[clang][bytecode] Fix three-way unordered non-pointer comparisions (llvm#127759)

This _can_ happen with non-pointers, but we shouldn't diagnose it in
that case.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -1132,13 +1132,14 @@ bool CMP3(InterpState &S, CodePtr OpPC, const ComparisonCategoryInfo *CmpInfo) {
   const Pointer &P = S.Stk.peek<Pointer>();
 
   ComparisonCategoryResult CmpResult = LHS.compare(RHS);
-  if (CmpResult == ComparisonCategoryResult::Unordered) {
-    // This should only happen with pointers.
-    const SourceInfo &Loc = S.Current->getSource(OpPC);
-    S.FFDiag(Loc, diag::note_constexpr_pointer_comparison_unspecified)
-        << LHS.toDiagnosticString(S.getASTContext())
-        << RHS.toDiagnosticString(S.getASTContext());
-    return false;
+  if constexpr (std::is_same_v<T, Pointer>) {
+    if (CmpResult == ComparisonCategoryResult::Unordered) {
+      const SourceInfo &Loc = S.Current->getSource(OpPC);
+      S.FFDiag(Loc, diag::note_constexpr_pointer_comparison_unspecified)
+          << LHS.toDiagnosticString(S.getASTContext())
+          << RHS.toDiagnosticString(S.getASTContext());
+      return false;
+    }
   }
 
   assert(CmpInfo);

clang/test/AST/ByteCode/cxx20.cpp

@@ -626,6 +626,8 @@ namespace ThreeWayCmp {
   constexpr int k = (1 <=> 1, 0); // both-warning {{comparison result unused}}
   static_assert(k== 0, "");
 
+  static_assert(__builtin_nanf("") <=> __builtin_nanf("") == -127, "");
+
   /// Pointers.
   constexpr int a[] = {1,2,3};
   constexpr int b[] = {1,2,3};