);
+  }
+
 private:
   // Bit: 0
   unsigned
@@ -359,7 +368,9 @@ class ShaderFlags {
   unsigned m_bRequiresGroup : 1; // SHADER_FEATURE_OPT_REQUIRES_GROUP
                                  // (OptFeatureInfo_RequiresGroup)
 
-  uint32_t m_align1 : 23; // align to 64 bit.
+  unsigned m_UnusedResourceBinding : 3;
+
+  uint32_t m_align1 : 20; // align to 64 bit.
 };
 
 } // namespace hlsl
diff --git a/include/dxc/HLSL/HLModule.h b/include/dxc/HLSL/HLModule.h
@@ -54,7 +54,7 @@ struct HLOptions {
         bDisableOptimizations(false), PackingStrategy(0),
         bUseMinPrecision(false), bDX9CompatMode(false), bFXCCompatMode(false),
         bLegacyResourceReservation(false), bForceZeroStoreLifetimes(false),
-        unused(0) {}
+        bUnusedResourceBinding(0), unused(0) {}
   uint32_t GetHLOptionsRaw() const;
   void SetHLOptionsRaw(uint32_t data);
   unsigned bDefaultRowMajor : 1;
@@ -70,7 +70,8 @@ struct HLOptions {
   unsigned bLegacyResourceReservation : 1;
   unsigned bForceZeroStoreLifetimes : 1;
   unsigned bResMayAlias : 1;
-  unsigned unused : 19;
+  unsigned bUnusedResourceBinding : 3;
+  unsigned unused : 17;
 };
 
 typedef std::unordered_map<const llvm::Function *,

diff --git a/include/dxc/Support/HLSLOptions.h b/include/dxc/Support/HLSLOptions.h
@@ -21,6 +21,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Option/ArgList.h"
 
+#include "dxc/DXIL/DxilConstants.h"
 #include "dxc/Support/WinIncludes.h"
 
 #include "dxc/dxcapi.h"
@@ -227,7 +228,9 @@ class DxcOpts {
   std::string TimeTrace = "";           // OPT_ftime_trace[EQ]
   unsigned TimeTraceGranularity = 500;  // OPT_ftime_trace_granularity_EQ
   bool VerifyDiagnostics = false;       // OPT_verify
-  bool Verbose = false;                 // OPT_verbose
+  UnusedResourceBinding UnusedResourceBinding =
+      UnusedResourceBinding::Strip; // OPT_fhlsl_unused_resource_bindings_EQ
+  bool Verbose = false;             // OPT_verbose
 
   // Optimization pass enables, disables and selects
   OptimizationToggles

diff --git a/include/dxc/Support/HLSLOptions.td b/include/dxc/Support/HLSLOptions.td
@@ -576,6 +576,9 @@ def getprivate : JoinedOrSeparate<["-", "/"], "getprivate">, Flags<[DriverOption
 def nologo : Flag<["-", "/"], "nologo">, Group<hlslcore_Group>, Flags<[DriverOption, HelpHidden]>,
   HelpText<"Suppress copyright message">;
 
+def fhlsl_unused_resource_bindings_EQ : Joined<["-"], "fhlsl-unused-resource-bindings=">, Group<hlslcomp_Group>, Flags<[CoreOption]>,
+  HelpText<"Control handling of unused resource bindings:\n\t\t\t'strip' (default, unused resources are stripped and their binding slots are freed up).\n\t\t\t'keep-all' (keep all unused resources around but mark them with D3D_SIF_UNUSED for reflection).">;
+
 //////////////////////////////////////////////////////////////////////////////
 // Rewriter Options
 

diff --git a/lib/DXIL/DxilMetadataHelper.cpp b/lib/DXIL/DxilMetadataHelper.cpp
@@ -693,7 +693,9 @@ void DxilMDHelper::GetDxilResources(const MDOperand &MDO, const MDTuple *&pSRVs,
 
 void DxilMDHelper::EmitDxilResourceBase(const DxilResourceBase &R,
                                         Metadata *ppMDVals[]) {
-  ppMDVals[kDxilResourceBaseID] = Uint32ToConstMD(R.GetID());
+  assert(R.GetID() < (1u << 31) && "R.GetId() out of bounds");
+  uint32_t idAndIsUnused = R.GetID() | (R.IsUnused() ? (1u << 31) : 0);
+  ppMDVals[kDxilResourceBaseID] = Uint32ToConstMD(idAndIsUnused);
   Constant *GlobalSymbol = R.GetGlobalSymbol();
   // For sm66+, global symbol will be mutated into handle type.
   // Save hlsl type by generate bitcast on global symbol.
@@ -722,7 +724,11 @@ void DxilMDHelper::LoadDxilResourceBase(const MDOperand &MDO,
   IFTBOOL(pTupleMD->getNumOperands() >= kDxilResourceBaseNumFields,
           DXC_E_INCORRECT_DXIL_METADATA);
 
