Remove GlobalGenericParamSubstitution (#1684)

The `GlobalGenericParamSubsitution` class used to be used to represent the mapping of global-scope generic parameters to their concrete arguments, so that we could make use of those concrete arguments for things like layout. That representation caused a lot of pain for other parts of the compiler, though, because everything that dealt with `Substitution`s needed to account for the possibility of global-generic-param subsitutions even if they logically could not occur in most parts of the compiler.

We have since moved to a model where the values for global-scope generic parameters are stored in a single explicit global structure that is used by both layout computation and IR lowering. There is no actual code that construct `GlobalGenericParamSubstitution`s from scratch any more, so all of the support code for them was actually unused.

This change removes all the unused code, and shows that the tests still pass without it (even the tests that use global-scope generic parameters).

8 files changed, 1 insertions, 280 deletions

diff --git a/source/slang/slang-ast-base.h b/source/slang/slang-ast-base.h
index 2bfa7940b..b7810b49a 100644
--- a/source/slang/slang-ast-base.h
+++ b/source/slang/slang-ast-base.h
@@ -229,34 +229,6 @@ class ThisTypeSubstitution : public Substitutions
     HashCode _getHashCodeOverride() const;
 };
 
-struct GlobalGenericParamSubstitution_ConstraintArg
-{
-    SLANG_VALUE_CLASS(GlobalGenericParamSubstitution_ConstraintArg)
-    Decl*    decl = nullptr;
-    Val*     val = nullptr;
-};
-
-class GlobalGenericParamSubstitution : public Substitutions
-{
-    SLANG_AST_CLASS(GlobalGenericParamSubstitution)
-
-    typedef GlobalGenericParamSubstitution_ConstraintArg ConstraintArg;
-
-    // the type_param decl to be substituted
-    GlobalGenericParamDecl* paramDecl = nullptr;
-
-    // the actual type to substitute in
-    Type* actualType = nullptr;
-
-    // the values that satisfy any constraints on the type parameter
-    List<GlobalGenericParamSubstitution_ConstraintArg> constraintArgs;
-
-    // Overrides should be public so base classes can access
-    Substitutions* _applySubstitutionsShallowOverride(ASTBuilder* astBuilder, SubstitutionSet substSet, Substitutions* substOuter, int* ioDiff);
-    bool _equalsOverride(Substitutions* subst);
-    HashCode _getHashCodeOverride() const;
-};
-
 class SyntaxNode : public SyntaxNodeBase
 {
     SLANG_ABSTRACT_AST_CLASS(SyntaxNode);
diff --git a/source/slang/slang-ast-dump.cpp b/source/slang/slang-ast-dump.cpp
index 38dfa9c2f..9da1a0163 100644
--- a/source/slang/slang-ast-dump.cpp
+++ b/source/slang/slang-ast-dump.cpp
@@ -500,19 +500,6 @@ struct ASTDumpContext
         m_writer->dedent();
         m_writer->emit("}");
     }
-    void dump(const GlobalGenericParamSubstitution::ConstraintArg& arg)
-    {
-        m_writer->emit(" { \n");
-        m_writer->indent();
-
-        dump(arg.decl);
-        m_writer->emit(",\n");
-        dump(arg.val);
-        m_writer->emit("\n");
-
-        m_writer->dedent();
-        m_writer->emit("}");
-    }
     void dump(const TypeExp& exp)
     {
         m_writer->emit(" { \n");
diff --git a/source/slang/slang-ast-substitutions.cpp b/source/slang/slang-ast-substitutions.cpp
index acff8201e..6656f1fa6 100644
--- a/source/slang/slang-ast-substitutions.cpp
+++ b/source/slang/slang-ast-substitutions.cpp
@@ -163,75 +163,4 @@ HashCode ThisTypeSubstitution::_getHashCodeOverride() const
     return witness->getHashCode();
 }
 
-// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! GlobalGenericParamSubstitution !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-
-Substitutions* GlobalGenericParamSubstitution::_applySubstitutionsShallowOverride(ASTBuilder* astBuilder, SubstitutionSet substSet, Substitutions* substOuter, int* ioDiff)
-{
-    // if we find a GlobalGenericParamSubstitution in subst that references the same type_param decl
-    // return a copy of that GlobalGenericParamSubstitution
-    int diff = 0;
-
-    if (substOuter != outer) diff++;
-
-    auto substActualType = as<Type>(actualType->substituteImpl(astBuilder, substSet, &diff));
-
-    List<ConstraintArg> substConstraintArgs;
-    for (auto constraintArg : constraintArgs)
-    {
-        ConstraintArg substConstraintArg;
-        substConstraintArg.decl = constraintArg.decl;
-        substConstraintArg.val = constraintArg.val->substituteImpl(astBuilder, substSet, &diff);
-
-        substConstraintArgs.add(substConstraintArg);
-    }
-
-    if (!diff)
-        return this;
-
-    (*ioDiff)++;
-
-    GlobalGenericParamSubstitution* substSubst = astBuilder->create<GlobalGenericParamSubstitution>();
-    substSubst->paramDecl = paramDecl;
-    substSubst->actualType = substActualType;
-    substSubst->constraintArgs = substConstraintArgs;
-    substSubst->outer = substOuter;
-    return substSubst;
-}
-
-bool GlobalGenericParamSubstitution::_equalsOverride(Substitutions* subst)
-{
-    if (!subst)
-        return false;
-    if (subst == this)
-        return true;
-
-    if (auto genSubst = as<GlobalGenericParamSubstitution>(subst))
-    {
-        if (paramDecl != genSubst->paramDecl)
-            return false;
-        if (!actualType->equalsVal(genSubst->actualType))
-            return false;
-        if (constraintArgs.getCount() != genSubst->constraintArgs.getCount())
-            return false;
-        for (Index i = 0; i < constraintArgs.getCount(); i++)
-        {
-            if (!constraintArgs[i].val->equalsVal(genSubst->constraintArgs[i].val))
-                return false;
-        }
-        return true;
-    }
-    return false;
-}
-
-HashCode GlobalGenericParamSubstitution::_getHashCodeOverride() const
-{
-    HashCode rs = actualType->getHashCode();
-    for (auto && a : constraintArgs)
-    {
-        rs = combineHash(rs, a.val->getHashCode());
-    }
-    return rs;
-}
-
-
 } // namespace Slang
diff --git a/source/slang/slang-ast-type.cpp b/source/slang/slang-ast-type.cpp
index 2c2557233..9c00c13ba 100644
--- a/source/slang/slang-ast-type.cpp
+++ b/source/slang/slang-ast-type.cpp
@@ -219,22 +219,6 @@ Val* DeclRefType::_substituteImplOverride(ASTBuilder* astBuilder, SubstitutionSe
             }
         }
     }
-    else if (auto globalGenParam = as<GlobalGenericParamDecl>(declRef.getDecl()))
-    {
-        // search for a substitution that might apply to us
-        for (auto s = subst.substitutions; s; s = s->outer)
-        {
-            auto genericSubst = as<GlobalGenericParamSubstitution>(s);
-            if (!genericSubst)
-                continue;
-
-            if (genericSubst->paramDecl == globalGenParam)
-            {
-                (*ioDiff)++;
-                return genericSubst->actualType;
-            }
-        }
-    }
     int diff = 0;
     DeclRef<Decl> substDeclRef = declRef.substituteImpl(astBuilder, subst, &diff);
 
diff --git a/source/slang/slang-ast-val.cpp b/source/slang/slang-ast-val.cpp
index 7dbda6e86..5396749e5 100644
--- a/source/slang/slang-ast-val.cpp
+++ b/source/slang/slang-ast-val.cpp
@@ -258,21 +258,6 @@ Val* DeclaredSubtypeWitness::_substituteImplOverride(ASTBuilder* astBuilder, Sub
                     return genericSubst->args[index + ordinaryParamCount];
                 }
             }
-            else if (auto globalGenericSubst = as<GlobalGenericParamSubstitution>(s))
-            {
-                // check if the substitution is really about this global generic type parameter
-                if (globalGenericSubst->paramDecl != genConstraintDecl->parentDecl)
-                    continue;
-
-                for (auto constraintArg : globalGenericSubst->constraintArgs)
-                {
-                    if (constraintArg.decl != genConstraintDecl)
-                        continue;
-
-                    (*ioDiff)++;
-                    return constraintArg.val;
-                }
-            }
         }
     }
 
