microsoft · Nielsbishere · Jul 14, 2025 · Jul 15, 2025 · Jul 15, 2025 · Jul 16, 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 `reserve-all`. `strip` will strip unused resources before generating bindings for resources without a `: register`, and `reserve-all` will keep them reserved for generated bindings while stripping them afterwards. 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, ReserveAll, 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
@@ -112,7 +112,7 @@ class DxilModule {
   const std::vector<std::unique_ptr<DxilResource>> &GetUAVs() const;
 
   void RemoveUnusedResources();
-  void RemoveResourcesWithUnusedSymbols();
+  bool RemoveResourcesWithUnusedSymbols();
   void RemoveFunction(llvm::Function *F);
 
   bool RenameResourcesWithPrefix(const std::string &prefix);
@@ -287,6 +287,9 @@ 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 +347,7 @@ 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 +384,7 @@ 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/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'reserve-all' (do not use binding slots of unused resources when assigning bindings).">;
+
 //////////////////////////////////////////////////////////////////////////////
 // Rewriter Options
 

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
@@ -1034,6 +1044,7 @@ static void RemoveResourcesWithUnusedSymbolsHelper(
       p = vec.erase(c);
       if (GlobalVariable *GV = dyn_cast<GlobalVariable>(symbol))
         eraseList.insert(GV);
+      modif = true;
       continue;
     }
     if ((*c)->GetID() != resID) {
@@ -1044,14 +1055,17 @@ static void RemoveResourcesWithUnusedSymbolsHelper(
   for (auto gv : eraseList) {
     gv->eraseFromParent();
   }
+  return modif;
 }
 } // namespace
 
-void DxilModule::RemoveResourcesWithUnusedSymbols() {
-  RemoveResourcesWithUnusedSymbolsHelper(m_SRVs);
-  RemoveResourcesWithUnusedSymbolsHelper(m_UAVs);
-  RemoveResourcesWithUnusedSymbolsHelper(m_CBuffers);
-  RemoveResourcesWithUnusedSymbolsHelper(m_Samplers);
+bool DxilModule::RemoveResourcesWithUnusedSymbols() {
+  bool modif = false;
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_SRVs);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_UAVs);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_CBuffers);
+  modif |= RemoveResourcesWithUnusedSymbolsHelper(m_Samplers);
+  return modif;
 }
 
 namespace {
@@ -1533,6 +1547,7 @@ 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/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 == "reserve-all")
+    opts.UnusedResourceBinding = UnusedResourceBinding::ReserveAll;
+  else {
+    errors << "Error: Invalid value for -fhlsl-unused-resource-bindings option "
+              "specified ("
+           << UnusedResources << "). Must be one of: strip, reserve-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);

diff --git a/lib/HLSL/DxilCondenseResources.cpp b/lib/HLSL/DxilCondenseResources.cpp
@@ -550,27 +550,31 @@ class DxilLowerCreateHandleForLib : public ModulePass {
     ResourceRegisterAllocator.GatherReservedRegisters(DM);
 
     // Remove unused resources.
-    DM.RemoveResourcesWithUnusedSymbols();
+    if (DM.GetUnusedResourceBinding() == UnusedResourceBinding::Strip)
+      bChanged |= DM.RemoveResourcesWithUnusedSymbols();
 
     unsigned newResources = DM.GetCBuffers().size() + DM.GetUAVs().size() +
                             DM.GetSRVs().size() + DM.GetSamplers().size();
-    bChanged = bChanged || (numResources != newResources);
 
     if (0 == newResources)
       return bChanged;
 
     {
       DxilValueCache *DVC = &getAnalysis<DxilValueCache>();
       bool bLocalChanged = LegalizeResources(M, DVC);
-      if (bLocalChanged) {
+      if (bLocalChanged &&
+          DM.GetUnusedResourceBinding() == UnusedResourceBinding::Strip) {
         // Remove unused resources.
-        DM.RemoveResourcesWithUnusedSymbols();
+        bChanged |= DM.RemoveResourcesWithUnusedSymbols();
       }
       bChanged |= bLocalChanged;
     }
 
     bChanged |= ResourceRegisterAllocator.AllocateRegisters(DM);
 
