From bbd1e1786401bb88c34802b987d4da72e2364503 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Wed, 1 Feb 2023 14:18:57 -0800
Subject: Support `out` parameters in backward differentiation. (#2619)

* Support `out` parameters in backward differentiation.

* Fixes.

* Fix cleanup.

---------

Co-authored-by: Yong He <yhe@nvidia.com>
---
 .../slang/slang-ir-autodiff-transcriber-base.cpp   | 65 ++++------------------
 1 file changed, 11 insertions(+), 54 deletions(-)

(limited to 'source/slang/slang-ir-autodiff-transcriber-base.cpp')

diff --git a/source/slang/slang-ir-autodiff-transcriber-base.cpp b/source/slang/slang-ir-autodiff-transcriber-base.cpp
index 520c6d276..8f21e8c62 100644
--- a/source/slang/slang-ir-autodiff-transcriber-base.cpp
+++ b/source/slang/slang-ir-autodiff-transcriber-base.cpp
@@ -17,16 +17,6 @@ DiagnosticSink* AutoDiffTranscriberBase::getSink()
     return sink;
 }
 
-String AutoDiffTranscriberBase::makeDiffPairName(IRInst* origVar)
-{
-    if (auto namehintDecoration = origVar->findDecoration<IRNameHintDecoration>())
-    {
-        return ("dp" + String(namehintDecoration->getName()));
-    }
-
-    return String("");
-}
-
 void AutoDiffTranscriberBase::mapDifferentialInst(IRInst* origInst, IRInst* diffInst)
 {
     if (hasDifferentialInst(origInst))
@@ -523,46 +513,7 @@ InstPair AutoDiffTranscriberBase::transcribeParam(IRBuilder* builder, IRParam* o
     bool isFuncParam = (func && origParam->getParent() == func->getFirstBlock());
     if (isFuncParam)
     {
-        if (auto diffPairType = tryGetDiffPairType(builder, (IRType*)primalDataType))
-        {
-            IRInst* diffPairParam = builder->emitParam(diffPairType);
-
-            auto diffPairVarName = makeDiffPairName(origParam);
-            if (diffPairVarName.getLength() > 0)
-                builder->addNameHintDecoration(diffPairParam, diffPairVarName.getUnownedSlice());
-
-            SLANG_ASSERT(diffPairParam);
-
-            if (auto pairType = as<IRDifferentialPairType>(diffPairType))
-            {
-                return InstPair(
-                    builder->emitDifferentialPairGetPrimal(diffPairParam),
-                    builder->emitDifferentialPairGetDifferential(
-                        (IRType*)pairBuilder->getDiffTypeFromPairType(builder, pairType),
-                        diffPairParam));
-            }
-            else if (auto pairPtrType = as<IRPtrTypeBase>(diffPairType))
-            {
-                auto ptrInnerPairType = as<IRDifferentialPairType>(pairPtrType->getValueType());
-
-                return InstPair(
-                    builder->emitDifferentialPairAddressPrimal(diffPairParam),
-                    builder->emitDifferentialPairAddressDifferential(
-                        builder->getPtrType(
-                            kIROp_PtrType,
-                            (IRType*)pairBuilder->getDiffTypeFromPairType(builder, ptrInnerPairType)),
-                        diffPairParam));
-            }
-        }
-
-        auto primalInst = cloneInst(&cloneEnv, builder, origParam);
-        if (auto primalParam = as<IRParam>(primalInst))
-        {
-            SLANG_RELEASE_ASSERT(builder->getInsertLoc().getBlock());
-            primalParam->removeFromParent();
-            builder->getInsertLoc().getBlock()->addParam(primalParam);
-        }
-        return InstPair(primalInst, nullptr);
+        return transcribeFuncParam(builder, origParam, primalDataType);
     }
     else
     {
@@ -617,10 +568,14 @@ IRInst* AutoDiffTranscriberBase::getDifferentialZeroOfType(IRBuilder* builder, I
         switch (diffType->getOp())
         {
         case kIROp_DifferentialPairType:
-            return builder->emitMakeDifferentialPair(
-                diffType,
-                getDifferentialZeroOfType(builder, as<IRDifferentialPairType>(diffType)->getValueType()),
-                getDifferentialZeroOfType(builder, as<IRDifferentialPairType>(diffType)->getValueType()));
+            {
+                auto makeDiffPair = builder->emitMakeDifferentialPair(
+                    diffType,
+                    getDifferentialZeroOfType(builder, as<IRDifferentialPairType>(diffType)->getValueType()),
+                    getDifferentialZeroOfType(builder, as<IRDifferentialPairType>(diffType)->getValueType()));
+                builder->markInstAsDifferential(makeDiffPair, as<IRDifferentialPairType>(diffType)->getValueType());
+                return makeDiffPair;
+            }
         }
 
         if (auto arrayType = as<IRArrayType>(primalType))
@@ -647,6 +602,7 @@ IRInst* AutoDiffTranscriberBase::getDifferentialZeroOfType(IRBuilder* builder, I
             {
                 auto wt = lookupInterface->getWitnessTable();
                 zeroMethod = builder->emitLookupInterfaceMethodInst(builder->getFuncType(List<IRType*>(), diffType), wt, autoDiffSharedContext->zeroMethodStructKey);
+                builder->markInstAsDifferential(zeroMethod);
             }
         }
         SLANG_RELEASE_ASSERT(zeroMethod);
@@ -759,6 +715,7 @@ InstPair AutoDiffTranscriberBase::transcribeReturn(IRBuilder* builder, IRReturn*
         IRInst* primalReturnVal = findOrTranscribePrimalInst(builder, origReturnVal);
 
         IRInst* primalReturn = builder->emitReturn(primalReturnVal);
+        builder->markInstAsMixedDifferential(primalReturn, nullptr);
         return InstPair(primalReturn, nullptr);
 
     }
-- 
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