[Clang] Introduce Swift async calling convention.

[varungandhi-apple]

Summary

This change is intended as initial setup. The plan is to add
more semantic checks later. I plan to update the documentation
as more semantic checks are added (instead of documenting the
details up front). Most of the code closely mirrors that for
the Swift calling convention. Three places are marked as
[FIXME: swiftasynccc]; those will be addressed once the
corresponding convention is introduced in LLVM.

[varungandhi-apple]

clang/include/clang/Basic/AttrDocs.td

4398

I have left this as a TODO for now, so that it can be filled in later when the exact details of the convention are implemented in LLVM.

[varungandhi-apple]

I don't get how you stack your change on top of someone else's change (the diff seems to have been created with only one commit), but this depends on https://reviews.llvm.org/D95228, which depends on https://reviews.llvm.org/D95044.

[dexonsmith]

In D95561#2526417, @varungandhi-apple wrote:

I don't get how you stack your change on top of someone else's change (the diff seems to have been created with only one commit), but this depends on https://reviews.llvm.org/D95228, which depends on https://reviews.llvm.org/D95044.

You should be able to click the "Edit Related Revisions" link in the top right, click "Parent", and search for / select "D95228".

[varungandhi-apple]

clang/lib/AST/MicrosoftMangle.cpp

2688–2689

Whitespace needs fixing after comment was broken up by arc's linter.

llvm/lib/Demangle/MicrosoftDemangleNodes.cpp

114

Need to add extra whitespace at end similar to __swiftcall__.

llvm/test/Demangle/ms-mangle.test

345

[rjmccall]

Broadly LGTM

clang/include/clang/Basic/AttrDocs.td

4398

We don't generally put precise CC details in this kind of documentation; the goal is to describe the calling convention at a high level. Here, you should describe it as being compatible with the low-level conventions of Swift async functions, provided it declares the right formal arguments. You should also talk about the special-case treatment of tail calls, especially the extension which adds return (void) to all language modes.

clang/lib/AST/MicrosoftMangle.cpp

2711

Please use consistent formatting with the other cases, here and elsewhere. Keeping the switch compact is better for readability than following an abstract style rule.

[varungandhi-apple]

clang/lib/Sema/SemaDeclAttr.cpp

8106–8115

There seems to be some weirdness here in handleCallConvAttr where the codepath to attach the attribute to the decl isn't taken. Instead in my examples, it exits out at this line:

if (hasDeclarator(D)) return;

with an isa<DeclaratorDecl> check.

[varungandhi-apple]

clang/lib/AST/MicrosoftMangle.cpp

2711

I'm pretty sure I wrote it the right way originally, but saying yes to the clang-tidy prompt by arc broke it. :sigh:

[rjmccall]

clang/lib/Sema/SemaDeclAttr.cpp

8106–8115

It doesn't need to be attached to the decl; it should be reflected in the type, the same as the other calling conventions. You would need it on the decl for something like an ObjC method.

[varungandhi-apple]

1. Update whitespace and add documentation for swiftasynccall.
2. Update commit message.

[rjmccall]

clang/include/clang/Basic/AttrDocs.td

4409

I don't think the "must be in tail position" here is true. Allow me to suggest an alternative way of saying this:

Within a swiftasynccall function, a call to a swiftasynccall function that is the immediate operand of a return statement is guaranteed to be performed as a tail call. This syntax is allowed even in C as an extension (a call to a void-returning function cannot be a return operand in standard C). If something in the calling function would 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.

[varungandhi-apple]

Correct documentation on tail call behavior as pointed out by John.

[varungandhi-apple]

clang/test/CodeGen/debug-info-cc.c

60–66

This needs to be changed in some way, it triggers a test failure in its current state. https://github.com/apple/llvm-project/pull/2444

[varungandhi-apple]

Fix test case for debuginfo.

[varungandhi-apple]

• Remove semantic restriction of swift_async_context being only applicable to swiftasynccall.
• Update target checks to make sure we only allow supported targets.
• Update doc comment.