+    if (DM.GetUnusedResourceBinding() == UnusedResourceBinding::ReserveAll)
+      bChanged |= DM.RemoveResourcesWithUnusedSymbols();
+
     // Fill in top-level CBuffer variable usage bit
     UpdateCBufferUsage();
 

diff --git a/lib/HLSL/DxilGenerationPass.cpp b/lib/HLSL/DxilGenerationPass.cpp
@@ -155,6 +155,8 @@ void InitDxilModuleFromHLModule(HLModule &H, DxilModule &M, bool HasDebugInfo) {
   // bool m_bDisableOptimizations;
   M.SetDisableOptimization(H.GetHLOptions().bDisableOptimizations);
   M.SetLegacyResourceReservation(H.GetHLOptions().bLegacyResourceReservation);
+  M.SetUnusedResourceBinding(
+      UnusedResourceBinding(H.GetHLOptions().bUnusedResourceBinding));
   // bool m_bDisableMathRefactoring;
   // bool m_bEnableDoublePrecision;
   // bool m_bEnableDoubleExtensions;

diff --git a/lib/HLSL/HLModule.cpp b/lib/HLSL/HLModule.cpp
@@ -231,17 +231,20 @@ void HLModule::RemoveFunction(llvm::Function *F) {
 namespace {
 template <typename TResource>
 bool RemoveResource(std::vector<std::unique_ptr<TResource>> &vec,
-                    GlobalVariable *pVariable, bool keepAllocated) {
+                    GlobalVariable *pVariable, bool keepAllocated,
+                    UnusedResourceBinding unusedResourceBinding) {
   for (auto p = vec.begin(), e = vec.end(); p != e; ++p) {
     if ((*p)->GetGlobalSymbol() != pVariable)
       continue;
 
-    if (keepAllocated && (*p)->IsAllocated()) {
+    if ((keepAllocated && (*p)->IsAllocated()) ||
+        unusedResourceBinding == UnusedResourceBinding::ReserveAll) {
       // Keep the resource, but it has no more symbol.
       (*p)->SetGlobalSymbol(UndefValue::get(pVariable->getType()));
     } else {
       // Erase the resource alltogether and update IDs of subsequent ones
       p = vec.erase(p);
+
       for (e = vec.end(); p != e; ++p) {
         unsigned ID = (*p)->GetID() - 1;
         (*p)->SetID(ID);
@@ -262,16 +265,19 @@ void HLModule::RemoveGlobal(llvm::GlobalVariable *GV) {
   // register range from being allocated to other resources.
   bool keepAllocated = GetHLOptions().bLegacyResourceReservation;
 
+  UnusedResourceBinding unusedResourceBinding =
+      UnusedResourceBinding(GetHLOptions().bUnusedResourceBinding);
+
   // This could be considerably faster - check variable type to see which
   // resource type this is rather than scanning all lists, and look for
   // usage and removal patterns.
-  if (RemoveResource(m_CBuffers, GV, keepAllocated))
+  if (RemoveResource(m_CBuffers, GV, keepAllocated, unusedResourceBinding))
     return;
-  if (RemoveResource(m_SRVs, GV, keepAllocated))
+  if (RemoveResource(m_SRVs, GV, keepAllocated, unusedResourceBinding))
     return;
-  if (RemoveResource(m_UAVs, GV, keepAllocated))
+  if (RemoveResource(m_UAVs, GV, keepAllocated, unusedResourceBinding))
     return;
-  if (RemoveResource(m_Samplers, GV, keepAllocated))
+  if (RemoveResource(m_Samplers, GV, keepAllocated, unusedResourceBinding))
     return;
   // TODO: do m_TGSMVariables and m_StreamOutputs need maintenance?
 }

diff --git a/tools/clang/include/clang/Frontend/CodeGenOptions.h b/tools/clang/include/clang/Frontend/CodeGenOptions.h
@@ -187,6 +187,9 @@ class CodeGenOptions : public CodeGenOptionsBase {
   bool HLSLOnlyWarnOnUnrollFail = false;
   /// Whether use legacy resource reservation.
   bool HLSLLegacyResourceReservation = false;
+  /// How to handle unused resource bindings.
+  hlsl::UnusedResourceBinding HLSLUnusedResourceBinding =
+      hlsl::UnusedResourceBinding::Strip;
   /// Set [branch] on every if.
   bool HLSLPreferControlFlow = false;
   /// Set [flatten] on every if.

diff --git a/tools/clang/lib/CodeGen/CGHLSLMS.cpp b/tools/clang/lib/CodeGen/CGHLSLMS.cpp
@@ -400,6 +400,8 @@ CGMSHLSLRuntime::CGMSHLSLRuntime(CodeGenModule &CGM)
   opts.PackingStrategy = CGM.getCodeGenOpts().HLSLSignaturePackingStrategy;
   opts.bLegacyResourceReservation =
       CGM.getCodeGenOpts().HLSLLegacyResourceReservation;
+  opts.bUnusedResourceBinding =
+      unsigned(CGM.getCodeGenOpts().HLSLUnusedResourceBinding);
   opts.bForceZeroStoreLifetimes =
       CGM.getCodeGenOpts().HLSLForceZeroStoreLifetimes;