Complete removal of DifferentialBottom type. (#2537)

Co-authored-by: Yong He <yhe@nvidia.com>

10 files changed, 42 insertions, 171 deletions

diff --git a/source/slang/core.meta.slang b/source/slang/core.meta.slang
index 8cfa85983..73a004720 100644
--- a/source/slang/core.meta.slang
+++ b/source/slang/core.meta.slang
@@ -132,28 +132,6 @@ interface IDifferentiable
     static Differential dmul(This, Differential);
 };
 
-__magic_type(DifferentialBottomType)
-__intrinsic_type($(kIROp_DifferentialBottomType))
-struct __DifferentialBottom : IDifferentiable
-{
-    typedef __DifferentialBottom Differential;
-
-    __intrinsic_op($(kIROp_DifferentialBottomValue))
-    static __DifferentialBottom dzero();
-
-    [__unsafeForceInlineEarly]
-    static __DifferentialBottom dadd(Differential a, Differential b)
-    {
-        return dzero();
-    }
-
-    [__unsafeForceInlineEarly]
-    static __DifferentialBottom dmul(This a, Differential b)
-    {
-        return dzero();
-    }
-}
-
 /// A type that can represent non-integers
 [sealed]
 [builtin]
diff --git a/source/slang/slang-ast-builder.cpp b/source/slang/slang-ast-builder.cpp
index 819fe7d25..d8fec88ce 100644
--- a/source/slang/slang-ast-builder.cpp
+++ b/source/slang/slang-ast-builder.cpp
@@ -141,16 +141,6 @@ Type* SharedASTBuilder::getNoneType()
     return m_noneType;
 }
 
-Type* SharedASTBuilder::getDifferentialBottomType()
-{
-    if (!m_diffBottomType)
-    {
-        auto diffBottomTypeDecl = findMagicDecl("DifferentialBottomType");
-        m_diffBottomType = DeclRefType::create(m_astBuilder, makeDeclRef<Decl>(diffBottomTypeDecl));
-    }
-    return m_diffBottomType;
-}
-
 SharedASTBuilder::~SharedASTBuilder()
 {
     // Release built in types..
diff --git a/source/slang/slang-ast-builder.h b/source/slang/slang-ast-builder.h
index 6c0e1af36..f011feae8 100644
--- a/source/slang/slang-ast-builder.h
+++ b/source/slang/slang-ast-builder.h
@@ -36,8 +36,6 @@ public:
     Type* getNullPtrType();
         /// Get the NullPtr type
     Type* getNoneType();
-        /// Get the DifferentialBottom type.
-    Type* getDifferentialBottomType();
 
     const ReflectClassInfo* findClassInfo(Name* name);
     SyntaxClass<NodeBase> findSyntaxClass(Name* name);
@@ -306,7 +304,6 @@ public:
     Type* getOverloadedType() { return m_sharedASTBuilder->m_overloadedType; }
     Type* getErrorType() { return m_sharedASTBuilder->m_errorType; }
     Type* getBottomType() { return m_sharedASTBuilder->m_bottomType; }
-    Type* getDifferentialBottomType() { return m_sharedASTBuilder->getDifferentialBottomType(); }
     Type* getStringType() { return m_sharedASTBuilder->getStringType(); }
     Type* getNullPtrType() { return m_sharedASTBuilder->getNullPtrType(); }
     Type* getNoneType() { return m_sharedASTBuilder->getNoneType(); }
diff --git a/source/slang/slang-ast-type.cpp b/source/slang/slang-ast-type.cpp
index 3fcc762ec..3801b99b0 100644
--- a/source/slang/slang-ast-type.cpp
+++ b/source/slang/slang-ast-type.cpp
@@ -169,27 +169,6 @@ Val* BottomType::_substituteImplOverride(
 
