Bug fix for optix SBT access (shader-slang#1922)

* optix SBT record data can now be accessed using uniform parameters on ray tracing entry points

* Update slang-emit.cpp

* fixing a bug where SBT instruction was missing a location at which to insert. Switching back to emitFieldExtract and accounting for changes in instruction emission location

Author: natevm

source/slang/slang-emit-cuda.cpp

@@ -813,9 +813,9 @@ bool CUDASourceEmitter::tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inOu
         }
         case kIROp_GetOptiXSbtDataPtr:
         {
-            m_writer->emit("(*((");
+            m_writer->emit("((");
             emitType(inst->getDataType());
-            m_writer->emit(")optixGetSbtDataPointer()))");
+            m_writer->emit(")optixGetSbtDataPointer())");
             return true;
         }
         default: break;

source/slang/slang-ir-optix-entry-point-uniforms.cpp

@@ -234,15 +234,16 @@ struct CollectOptixEntryPointUniformParams : PerEntryPointPass {
                 //
                 IRInst* fieldVal = nullptr;
 
-                // Note: for an optix SBT pointer, we can't dereference
-                // optixGetSbtDataPointer() like builder->emitFieldAddress requires.
-                // (thus, this code differs from slang-ir-entry-point-uniforms.cpp)
-                // Instead, we always use emitFieldExtract, and then the SBT instruction
-                // emits a C-style cast to the appropriate struct type.
-                fieldVal = builder->emitFieldExtract(
-                    paramType,
+                // A constant buffer behaves like a pointer
+                // at the IR level, so we first do a pointer
+                // offset operation to compute what amounts
+                // to `&cb->field`, and then load from that address.
+                //
+                auto fieldAddress = builder->emitFieldAddress(
+                    builder->getPtrType(paramType),
                     collectedParam,
                     paramFieldKey);
+                fieldVal = builder->emitLoad(fieldAddress);
 
                 // We replace the value used at this use site, which
                 // will have a side effect of making `use` no longer
@@ -270,6 +271,7 @@ struct CollectOptixEntryPointUniformParams : PerEntryPointPass {
 
         // Now, replace the collected parameter with OptiX SBT accesses.
         auto paramType = collectedParam->getFullType();
+        builder->setInsertBefore(entryPointFunc->getFirstBlock()->getFirstOrdinaryInst());
         IRInst* getAttr = builder->emitIntrinsicInst(paramType, kIROp_GetOptiXSbtDataPtr, 0, nullptr);
         collectedParam->replaceUsesWith(getAttr);
         collectedParam->removeAndDeallocate();