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 1ea3c71fb..06e463d7d 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -7339,11 +7339,6 @@ LoweredValInfo emitDeclRef(
     // We need to proceed by considering the specializations that
     // have been put in place.
 
-    // Ignore any global generic type substitutions during lowering.
-    // Really, we don't even expect these to appear.
-    while(auto globalGenericSubst = as<GlobalGenericParamSubstitution>(subst))
-        subst = globalGenericSubst->outer;
-
     // If the declaration would not get wrapped in a `IRGeneric`,
     // even if it is nested inside of an AST `GenericDecl`, then
     // we should also ignore any generic substitutions.
diff --git a/source/slang/slang-serialize-ast-type-info.h b/source/slang/slang-serialize-ast-type-info.h
index 400474046..937ecc95f 100644
--- a/source/slang/slang-serialize-ast-type-info.h
+++ b/source/slang/slang-serialize-ast-type-info.h
@@ -144,9 +144,6 @@ struct SerialTypeInfo<LookupResult>
     }
 };
 
-// GlobalGenericParamSubstitution::ConstraintArg
-SLANG_VALUE_TYPE_INFO(GlobalGenericParamSubstitution_ConstraintArg)
-
 // SpecializationArg
 SLANG_VALUE_TYPE_INFO(SpecializationArg)
 // ExpandedSpecializationArg
diff --git a/source/slang/slang-syntax.cpp b/source/slang/slang-syntax.cpp
index 82e94fb6a..d6e966aaa 100644
--- a/source/slang/slang-syntax.cpp
+++ b/source/slang/slang-syntax.cpp
@@ -667,25 +667,6 @@ Index getFilterCountImpl(const ReflectClassInfo& clsInfo, MemberFilterStyle filt
         return nullptr;
     }
 
-    GlobalGenericParamSubstitution* findGlobalGenericSubst(
-        Substitutions*   substs,
-        GlobalGenericParamDecl* paramDecl)
-    {
-        for(auto s = substs; s; s = s->outer)
-        {
-            auto gSubst = as<GlobalGenericParamSubstitution>(s);
-            if(!gSubst)
-                continue;
-
-            if(gSubst->paramDecl != paramDecl)
-                continue;
-
-            return gSubst;
-        }
-
-        return nullptr;
-    }
-
     Substitutions* specializeSubstitutionsShallow(
         ASTBuilder*             astBuilder, 
         Substitutions*   substToSpecialize,
@@ -697,105 +678,6 @@ Index getFilterCountImpl(const ReflectClassInfo& clsInfo, MemberFilterStyle filt
         return substToSpecialize->applySubstitutionsShallow(astBuilder, substsToApply, restSubst, ioDiff);
     }
 