-  R.SetID(ConstMDToUint32(pTupleMD->getOperand(kDxilResourceBaseID)));
+  uint32_t idAndIsUnused =
+      ConstMDToUint32(pTupleMD->getOperand(kDxilResourceBaseID));
+
+  R.SetID(idAndIsUnused << 1 >> 1);
+  R.SetIsUnused(idAndIsUnused >> 31);
   Constant *GlobalSymbol = dyn_cast<Constant>(
       ValueMDToValue(pTupleMD->getOperand(kDxilResourceBaseVariable)));
   // For sm66+, global symbol will be mutated into handle type.

diff --git a/lib/DXIL/DxilModule.cpp b/lib/DXIL/DxilModule.cpp
@@ -586,6 +586,15 @@ bool DxilModule::GetLegacyResourceReservation() const {
   return (m_IntermediateFlags & LegacyResourceReservation) != 0;
 }
 
+void DxilModule::SetUnusedResourceBinding(
+    UnusedResourceBinding unusedResourceBinding) {
+  m_unusedResourceBinding = unusedResourceBinding;
+}
+
+UnusedResourceBinding DxilModule::GetUnusedResourceBinding() const {
+  return m_unusedResourceBinding;
+}
+
 void DxilModule::ClearIntermediateOptions() { m_IntermediateFlags = 0; }
 
 unsigned DxilModule::GetInputControlPointCount() const {
@@ -1021,8 +1030,9 @@ void DxilModule::RemoveUnusedResources() {
 
 namespace {
 template <typename TResource>
-static void RemoveResourcesWithUnusedSymbolsHelper(
+static bool RemoveResourcesWithUnusedSymbolsHelper(
     std::vector<std::unique_ptr<TResource>> &vec) {
+  bool modif = false;
   unsigned resID = 0;
   std::unordered_set<GlobalVariable *>
       eraseList; // Need in case of duplicate defs of lib resources
@@ -1031,6 +1041,7 @@ static void RemoveResourcesWithUnusedSymbolsHelper(
     Constant *symbol = (*c)->GetGlobalSymbol();
     symbol->removeDeadConstantUsers();
     if (symbol->user_empty()) {
+      modif = true;
       p = vec.erase(c);
       if (GlobalVariable *GV = dyn_cast<GlobalVariable>(symbol))
         eraseList.insert(GV);
@@ -1044,14 +1055,80 @@ static void RemoveResourcesWithUnusedSymbolsHelper(
   for (auto gv : eraseList) {
     gv->eraseFromParent();
   }
+  return modif;
+}
+} // namespace
+
+bool DxilModule::RemoveResourcesWithUnusedSymbols() {
+  bool modif = false;
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_SRVs);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_UAVs);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_CBuffers);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_Samplers);
+  return modif;
+}
+
+bool DxilModule::RemoveEmptyBuffers() {
+
+  bool mod = false;
+  unsigned resID = 0;
+  std::unordered_set<GlobalVariable *>
+      eraseList; // Need in case of duplicate defs of lib resources
+
+  for (auto p = m_CBuffers.begin(); p != m_CBuffers.end();) {
+
+    auto c = p++;
+
+    Constant *symbol = (*c)->GetGlobalSymbol();
+
+    if (!c->get()->GetSize()) {
+      p = m_CBuffers.erase(c);
+      if (GlobalVariable *GV = dyn_cast<GlobalVariable>(symbol))
+        eraseList.insert(GV);
+      mod = true;
+      continue;
+    }
+
+    if ((*c)->GetID() != resID)
+      (*c)->SetID(resID);
+
+    resID++;
+  }
+
+  for (auto gv : eraseList)
+    gv->eraseFromParent();
+
+  return mod;
+}
+
+namespace {
+template <typename TResource>
+static bool MarkResourcesUnused(std::vector<std::unique_ptr<TResource>> &vec) {
+
+  bool modif = false;
+
+  for (auto p = vec.begin(); p != vec.end();) {
+    auto c = p++;
+    Constant *symbol = (*c)->GetGlobalSymbol();
+    symbol->removeDeadConstantUsers();
+    if (symbol->user_empty()) {
+      (*c)->SetIsUnused(true);
+      modif = true;
+      continue;
+    }
+  }
+
+  return modif;
 }
 } // namespace
 
-void DxilModule::RemoveResourcesWithUnusedSymbols() {
-  RemoveResourcesWithUnusedSymbolsHelper(m_SRVs);
-  RemoveResourcesWithUnusedSymbolsHelper(m_UAVs);
-  RemoveResourcesWithUnusedSymbolsHelper(m_CBuffers);
-  RemoveResourcesWithUnusedSymbolsHelper(m_Samplers);
+bool DxilModule::MarkUnusedResources() {
+  bool modif = true;
+  modif |= MarkResourcesUnused(m_SRVs);
+  modif |= MarkResourcesUnused(m_UAVs);
+  modif |= MarkResourcesUnused(m_CBuffers);
+  modif |= MarkResourcesUnused(m_Samplers);
+  return modif;
 }
 
