[SPIR-V] Add descriptor heap RaytracingAccelerationStructure support

Extends the SPV_EXT_descriptor_heap native heap lowering to cover RaytracingAccelerationStructure resources loaded from ResourceDescriptorHeap.

Acceleration structure descriptors are accessed via OpUntypedAccessChainKHR into a runtime array of OpTypeAccelerationStructureKHR, consistent with the image and sampler paths added in the previous commit.

Author: jzakharovnv

tools/clang/include/clang/SPIRV/AstTypeProbe.h

@@ -250,6 +250,10 @@ bool isBuffer(QualType type);
 /// \brief Returns true if the given type is the HLSL RWBuffer type.
 bool isRWBuffer(QualType type);
 
+/// \brief Returns true if the given type is the HLSL
+/// RaytracingAccelerationStructure type.
+bool isRaytracingAccelerationStructure(QualType type);
+
 /// \brief Returns true if the given type is an HLSL Texture type.
 bool isTexture(QualType);
 

tools/clang/lib/SPIRV/AstTypeProbe.cpp

@@ -917,6 +917,13 @@ bool isBuffer(QualType type) {
   return false;
 }
 
+bool isRaytracingAccelerationStructure(QualType type) {
+  if (const auto *rt = type->getAs<RecordType>()) {
+    return rt->getDecl()->getName() == "RaytracingAccelerationStructure";
+  }
+  return false;
+}
+
 bool isRWTexture(QualType type) {
   if (const auto *rt = type->getAs<RecordType>()) {
     const auto name = rt->getDecl()->getName();

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -2039,6 +2039,16 @@ bool SpirvEmitter::tryToCreateDescriptorHeapAlias(const VarDecl *decl,
     return true;
   }
 
+  if (isRaytracingAccelerationStructure(decl->getType())) {
+    if (auto *initVal = loadIfGLValue(init))
+      declIdMapper.registerFnVarAlias(decl, initVal);
+    else
+      emitError("cannot create descriptor heap acceleration structure alias "
+                "from initializer",
+                init->getExprLoc());
+    return true;
+  }
+
   return false;
 }
 

tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.acceleration-structure.hlsl

@@ -0,0 +1,42 @@
+// RUN: %dxc -T lib_6_6 -fspv-use-descriptor-heap -fspv-target-env=vulkan1.3 -fvk-resource-heap-stride 64 -fvk-sampler-heap-stride 32 -fspv-extension=SPV_KHR_ray_tracing -fspv-extension=SPV_EXT_descriptor_heap -fspv-extension=SPV_KHR_untyped_pointers -spirv %s | FileCheck %s
+
+// Verifies: ResourceDescriptorHeap of a RaytracingAccelerationStructure 
+//  lowers to an acceleration-structure runtime array, loads the accel 
+//  handle from the heap, and emits OpTraceRayKHR under the ray-tracing 
+//  capability/extension.
+
+// CHECK:                                                 OpCapability RayTracingKHR
+// CHECK:                                                 OpExtension "SPV_KHR_ray_tracing"
+
+// CHECK-DAG: %[[UntypedUniformConstant:[a-zA-Z0-9_]+]] = OpTypeUntypedPointerKHR UniformConstant
+// CHECK-DAG:                  %[[Accel:[a-zA-Z0-9_]+]] = OpTypeAccelerationStructureKHR
+// CHECK-DAG:                %[[ASArray:[a-zA-Z0-9_]+]] = OpTypeRuntimeArray %[[Accel]]
+// CHECK:               %[[ResourceHeap:[a-zA-Z0-9_]+]] = OpUntypedVariableKHR %[[UntypedUniformConstant]] UniformConstant
+
+struct Payload {
+  float4 color;
+};
+
+struct Attribute {
+  float2 bary;
+};
+
+[shader("closesthit")]
+void main(inout Payload payload, in Attribute attr) {
+  RaytracingAccelerationStructure scene = ResourceDescriptorHeap[3];
+
+  RayDesc ray;
+  ray.Origin = float3(0.0f, 0.0f, 0.0f);
+  ray.Direction = float3(0.0f, 0.0f, -1.0f);
+  ray.TMin = 0.0f;
+  ray.TMax = 1000.0f;
+
+  Payload childPayload = { float4(attr.bary, 0.0f, 1.0f) };
+
+  // CHECK:                     %[[Desc:[a-zA-Z0-9_]+]] = OpUntypedAccessChainKHR %[[UntypedUniformConstant]] %[[ASArray]] %[[ResourceHeap]] %uint_3
+  // CHECK:                    %[[Scene:[a-zA-Z0-9_]+]] = OpLoad %[[Accel]] %[[Desc]]
+  // CHECK:                                               OpTraceRayKHR %[[Scene]]
+  TraceRay(scene, 0x0, 0xff, 0, 1, 0, ray, childPayload);
+
+  payload.color = childPayload.color;
+}