[C++2a] Implement operator<=> CodeGen and ExprConstant

Summary:
This patch tackles long hanging fruit for the builtin operator<=> expressions. It is currently needs some cleanup before landing, but I want to get some initial feedback.

The main changes are:

* Lookup, build, and store the required standard library types and expressions in `ASTContext`. By storing them in ASTContext we don't need to store (and duplicate) the required expressions in the BinaryOperator AST nodes. 

* Implement [expr.spaceship] checking, including diagnosing narrowing conversions. 

* Implement `ExprConstant` for builtin spaceship operators.

* Implement builitin operator<=> support in `CodeGenAgg`. Initially I emitted the required comparisons using `ScalarExprEmitter::VisitBinaryOperator`, but this caused the operand expressions to be emitted once for every required cmp.

* Implement [builtin.over] with modifications to support the intent of P0946R0. See the note on `BuiltinOperatorOverloadBuilder::addThreeWayArithmeticOverloads` for more information about the workaround.




Reviewers: rsmith, aaron.ballman, majnemer, rnk, compnerd, rjmccall

Reviewed By: rjmccall

Subscribers: rjmccall, rsmith, aaron.ballman, junbuml, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D45476

llvm-svn: 331677

1 files changed, 7 insertions, 4 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 5c0026cd374..b964cb2f0ef 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -137,10 +137,13 @@ Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
       ValueWithBytesObjCTypeMethod(nullptr), NSArrayDecl(nullptr),
       ArrayWithObjectsMethod(nullptr), NSDictionaryDecl(nullptr),
       DictionaryWithObjectsMethod(nullptr), GlobalNewDeleteDeclared(false),
-      TUKind(TUKind), NumSFINAEErrors(0), AccessCheckingSFINAE(false),
-      InNonInstantiationSFINAEContext(false), NonInstantiationEntries(0),
-      ArgumentPackSubstitutionIndex(-1), CurrentInstantiationScope(nullptr),
-      DisableTypoCorrection(false), TyposCorrected(0), AnalysisWarnings(*this),
+      TUKind(TUKind), NumSFINAEErrors(0),
+      FullyCheckedComparisonCategories(
+          static_cast<unsigned>(ComparisonCategoryType::Last) + 1),
+      AccessCheckingSFINAE(false), InNonInstantiationSFINAEContext(false),
+      NonInstantiationEntries(0), ArgumentPackSubstitutionIndex(-1),
+      CurrentInstantiationScope(nullptr), DisableTypoCorrection(false),
+      TyposCorrected(0), AnalysisWarnings(*this),
       ThreadSafetyDeclCache(nullptr), VarDataSharingAttributesStack(nullptr),
       CurScope(nullptr), Ident_super(nullptr), Ident___float128(nullptr) {
   TUScope = nullptr;