 namespace {
@@ -1533,6 +1610,7 @@ void DxilModule::LoadDxilMetadata() {
     m_bUseMinPrecision = !m_ShaderFlags.GetUseNativeLowPrecision();
     m_bDisableOptimizations = m_ShaderFlags.GetDisableOptimizations();
     m_bAllResourcesBound = m_ShaderFlags.GetAllResourcesBound();
+    m_unusedResourceBinding = m_ShaderFlags.GetUnusedResourceBinding();
     m_bResMayAlias = !m_ShaderFlags.GetResMayNotAlias();
   }
 

diff --git a/lib/DXIL/DxilResourceBase.cpp b/lib/DXIL/DxilResourceBase.cpp
@@ -20,7 +20,7 @@ namespace hlsl {
 DxilResourceBase::DxilResourceBase(Class C)
     : m_Class(C), m_Kind(Kind::Invalid), m_ID(UINT_MAX), m_SpaceID(0),
       m_LowerBound(0), m_RangeSize(0), m_pSymbol(nullptr), m_pHandle(nullptr),
-      m_pHLSLTy(nullptr) {}
+      m_pHLSLTy(nullptr), m_IsUnused(false) {}
 
 DxilResourceBase::Class DxilResourceBase::GetClass() const { return m_Class; }
 DxilResourceBase::Kind DxilResourceBase::GetKind() const { return m_Kind; }
@@ -48,6 +48,7 @@ llvm::Type *DxilResourceBase::GetHLSLType() const {
 }
 bool DxilResourceBase::IsAllocated() const { return m_LowerBound != UINT_MAX; }
 bool DxilResourceBase::IsUnbounded() const { return m_RangeSize == UINT_MAX; }
+bool DxilResourceBase::IsUnused() const { return m_IsUnused; }
 
 void DxilResourceBase::SetClass(Class C) { m_Class = C; }
 void DxilResourceBase::SetID(unsigned ID) { m_ID = ID; }
@@ -56,6 +57,7 @@ void DxilResourceBase::SetLowerBound(unsigned LB) { m_LowerBound = LB; }
 void DxilResourceBase::SetRangeSize(unsigned RangeSize) {
   m_RangeSize = RangeSize;
 }
+void DxilResourceBase::SetIsUnused(bool IsUnused) { m_IsUnused = IsUnused; }
 void DxilResourceBase::SetGlobalSymbol(llvm::Constant *pGV) { m_pSymbol = pGV; }
 void DxilResourceBase::SetGlobalName(const std::string &Name) { m_Name = Name; }
 void DxilResourceBase::SetHandle(llvm::Value *pHandle) { m_pHandle = pHandle; }

diff --git a/lib/DXIL/DxilShaderFlags.cpp b/lib/DXIL/DxilShaderFlags.cpp
@@ -47,7 +47,7 @@ ShaderFlags::ShaderFlags()
       m_bAdvancedTextureOps(false), m_bWriteableMSAATextures(false),
       m_bReserved(false), m_bSampleCmpGradientOrBias(false),
       m_bExtendedCommandInfo(false), m_bUsesDerivatives(false),
-      m_bRequiresGroup(false), m_align1(0) {
+      m_bRequiresGroup(false), m_UnusedResourceBinding(0), m_align1(0) {
   // Silence unused field warnings
   (void)m_align1;
 }
@@ -412,6 +412,7 @@ ShaderFlags ShaderFlags::CollectShaderFlags(const Function *F,
   flag.SetUseNativeLowPrecision(!M->GetUseMinPrecision());
   flag.SetDisableOptimizations(M->GetDisableOptimization());
   flag.SetAllResourcesBound(M->GetAllResourcesBound());
+  flag.SetUnusedResourceBinding(M->GetUnusedResourceBinding());
 
   bool hasDouble = false;
   // ddiv dfma drcp d2i d2u i2d u2d.

diff --git a/lib/DxcSupport/HLSLOptions.cpp b/lib/DxcSupport/HLSLOptions.cpp
@@ -865,6 +865,21 @@ int ReadDxcOpts(const OptTable *optionTable, unsigned flagsToInclude,
   opts.TimeReport = Args.hasFlag(OPT_ftime_report, OPT_INVALID, false);
   opts.TimeTrace = Args.hasFlag(OPT_ftime_trace, OPT_INVALID, false) ? "-" : "";
   opts.VerifyDiagnostics = Args.hasFlag(OPT_verify, OPT_INVALID, false);
+
+  std::string UnusedResources =
+      Args.getLastArgValue(OPT_fhlsl_unused_resource_bindings_EQ, "strip");
+
+  if (UnusedResources == "strip")
+    opts.UnusedResourceBinding = UnusedResourceBinding::Strip;
+  else if (UnusedResources == "keep-all")
+    opts.UnusedResourceBinding = UnusedResourceBinding::KeepAll;
+  else {
+    errors << "Error: Invalid value for -fhlsl-unused-resource-bindings option "
+              "specified ("
+           << UnusedResources << "). Must be one of: strip, keep-all";
+    return 1;
+  }
+
   opts.Verbose = Args.hasFlag(OPT_verbose, OPT_INVALID, false);
   if (Args.hasArg(OPT_ftime_trace_EQ))
     opts.TimeTrace = Args.getLastArgValue(OPT_ftime_trace_EQ);