[NFC] Add implicit cast kinds for function pointer conversions

The new cast kinds are needed to distinguish between no-op conversions
and conversions from pointers to noexcept functions to pointers to
functions without noexcept as the latter can cause function pointers to
be re-signed on arm64e.

See #109056 for background.

Author: ahatanak

clang-tools-extra/clang-tidy/bugprone/SwappedArgumentsCheck.cpp

@@ -27,6 +27,8 @@ void SwappedArgumentsCheck::registerMatchers(MatchFinder *Finder) {
 static const Expr *ignoreNoOpCasts(const Expr *E) {
   if (auto *Cast = dyn_cast<CastExpr>(E))
     if (Cast->getCastKind() == CK_LValueToRValue ||
+        Cast->getCastKind() == CK_FunctionPointerConversion ||
+        Cast->getCastKind() == CK_MemberFunctionPointerConversion ||
         Cast->getCastKind() == CK_NoOp)
       return ignoreNoOpCasts(Cast->getSubExpr());
   return E;

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.cpp

@@ -90,7 +90,9 @@ void ProTypeCstyleCastCheck::check(const MatchFinder::MatchResult &Result) {
     return;
   }
 
-  if (MatchedCast->getCastKind() == CK_NoOp &&
+  if ((MatchedCast->getCastKind() == CK_NoOp ||
+       MatchedCast->getCastKind() == CK_FunctionPointerConversion ||
+       MatchedCast->getCastKind() == CK_MemberFunctionPointerConversion) &&
       needsConstCast(SourceType, MatchedCast->getType())) {
     diag(MatchedCast->getBeginLoc(),
          "do not use C-style cast to cast away constness");

clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp

@@ -123,7 +123,10 @@ void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
       DestTypeAsWritten->isRecordType() &&
       !DestTypeAsWritten->isElaboratedTypeSpecifier();
 
-  if (CastExpr->getCastKind() == CK_NoOp && !FnToFnCast) {
+  if ((CastExpr->getCastKind() == CK_NoOp ||
+       CastExpr->getCastKind() == CK_FunctionPointerConversion ||
+       CastExpr->getCastKind() == CK_MemberFunctionPointerConversion) &&
+      !FnToFnCast) {
     // Function pointer/reference casts may be needed to resolve ambiguities in
     // case of overloaded functions, so detection of redundant casts is trickier
     // in this case. Don't emit "redundant cast" warnings for function
@@ -201,6 +204,8 @@ void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
     }
     return;
   case CK_NoOp:
+  case CK_FunctionPointerConversion:
+  case CK_MemberFunctionPointerConversion:
     if (FnToFnCast) {
       ReplaceWithNamedCast("static_cast");
       return;

clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp

@@ -500,7 +500,9 @@ static bool canBeModified(ASTContext *Context, const Expr *E) {
   if (Parents.size() != 1)
     return true;
   if (const auto *Cast = Parents[0].get<ImplicitCastExpr>()) {
-    if ((Cast->getCastKind() == CK_NoOp &&
+    if (((Cast->getCastKind() == CK_NoOp ||
+          Cast->getCastKind() == CK_FunctionPointerConversion ||
+          Cast->getCastKind() == CK_MemberFunctionPointerConversion) &&
          Context->hasSameType(Cast->getType(), E->getType().withConst())) ||
         (Cast->getCastKind() == CK_LValueToRValue &&
          !Cast->getType().isNull() && Cast->getType()->isFundamentalType()))

clang-tools-extra/clang-tidy/performance/ImplicitConversionInLoopCheck.cpp

@@ -24,7 +24,9 @@ namespace clang::tidy::performance {
 // case we skip the first cast expr.
 static bool isNonTrivialImplicitCast(const Stmt *ST) {
   if (const auto *ICE = dyn_cast<ImplicitCastExpr>(ST)) {
-    return (ICE->getCastKind() != CK_NoOp) ||
+    return (ICE->getCastKind() != CK_NoOp &&
+            ICE->getCastKind() != CK_FunctionPointerConversion &&
+            ICE->getCastKind() != CK_MemberFunctionPointerConversion) ||
            isNonTrivialImplicitCast(ICE->getSubExpr());
   }
   return false;

