[clang] Add __has_extension(swiftcc) support

This patch adds `swiftcc` extension to check if the target supports Swift
calling convention as well as we do for `swiftasynccc`.
Also `swiftasynccc` is now considered to be a Clang extension rather than a
language standard feature to reflect the nature of the attribute.

Author: kateinoigakukun

clang/docs/ReleaseNotes.rst

@@ -215,6 +215,12 @@ for the full list.
 
   This allows the ``_Nullable`` and ``_Nonnull` family of type attributes to
   apply to this class.
+- The ``swiftasynccc`` attribute is now considered to be a Clang extension
+  rather than a language standard feature. Please use
+  ``__has_extension(swiftasynccc)`` to check the availability of this attribute
+  for the target platform instead of ``__has_feature(swiftasynccc)``. Also,
+  added a new extension query ``__has_extension(swiftcc)`` corresponding to the
+  ``__attribute__((swiftcc))`` attribute.
 
 Improvements to Clang's diagnostics
 -----------------------------------

clang/include/clang/Basic/AttrDocs.td

@@ -5162,10 +5162,11 @@ that does not. A single parameter may not have multiple ABI treatment
 attributes.
 
 Support for this feature is target-dependent, although it should be
-supported on every target that Swift supports. Query for this support
-with ``__has_attribute(swiftcall)``. This implies support for the
-``swift_context``, ``swift_error_result``, and ``swift_indirect_result``
-attributes.
+supported on every target that Swift supports. Query for this attribute
+with ``__has_attribute(swiftcall)``. Query if the target supports the
+calling convention with ``__has_extension(swiftcc)``. This implies
+support for the ``swift_context``, ``swift_error_result``, and
+``swift_indirect_result`` attributes.
   }];
 }
 
@@ -5212,6 +5213,10 @@ the following:
   semantically be performed after a guaranteed tail call, such as the
   non-trivial destruction of a local variable or temporary,
   then the program is ill-formed.
+
+Query for this attribute with ``__has_attribute(swiftasynccall)``. Query if
+the target supports the calling convention with
+``__has_extension(swiftasynccc)``.
   }];
 }
 

clang/include/clang/Basic/Features.def

@@ -102,7 +102,10 @@ FEATURE(memory_sanitizer,
 FEATURE(thread_sanitizer, LangOpts.Sanitize.has(SanitizerKind::Thread))
 FEATURE(dataflow_sanitizer, LangOpts.Sanitize.has(SanitizerKind::DataFlow))
 FEATURE(scudo, LangOpts.Sanitize.hasOneOf(SanitizerKind::Scudo))
-FEATURE(swiftasynccc,
+EXTENSION(swiftcc,
+  PP.getTargetInfo().checkCallingConvention(CC_Swift) ==
+  clang::TargetInfo::CCCR_OK)
+EXTENSION(swiftasynccc,
   PP.getTargetInfo().checkCallingConvention(CC_SwiftAsync) ==
   clang::TargetInfo::CCCR_OK)
 FEATURE(pragma_stdc_cx_limited_range, true)

clang/test/Sema/swift-call-conv.c

@@ -1,7 +1,12 @@
 // RUN: %clang_cc1 -triple aarch64-unknown-windows-msvc -fsyntax-only %s -verify
 // RUN: %clang_cc1 -triple thumbv7-unknown-windows-msvc -fsyntax-only %s -verify
 // RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -fsyntax-only %s -verify
+// RISC-V does not support swiftcall
+// RUN: %clang_cc1 -triple riscv32-unknown-elf -fsyntax-only %s -verify
 
+#if __has_extension(swiftcc)
 // expected-no-diagnostics
-
+#else
+// expected-warning@+2 {{'__swiftcall__' calling convention is not supported for this target}}
+#endif
 void __attribute__((__swiftcall__)) f(void) {}