[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
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 42411c9..0daa33c 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -206,6 +206,7 @@
case DefiningSynthesizedFunction:
case ExceptionSpecEvaluation:
case ConstraintSubstitution:
+ case RewritingOperatorAsSpaceship:
return false;
// This function should never be called when Kind's value is Memoization.
@@ -682,6 +683,11 @@
break;
}
+ case CodeSynthesisContext::RewritingOperatorAsSpaceship:
+ Diags.Report(Active->Entity->getLocation(),
+ diag::note_rewriting_operator_as_spaceship);
+ break;
+
case CodeSynthesisContext::Memoization:
break;
@@ -754,6 +760,7 @@
case CodeSynthesisContext::DeclaringSpecialMember:
case CodeSynthesisContext::DefiningSynthesizedFunction:
+ case CodeSynthesisContext::RewritingOperatorAsSpaceship:
// This happens in a context unrelated to template instantiation, so
// there is no SFINAE.
return None;