clang-tools-extra/clang-tidy/readability/MakeMemberFunctionConstCheck.cpp

@@ -97,7 +97,9 @@ class FindUsageOfThis : public RecursiveASTVisitor<FindUsageOfThis> {
   //  (possibly `-UnaryOperator Deref)
   //        `-CXXThisExpr 'S *' this
   bool visitUser(const ImplicitCastExpr *Cast) {
-    if (Cast->getCastKind() != CK_NoOp)
+    if (Cast->getCastKind() != CK_NoOp &&
+        Cast->getCastKind() != CK_FunctionPointerConversion &&
+        Cast->getCastKind() != CK_MemberFunctionPointerConversion)
       return false; // Stop traversal.
 
     // Only allow NoOp cast to 'const S' or 'const S *'.
@@ -159,7 +161,10 @@ class FindUsageOfThis : public RecursiveASTVisitor<FindUsageOfThis> {
       if (Cast->getCastKind() == CK_LValueToRValue)
         return true;
 
-      if (Cast->getCastKind() == CK_NoOp && Cast->getType().isConstQualified())
+      if ((Cast->getCastKind() == CK_NoOp ||
+           Cast->getCastKind() == CK_FunctionPointerConversion ||
+           Cast->getCastKind() == CK_MemberFunctionPointerConversion) &&
+          Cast->getType().isConstQualified())
         return true;
     }
 

clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp

@@ -240,6 +240,8 @@ AST_MATCHER_P(DeclRefExpr, doesNotMutateObject, int, Indirections) {
         case CK_BaseToDerived:
         case CK_DerivedToBase:
         case CK_UncheckedDerivedToBase:
+        case CK_FunctionPointerConversion:
+        case CK_MemberFunctionPointerConversion:
         case CK_Dynamic:
         case CK_BaseToDerivedMemberPointer:
         case CK_DerivedToBaseMemberPointer:

clang-tools-extra/clangd/Hover.cpp

@@ -1118,6 +1118,8 @@ void maybeAddCalleeArgInfo(const SelectionTree::Node *N, HoverInfo &HI,
     if (const auto *ImplicitCast = CastNode->ASTNode.get<ImplicitCastExpr>()) {
       switch (ImplicitCast->getCastKind()) {
       case CK_NoOp:
+      case CK_FunctionPointerConversion:
+      case CK_MemberFunctionPointerConversion:
       case CK_DerivedToBase:
       case CK_UncheckedDerivedToBase:
         // If it was a reference before, it's still a reference.

clang/include/clang/AST/IgnoreExpr.h

@@ -102,7 +102,9 @@ inline Expr *IgnoreBaseCastsSingleStep(Expr *E) {
   if (auto *CE = dyn_cast<CastExpr>(E))
     if (CE->getCastKind() == CK_DerivedToBase ||
         CE->getCastKind() == CK_UncheckedDerivedToBase ||
-        CE->getCastKind() == CK_NoOp)
+        CE->getCastKind() == CK_NoOp ||
+        CE->getCastKind() == CK_FunctionPointerConversion ||
+        CE->getCastKind() == CK_MemberFunctionPointerConversion)
       return CE->getSubExpr();
 
   return E;

clang/include/clang/AST/OperationKinds.def

@@ -84,6 +84,14 @@ CAST_OPERATION(LValueToRValue)
 ///   void () noexcept -> void ()
 CAST_OPERATION(NoOp)
 
+/// CK_FunctionPointerConversion - A conversion from pointer/reference to
+/// noexcept function to pointer/reference to function.
+CAST_OPERATION(FunctionPointerConversion)
+
+/// CK_MemberFunctionPointerConversion - A conversion from pointer to noexcept
+/// member function to pointer to member function.
+CAST_OPERATION(MemberFunctionPointerConversion)
+
 /// CK_BaseToDerived - A conversion from a C++ class pointer/reference
 /// to a derived class pointer/reference.
 ///   B *b = static_cast<B*>(a);