[Builtins] Overload __builtin_operator_new/delete to allow forwarding to usual allocation/deallocation functions.

Summary:
Libc++'s default allocator uses `__builtin_operator_new` and `__builtin_operator_delete` in order to allow the calls to new/delete to be ellided. However, libc++ now needs to support over-aligned types in the default allocator. In order to support this without disabling the existing optimization Clang needs to support calling the aligned new overloads from the builtins.

See llvm.org/PR22634 for more information about the libc++ bug.

This patch changes `__builtin_operator_new`/`__builtin_operator_delete` to call any usual `operator new`/`operator delete` function. It does this by performing overload resolution with the arguments passed to the builtin to determine which allocation function to call. If the selected function is not a usual allocation function a diagnostic is issued.

One open issue is if the `align_val_t` overloads should be considered "usual" when `LangOpts::AlignedAllocation` is disabled.


In order to allow libc++ to detect this new behavior the value for `__has_builtin(__builtin_operator_new)` has been updated to `201802`.

Reviewers: rsmith, majnemer, aaron.ballman, erik.pilkington, bogner, ahatanak

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D43047

llvm-svn: 328134

1 files changed, 12 insertions, 3 deletions

diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 7f524c5591c..6ab737d15c8 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1801,12 +1801,21 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
       [this](Token &Tok, bool &HasLexedNextToken) -> int {
         IdentifierInfo *II = ExpectFeatureIdentifierInfo(Tok, *this,
                                            diag::err_feature_check_malformed);
+        const LangOptions &LangOpts = getLangOpts();
         if (!II)
           return false;
-        else if (II->getBuiltinID() != 0)
+        else if (II->getBuiltinID() != 0) {
+          switch (II->getBuiltinID()) {
+          case Builtin::BI__builtin_operator_new:
+          case Builtin::BI__builtin_operator_delete:
+            // denotes date of behavior change to support calling arbitrary
+            // usual allocation and deallocation functions. Required by libc++
+            return 201802;
+          default:
+            return true;
+          }
           return true;
-        else {
-          const LangOptions &LangOpts = getLangOpts();
+        } else {
           return llvm::StringSwitch<bool>(II->getName())
                       .Case("__make_integer_seq", LangOpts.CPlusPlus)
                       .Case("__type_pack_element", LangOpts.CPlusPlus)