-    Substitutions* specializeGlobalGenericSubstitutions(
-        ASTBuilder*                         astBuilder,
-        Decl*                               declToSpecialize,
-        Substitutions*               substsToSpecialize,
-        Substitutions*               substsToApply,
-        int*                                ioDiff,
-        HashSet<GlobalGenericParamDecl*>&   ioParametersFound)
-    {
-        // Any existing global-generic substitutions will trigger
-        // a recursive case that skips the rest of the function.
-        for(auto specSubst = substsToSpecialize; specSubst; specSubst = specSubst->outer)
-        {
-            auto specGlobalGenericSubst = as<GlobalGenericParamSubstitution>(specSubst);
-            if(!specGlobalGenericSubst)
-                continue;
-
-            ioParametersFound.Add(specGlobalGenericSubst->paramDecl);
-
-            int diff = 0;
-            auto restSubst = specializeGlobalGenericSubstitutions(
-                astBuilder,
-                declToSpecialize,
-                specSubst->outer,
-                substsToApply,
-                &diff,
-                ioParametersFound);
-
-            auto firstSubst = specializeSubstitutionsShallow(
-                astBuilder,
-                specGlobalGenericSubst,
-                substsToApply,
-                restSubst,
-                &diff);
-
-            *ioDiff += diff;
-            return firstSubst;
-        }
-
-        // No more existing substitutions, so we know we can apply
-        // our global generic substitutions without any special work.
-
-        // We expect global generic substitutions to come at
-        // the end of the list in all cases, so lets advance
-        // until we see them.
-        Substitutions* appGlobalGenericSubsts = substsToApply;
-        while(appGlobalGenericSubsts && !as<GlobalGenericParamSubstitution>(appGlobalGenericSubsts))
-            appGlobalGenericSubsts = appGlobalGenericSubsts->outer;
-
-
-        // If there is nothing to apply, then we are done
-        if(!appGlobalGenericSubsts)
-            return nullptr;
-
-        // Otherwise, it seems like something has to change.
-        (*ioDiff)++;
-
-        // If there were no parameters bound by the existing substitution,
-        // then we can safely use the global generics from the to-apply set.
-        if(ioParametersFound.Count() == 0)
-            return appGlobalGenericSubsts;
-
-        Substitutions* resultSubst = nullptr;
-        Substitutions** link = &resultSubst;
-        for(auto appSubst = appGlobalGenericSubsts; appSubst; appSubst = appSubst->outer)
-        {
-            auto appGlobalGenericSubst = as<GlobalGenericParamSubstitution>(appSubst);
-            if(!appSubst)
-                continue;
-
-            // Don't include substitutions for parameters already handled.
-            if(ioParametersFound.Contains(appGlobalGenericSubst->paramDecl))
-                continue;
-
-            GlobalGenericParamSubstitution* newSubst = astBuilder->create<GlobalGenericParamSubstitution>();
-            newSubst->paramDecl = appGlobalGenericSubst->paramDecl;
-            newSubst->actualType = appGlobalGenericSubst->actualType;
-            newSubst->constraintArgs = appGlobalGenericSubst->constraintArgs;
-
-            *link = newSubst;
-            link = &newSubst->outer;
-        }
-
-        return resultSubst;
-    }
-
-    Substitutions* specializeGlobalGenericSubstitutions(
-        ASTBuilder*             astBuilder,
-        Decl*                   declToSpecialize,
-        Substitutions*   substsToSpecialize,
-        Substitutions*   substsToApply,
-        int*                    ioDiff)
-    {
-        // Keep track of any parameters already present in the
-        // existing substitution.
-        HashSet<GlobalGenericParamDecl*> parametersFound;
-        return specializeGlobalGenericSubstitutions(astBuilder, declToSpecialize, substsToSpecialize, substsToApply, ioDiff, parametersFound);
-    }
-
-
     // Construct new substitutions to apply to a declaration,
     // based on a provided substitution set to be applied
     Substitutions* specializeSubstitutions(
@@ -965,21 +847,11 @@ Index getFilterCountImpl(const ReflectClassInfo& clsInfo, MemberFilterStyle filt
         // would be specializations that don't actually apply to the given
         // declaration.
         //
-        // The remaining substitutions to apply, if any, should thus be
-        // global-generic substitutions. And similarly, those are the
-        // only remaining substitutions we really care about in
-        // `substsToApply`.
-        //
         // Note: this does *not* mean that `substsToApply` doesn't have
         // any generic or this-type substitutions; it just means that none
         // of them were applicable.
         //
-        return specializeGlobalGenericSubstitutions(
-            astBuilder,
-            declToSpecialize,
-            substsToSpecialize,
-            substsToApply,
-            ioDiff);
+        return nullptr;
     }
 
     DeclRefBase DeclRefBase::substituteImpl(ASTBuilder* astBuilder, SubstitutionSet substSet, int* ioDiff)