Added support for differentiating out and inout parameters. (#2323)

* Added out/inout tests

* Added support for out and inout parameters. Still untested

* Fixed and tested support for out and inout types

* Removed some comments

1 files changed, 89 insertions, 17 deletions

diff --git a/source/slang/slang-ir-diff-jvp.cpp b/source/slang/slang-ir-diff-jvp.cpp
index 5b77d483d..f5afccd0c 100644
--- a/source/slang/slang-ir-diff-jvp.cpp
+++ b/source/slang/slang-ir-diff-jvp.cpp
@@ -56,7 +56,9 @@ struct JVPTranscriber
         // Add all primal parameters to the list.
         for (UIndex i = 0; i < funcType->getParamCount(); i++)
         {   
-            parameterTypesD.add(funcType->getParamType(i));
+            // TODO(sai): Move this check to a separate function.
+            if (!as<IROutType>(funcType->getParamType(i)))
+                parameterTypesD.add(funcType->getParamType(i));
         }
 
         // Add differential versions for the types we support.
@@ -85,7 +87,12 @@ struct JVPTranscriber
             case kIROp_DoubleType:
                 return builder->getType(typeP->getOp());
             case kIROp_VectorType:
+                // TODO(sai): Call differentiateType() on typeP.
                 return as<IRVectorType>(typeP);
+            case kIROp_OutType:
+                return builder->getOutType(differentiateType(builder, as<IROutType>(typeP)->getValueType()));
+            case kIROp_InOutType:
+                return builder->getInOutType(differentiateType(builder, as<IRInOutType>(typeP)->getValueType()));
             default:
                 return nullptr;
         }
@@ -102,21 +109,45 @@ struct JVPTranscriber
         return nullptr;
     }
 
+    IRInst* emitInputParam(IRBuilder* builder, IRParam* paramP)
+    {
+        // Convert primal 'inout' types into pure input types, because a
+        // JVP transformed function must never have primal side-effects.
+        // 
+        if (auto inoutTypeP = as<IRInOutType>(paramP->getDataType()))
+        {   
+            auto newParamP = builder->emitParam(inoutTypeP->getValueType());
+            cloneEnv.mapOldValToNew.Add(paramP, newParamP);
+
+            return newParamP;
+        }
+        else if (as<IROutType>(paramP->getDataType()))
+        {
+            getSink()->diagnose(paramP->sourceLoc,
+                    Diagnostics::unexpected,
+                    "encountered unexpected output parameter");
+            return nullptr;
+        }
+        else
+            return as<IRParam>(cloneInst(&cloneEnv, builder, paramP));
+    }
+
     List<IRParam*> transcribeParams(IRBuilder* builder, IRInstList<IRParam> paramListP)
     {
         // Clone (and emit) all the primal parameters.
         List<IRParam*> newParamListP;
         for (auto paramP : paramListP)
         {
-            newParamListP.add(as<IRParam>(cloneInst(&cloneEnv, builder, paramP)));
+            if(requiresPrimalClone(builder, paramP))
+                newParamListP.add(as<IRParam>(emitInputParam(builder, paramP)));
         }
 
         // Now emit differentials.
         List<IRParam*> newParamListD;
-        for (auto paramP : newParamListP)
+        for (auto paramP : paramListP)
         {
             IRParam* paramD = as<IRParam>(differentiateParam(builder, paramP));
-            mapDifferentialInst(paramP, paramD);
+            mapDifferentialInst(findCloneForOperand(&cloneEnv, paramP), paramD);
             newParamListD.add(paramD);
         }
 
