[clang] NFC: introduce UnsignedOrNone as a replacement for std::optional<unsigned> (#134142)

This introduces a new class 'UnsignedOrNone', which models a lite
version of `std::optional<unsigned>`, but has the same size as
'unsigned'.

This replaces most uses of `std::optional<unsigned>`, and similar
schemes utilizing 'int' and '-1' as sentinel.

Besides the smaller size advantage, this is simpler to serialize, as its
internal representation is a single unsigned int as well.

1 files changed, 7 insertions, 9 deletions

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index e10c492..011a6d0 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -289,7 +289,7 @@ static ExprResult EvaluateAtomicConstraint(
   return SubstitutedExpression;
 }
 
-std::optional<unsigned> static EvaluateFoldExpandedConstraintSize(
+static UnsignedOrNone EvaluateFoldExpandedConstraintSize(
     Sema &S, const CXXFoldExpr *FE, const NamedDecl *Template,
     SourceLocation TemplateNameLoc, const MultiLevelTemplateArgumentList &MLTAL,
     ConstraintSatisfaction &Satisfaction) {
@@ -304,15 +304,14 @@ std::optional<unsigned> static EvaluateFoldExpandedConstraintSize(
   assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");
   bool Expand = true;
   bool RetainExpansion = false;
-  std::optional<unsigned> OrigNumExpansions = FE->getNumExpansions(),
-                          NumExpansions = OrigNumExpansions;
+  UnsignedOrNone NumExpansions = FE->getNumExpansions();
   if (S.CheckParameterPacksForExpansion(
           FE->getEllipsisLoc(), Pattern->getSourceRange(), Unexpanded, MLTAL,
           Expand, RetainExpansion, NumExpansions) ||
       !Expand || RetainExpansion)
     return std::nullopt;
 
-  if (NumExpansions && S.getLangOpts().BracketDepth < NumExpansions) {
+  if (NumExpansions && S.getLangOpts().BracketDepth < *NumExpansions) {
     S.Diag(FE->getEllipsisLoc(),
            clang::diag::err_fold_expression_limit_exceeded)
         << *NumExpansions << S.getLangOpts().BracketDepth
@@ -413,12 +412,12 @@ static ExprResult calculateConstraintSatisfaction(
     if (Conjunction != Satisfaction.IsSatisfied)
       return Out;
   }
-  std::optional<unsigned> NumExpansions = EvaluateFoldExpandedConstraintSize(
+  UnsignedOrNone NumExpansions = EvaluateFoldExpandedConstraintSize(
       S, FE, Template, TemplateNameLoc, MLTAL, Satisfaction);
   if (!NumExpansions)
     return ExprError();
   for (unsigned I = 0; I < *NumExpansions; I++) {
-    Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, I);
+    Sema::ArgPackSubstIndexRAII SubstIndex(S, I);
     ExprResult Res = calculateConstraintSatisfaction(
         S, FE->getPattern(), Template, TemplateNameLoc, MLTAL, Satisfaction);
     if (Res.isInvalid())
@@ -589,8 +588,7 @@ static bool CheckConstraintSatisfaction(
     return true;
 
   for (const AssociatedConstraint &AC : AssociatedConstraints) {
-    Sema::ArgumentPackSubstitutionIndexRAII _(S,
-                                              AC.ArgumentPackSubstitutionIndex);
+    Sema::ArgPackSubstIndexRAII _(S, AC.ArgPackSubstIndex);
     ExprResult Res = calculateConstraintSatisfaction(
         S, Template, TemplateIDRange.getBegin(), TemplateArgsLists,
         AC.ConstraintExpr, Satisfaction);
@@ -1406,7 +1404,7 @@ substituteParameterMappings(Sema &S, NormalizedConstraint &N,
   }
 
   if (N.isFoldExpanded()) {
-    Sema::ArgumentPackSubstitutionIndexRAII _(S, -1);
+    Sema::ArgPackSubstIndexRAII _(S, std::nullopt);
     return substituteParameterMappings(
         S, N.getFoldExpandedConstraint()->Constraint, Concept, MLTAL,
         ArgsAsWritten);