 HashCode BottomType::_getHashCodeOverride() { return HashCode(size_t(this)); }
 
-// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! DifferentialBottomType !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-
-void DifferentialBottomType::_toTextOverride(StringBuilder& out) { out << toSlice("diff_bottom"); }
-
-bool DifferentialBottomType::_equalsImplOverride(Type* type)
-{
-    if (auto bottomType = as<DifferentialBottomType>(type))
-        return true;
-    return false;
-}
-
-Type* DifferentialBottomType::_createCanonicalTypeOverride() { return this; }
-
-Val* DifferentialBottomType::_substituteImplOverride(
-    ASTBuilder* /* astBuilder */, SubstitutionSet /*subst*/, int* /*ioDiff*/)
-{
-    return this;
-}
-
-HashCode DifferentialBottomType::_getHashCodeOverride() { return HashCode(size_t(this)); }
-
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! DeclRefType !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 void DeclRefType::_toTextOverride(StringBuilder& out)
diff --git a/source/slang/slang-ast-type.h b/source/slang/slang-ast-type.h
index 8953f0b10..f19b71b56 100644
--- a/source/slang/slang-ast-type.h
+++ b/source/slang/slang-ast-type.h
@@ -86,20 +86,6 @@ protected:
     {}
 };
 
-// The bottom/empty type as a result of Differentiating a Differential.
-class DifferentialBottomType : public DeclRefType
-{
-    SLANG_AST_CLASS(DifferentialBottomType)
-
-    // Overrides should be public so base classes can access
-    void _toTextOverride(StringBuilder& out);
-    Type* _createCanonicalTypeOverride();
-    bool _equalsImplOverride(Type* type);
-    HashCode _getHashCodeOverride();
-    Val* _substituteImplOverride(ASTBuilder* astBuilder, SubstitutionSet subst, int* ioDiff);
-};
-
-
 // Base class for types that can be used in arithmetic expressions
 class ArithmeticExpressionType : public DeclRefType 
 {
diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 4d2839b8d..5e6c6eedf 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -259,8 +259,6 @@ namespace Slang
 
         void visitParamDecl(ParamDecl* paramDecl);
 
-        void _maybeRegisterDifferentialBottomTypeConformance(SemanticsContext& context);
-
         void checkDerivativeOfAttribute(FunctionDeclBase* funcDecl);
 
         void checkDerivativeAttribute(FunctionDeclBase* funcDecl, ForwardDerivativeAttribute* attr);
@@ -3317,73 +3315,52 @@ namespace Slang
         auto seqStmt = synth.pushSeqStmtScope();
         blockStmt->body = seqStmt;
 
-        if (synFunc->returnType.type->equals(m_astBuilder->getDifferentialBottomType()))
-        {
-            // Trivial case, the `Differential` type is `DifferentialBottom`.
-            // We will just return `DifferentialBottom.dzero()`.
-            auto resultExpr = m_astBuilder->create<InvokeExpr>();
-            auto dzeroMember = m_astBuilder->create<StaticMemberExpr>();
-            auto base = m_astBuilder->create<SharedTypeExpr>();
-            auto typetype = m_astBuilder->create<TypeType>();
-            typetype->type = m_astBuilder->getDifferentialBottomType();
-            base->type.type = typetype;
-            dzeroMember->baseExpression = base;
-            dzeroMember->name = getName("dzero");
-            resultExpr->functionExpr = dzeroMember;
-            auto synReturn = m_astBuilder->create<ReturnStmt>();
-            synReturn->expression = resultExpr;
-            seqStmt->stmts.add(synReturn);
-        }
-        else
-        {
-            // The general case. 
-            // Create a variable for return value.
-            synth.pushVarScope();
-            auto varStmt = synth.emitVarDeclStmt(synFunc->returnType.type, getName("result"));
-            auto resultVarExpr = synth.emitVarExpr(varStmt, synFunc->returnType.type);
+        // Create a variable for return value.
+        synth.pushVarScope();
+        auto varStmt = synth.emitVarDeclStmt(synFunc->returnType.type, getName("result"));
+        auto resultVarExpr = synth.emitVarExpr(varStmt, synFunc->returnType.type);
 
