[c++20] Add rewriting from comparison operators to <=> / ==.

This adds support for rewriting <, >, <=, and >= to a normal or reversed
call to operator<=>, for rewriting != to a normal or reversed call to
operator==, and for rewriting <=> and == to reversed forms of those same
operators.

Note that this is a breaking change for various C++17 code patterns,
including some in use in LLVM. The most common patterns (where an
operator== becomes ambiguous with a reversed form of itself) are still
accepted under this patch, as an extension (with a warning). I'm hopeful
that we can get the language rules fixed before C++20 ships, and the
extension warning is aimed primarily at providing data to inform that
decision.

llvm-svn: 375306

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 09cc525837c..3f2d38630c3 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -24,6 +24,7 @@
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/Lookup.h"
+#include "clang/Sema/Overload.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaInternal.h"
@@ -8488,7 +8489,7 @@ bool Sema::CheckFunctionTemplateSpecialization(
     // candidates at once, to get proper sorting and limiting.
     for (auto *OldND : Previous) {
       if (auto *OldFD = dyn_cast<FunctionDecl>(OldND->getUnderlyingDecl()))
-        NoteOverloadCandidate(OldND, OldFD, FD->getType(), false);
+        NoteOverloadCandidate(OldND, OldFD, CRK_None, FD->getType(), false);
     }
     FailedCandidates.NoteCandidates(*this, FD->getLocation());
     return true;