@@ -187,15 +218,16 @@ struct JVPTranscriber
 
     IRInst* differentiateLoad(IRBuilder* builder, IRLoad* loadP)
     {
-        if (auto varP = as<IRVar>(loadP->getPtr()))
+        auto ptrP = loadP->getPtr();
+        if (as<IRVar>(ptrP) || as<IRParam>(ptrP))
         {   
             // If the loaded parameter has a differential version, 
             // emit a load instruction for the differential parameter.
             // Otherwise, emit nothing since there's nothing to load.
             // 
-            if (auto varD = as<IRVar>(getDifferentialInst(varP)))
+            if (auto ptrD = getDifferentialInst(ptrP, nullptr))
             {
-                IRLoad* loadD = as<IRLoad>(builder->emitLoad(varD));
+                IRLoad* loadD = as<IRLoad>(builder->emitLoad(ptrD));
                 SLANG_ASSERT(loadD);
                 return loadD;
             }
@@ -212,14 +244,14 @@ struct JVPTranscriber
     {
         IRInst* storeLocation = storeP->getPtr();
         IRInst* storeVal = storeP->getVal();
-        if (auto destParam = as<IRVar>(storeLocation))
+        if (as<IRVar>(storeLocation) || as<IRParam>(storeLocation))
         {   
             // If the stored value has a differential version, 
             // emit a store instruction for the differential parameter.
             // Otherwise, emit nothing since there's nothing to load.
             // 
             IRInst* storeValD = getDifferentialInst(storeVal);
-            IRVar*  storeLocationD = as<IRVar>(getDifferentialInst(destParam));
+            IRInst* storeLocationD = getDifferentialInst(storeLocation);
             if (storeValD && storeLocationD)
             {
                 IRStore* storeD = as<IRStore>(
@@ -239,13 +271,18 @@ struct JVPTranscriber
     IRInst* differentiateReturn(IRBuilder* builder, IRReturn* returnP)
     {
         IRInst* returnVal = findCloneForOperand(&cloneEnv, returnP->getVal());
-        if (auto returnValD = getDifferentialInst(returnVal))
+        if (auto returnValD = getDifferentialInst(returnVal, nullptr))
         {   
             IRReturn* returnD = as<IRReturn>(builder->emitReturn(returnValD));
             SLANG_ASSERT(returnD);
             return returnD;
         }
-        return nullptr;
+        else
+        {
+            // If the differential return value is not available, emit a 
+            // void return.
+            return builder->emitReturn();
+        }
     }
 
     // Since int/float literals are sometimes nested inside an IRConstructor
@@ -352,16 +389,38 @@ struct JVPTranscriber
     }
 
     // Logic for whether a primal instruction needs to be replicated
-    // in the differential function. For puerly functional blocks with
-    // no side-effects, it's safe to replicate everything except the
-    // return instruction.
-    //
+    // in the differential function. We detect and avoid replicating 
+    // side-effect instructions.
+    // 
     bool requiresPrimalClone(IRBuilder*, IRInst* instP)
     {
         if (as<IRReturn>(instP))
             return false;
-        else
-            return true;
+        else if (auto paramP = as<IRParam>(instP))
+        {
+            // Out-type parameters are discarded from the parameter list,
+            // since pure JVP functions to not write to primal outputs.
+            // 
+            if (as<IROutType>(paramP->getDataType()))
+                return false;
+        }
+        else if (auto storeP = as<IRStore>(instP))
+        {
+            IRInst* storeLocation = storeP->getPtr();
+
+            // Writing to a parameter is a side-effect that should be avoided.
+            if(as<IRParam>(storeLocation))
+                return false;
+
+            // If attempting to store to a location without a clone, 
+            // then this instruction likely has side-effects external to the
+            // current function.
+            // 
+            if(!lookUp(&cloneEnv, storeLocation))
+                return false;
+        }
+        
+        return true;
     }
 
     IRInst* transcribe(IRBuilder* builder, IRInst* oldInstP)
@@ -374,6 +433,19 @@ struct JVPTranscriber
         //
         if (requiresPrimalClone(builder, oldInstP))
             instP = cloneInst(&cloneEnv, builder, oldInstP);
+        else
+        {
+            // We replace the operands of the old instruction with their clones,
+            // if available.
+            // 
+            for(UInt ii = 0; ii < oldInstP->getOperandCount(); ++ii)
+            {
+                auto oldOperand = oldInstP->getOperand(ii);
+                auto newOperand = findCloneForOperand(&cloneEnv, oldOperand);
+
+                instP->getOperands()[ii].init(instP, newOperand);
+            }
+        }
         SLANG_ASSERT(instP);
 
         IRInst* instD = differentiateInst(builder, instP);