-            for (auto member : context->parentDecl->members)
-            {
-                auto derivativeAttr = member->findModifier<DerivativeMemberAttribute>();
-                if (!derivativeAttr)
-                    continue;
-                auto varMember = as<VarDeclBase>(member);
-                if (!varMember)
-                    continue;
-                ensureDecl(varMember, DeclCheckState::ReadyForReference);
-                auto memberType = varMember->getType();
-                auto diffMemberType = tryGetDifferentialType(m_astBuilder, memberType);
-                if (!diffMemberType)
-                    continue;
-
-                // Construct reference exprs to the member's corresponding fields in each parameter.
-                List<Expr*> paramFields;
-                int paramIndex = 0;
-                for (auto arg : synArgs)
-                {
-                    auto memberExpr = m_astBuilder->create<MemberExpr>();
-                    memberExpr->baseExpression = arg;
-                    // TODO: we should probably fetch the name from `[DerivativeMember]` if `arg` is
-                    // Differential type.
-                    memberExpr->name = varMember->getName();
-                    paramFields.add(memberExpr);
-                    paramIndex++;
-                }
+        for (auto member : context->parentDecl->members)
+        {
+            auto derivativeAttr = member->findModifier<DerivativeMemberAttribute>();
+            if (!derivativeAttr)
+                continue;
+            auto varMember = as<VarDeclBase>(member);
+            if (!varMember)
+                continue;
+            ensureDecl(varMember, DeclCheckState::ReadyForReference);
+            auto memberType = varMember->getType();
+            auto diffMemberType = tryGetDifferentialType(m_astBuilder, memberType);
+            if (!diffMemberType)
+                continue;
 
-                // Invoke the method for the field and assign the value to resultVar.
-                // TODO: we should probably fetch the name from `[DerivativeMember]` if `resultVarExpr`
-                // is Differential type.
-                auto leftVal = synth.emitMemberExpr(resultVarExpr, varMember->getName());
-                if (!_synthesizeMemberAssignMemberHelper(synth, requirementDeclRef.getName(), memberType, leftVal, _Move(paramFields)))
-                    return false;
-            }
+            // Construct reference exprs to the member's corresponding fields in each parameter.
+            List<Expr*> paramFields;
+            int paramIndex = 0;
+            for (auto arg : synArgs)
+            {
+                auto memberExpr = m_astBuilder->create<MemberExpr>();
+                memberExpr->baseExpression = arg;
+                // TODO: we should probably fetch the name from `[DerivativeMember]` if `arg` is
+                // Differential type.
+                memberExpr->name = varMember->getName();
+                paramFields.add(memberExpr);
+                paramIndex++;
+            }
+
+            // Invoke the method for the field and assign the value to resultVar.
+            // TODO: we should probably fetch the name from `[DerivativeMember]` if `resultVarExpr`
+            // is Differential type.
+            auto leftVal = synth.emitMemberExpr(resultVarExpr, varMember->getName());
+            if (!_synthesizeMemberAssignMemberHelper(synth, requirementDeclRef.getName(), memberType, leftVal, _Move(paramFields)))
+                return false;
+        }
 
-            // TODO: synthesize assignments for inherited members here.
+        // TODO: synthesize assignments for inherited members here.
 
-            auto synReturn = m_astBuilder->create<ReturnStmt>();
-            synReturn->expression = resultVarExpr;
-            seqStmt->stmts.add(synReturn);
-        }
+        auto synReturn = m_astBuilder->create<ReturnStmt>();
+        synReturn->expression = resultVarExpr;
+        seqStmt->stmts.add(synReturn);
         
         context->parentDecl->members.add(synFunc);
         context->parentDecl->invalidateMemberDictionary();
@@ -4633,21 +4610,6 @@ namespace Slang
             getSink()->diagnose(decl, Slang::Diagnostics::assocTypeInInterfaceOnly);
     }
 
-    void SemanticsDeclBodyVisitor::_maybeRegisterDifferentialBottomTypeConformance(SemanticsContext& context)
-    {
-        auto parentDifferentiableAttr = context.getParentDifferentiableAttribute();
-        if (parentDifferentiableAttr)
-        {
-            auto diffBottomType = m_astBuilder->getDifferentialBottomType();
-            auto idifferentiable = DeclRef<InterfaceDecl>(m_astBuilder->getDifferentiableInterface(), nullptr);
-            auto witness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(diffBottomType, idifferentiable));
-            SLANG_ASSERT(witness);
-            parentDifferentiableAttr->m_mapTypeToIDifferentiableWitness.Add(
-                as<DeclRefType>(diffBottomType)->declRef,
-                witness);
-        }
-    }
-
     void SemanticsDeclBodyVisitor::checkDerivativeOfAttribute(FunctionDeclBase* funcDecl)
     {
         auto attr = funcDecl->findModifier<ForwardDerivativeOfAttribute>();
diff --git a/source/slang/slang-ir-inst-defs.h b/source/slang/slang-ir-inst-defs.h
index 9233972ad..3ca9f1d41 100644
--- a/source/slang/slang-ir-inst-defs.h
+++ b/source/slang/slang-ir-inst-defs.h
@@ -60,7 +60,6 @@ INST(Nop, nop, 0, 0)
     INST(OptionalType, Optional, 1, 0)
 
     INST(DifferentialPairType, DiffPair, 1, 0)
-    INST(DifferentialBottomType, DiffBottomType, 0, 0)
 
     /* BindExistentialsTypeBase */
 
diff --git a/source/slang/slang-ir-insts.h b/source/slang/slang-ir-insts.h
index 250088f96..7cf8b3032 100644
--- a/source/slang/slang-ir-insts.h
+++ b/source/slang/slang-ir-insts.h
@@ -2439,7 +2439,6 @@ public:
     IRAnyValueType* getAnyValueType(IRIntegerValue size);
     IRAnyValueType* getAnyValueType(IRInst* size);
     IRDynamicType* getDynamicType();
-    IRDifferentialBottomType* getDifferentialBottomType();
 
     IRTupleType* getTupleType(UInt count, IRType* const* types);
     IRTupleType* getTupleType(List<IRType*> const& types)
diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index c12872320..ecfcab7f5 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -2214,17 +2214,6 @@ namespace Slang
         return _findOrEmitConstant(keyInst);
     }
 
-    IRInst* IRBuilder::getDifferentialBottom()
-    {
-        IRType* type = getDifferentialBottomType();
-        IRConstant keyInst;
-        memset(&keyInst, 0, sizeof(keyInst));
-        keyInst.m_op = kIROp_DifferentialBottomValue;
-        keyInst.typeUse.usedValue = type;
-        keyInst.value.intVal = 0;
-        return (IRInst*)_findOrEmitConstant(keyInst);
-    }
-
     IRStringLit* IRBuilder::getStringValue(const UnownedStringSlice& inSlice)
     {
         IRConstant keyInst;
@@ -2607,12 +2596,6 @@ namespace Slang
 
     IRDynamicType* IRBuilder::getDynamicType() { return (IRDynamicType*)getType(kIROp_DynamicType); }
 
-    IRDifferentialBottomType* IRBuilder::getDifferentialBottomType()
-    {
-        return (IRDifferentialBottomType*)getType(kIROp_DifferentialBottomType);
-    }
-
-
     IRAssociatedType* IRBuilder::getAssociatedType(ArrayView<IRInterfaceType*> constraintTypes)
     {
         return (IRAssociatedType*)getType(kIROp_AssociatedType,
diff --git a/source/slang/slang-ir.h b/source/slang/slang-ir.h
index ab3f010b0..0909615af 100644
--- a/source/slang/slang-ir.h
+++ b/source/slang/slang-ir.h
@@ -864,8 +864,6 @@ SIMPLE_IR_TYPE(NativeStringType, StringTypeBase)
 
 SIMPLE_IR_TYPE(DynamicType, Type)
 
-SIMPLE_IR_TYPE(DifferentialBottomType, Type)
-
 // True if types are equal
 // Note compares nominal types by name alone 
 bool isTypeEqual(IRType* a, IRType* b);