[rjmccall]

LGTM other than the TargetInfo thing.

clang/include/clang/Basic/TargetInfo.h

1424 ↗

(On Diff #324389)

As I commented in the other patch, I think this would be cleaner in the long term if you just implemented it directly in the various target subclasses.

[varungandhi-apple]

Address review feedback; remove centralized target check for CC_SwiftAsync.

[rjmccall]

LGTM

[varungandhi-apple]

Permit swift_context and swift_indirect_result parameters for
swiftasynccall functions. (Earlier, these were restricted to
swiftcall-only.)

[varungandhi-apple]

Combined D95984 into this patch since all necessary LLVM patches have landed, so having the patches separated out is not helpful. Leaving this up for a few days in case there are any final comments before landing.

clang/include/clang-c/Index.h

  * The version constants for the libclang API.
  * CINDEX_VERSION_MINOR should increase when there are API additions.
  * CINDEX_VERSION_MAJOR is intended for "major" source/ABI breaking changes.
  *
  * The policy about the libclang API was always to keep it source and ABI
  * compatible, thus CINDEX_VERSION_MAJOR is expected to remain stable.
  */
 #define CINDEX_VERSION_MAJOR 0
-#define CINDEX_VERSION_MINOR 61
+#define CINDEX_VERSION_MINOR 62
 
 #define CINDEX_VERSION_ENCODE(major, minor) (((major)*10000) + ((minor)*1))
 
 #define CINDEX_VERSION                                                         \
   CINDEX_VERSION_ENCODE(CINDEX_VERSION_MAJOR, CINDEX_VERSION_MINOR)
 
 #define CINDEX_VERSION_STRINGIZE_(major, minor) #major "." #minor
 #define CINDEX_VERSION_STRINGIZE(major, minor)                                 \
enum CXCallingConv {
   /* Alias for compatibility with older versions of API. */
   CXCallingConv_X86_64Win64 = CXCallingConv_Win64,
   CXCallingConv_X86_64SysV = 11,
   CXCallingConv_X86VectorCall = 12,
   CXCallingConv_Swift = 13,
   CXCallingConv_PreserveMost = 14,
   CXCallingConv_PreserveAll = 15,
   CXCallingConv_AArch64VectorCall = 16,
+  CXCallingConv_SwiftAsync = 17,
 
   CXCallingConv_Invalid = 100,
   CXCallingConv_Unexposed = 200
 };
 
 /**
  * The type of an element in the abstract syntax tree.
  *

clang/include/clang/Basic/Attr.td

 }
 
 def SwiftCall : DeclOrTypeAttr {
   let Spellings = [Clang<"swiftcall">];
 //  let Subjects = SubjectList<[Function]>;
   let Documentation = [SwiftCallDocs];
 }
 
+def SwiftAsyncCall : DeclOrTypeAttr {
+  let Spellings = [Clang<"swiftasynccall">];
+  let Documentation = [SwiftAsyncCallDocs];
+}
+
 def SwiftContext : ParameterABIAttr {
   let Spellings = [Clang<"swift_context">];
   let Documentation = [SwiftContextDocs];
 }
 
 def SwiftAsyncContext : ParameterABIAttr {
   let Spellings = [Clang<"swift_async_context">];
   let Documentation = [SwiftAsyncContextDocs];

clang/include/clang/Basic/AttrDocs.td

 A ``swift_context`` parameter must either be the last parameter or must be
 followed by a ``swift_error_result`` parameter (which itself must always be
 the last parameter).
 
 A context parameter must have pointer or reference type.
   }];
 }
 
+def SwiftAsyncCallDocs : Documentation {
+  let Category = DocCatVariable;
+  let Content = [{
+The ``swiftasynccall`` attribute indicates that a function is
+compatible with the low-level conventions of Swift async functions,
+provided it declares the right formal arguments.
+
+In most respects, this is similar to the ``swiftcall`` attribute, except for
+the following:
+- A parameter may be marked ``swift_async_context``, but the parameter
+  attributes ``swift_context``, ``swift_error_result`` and
+  ``swift_indirect_result`` are not permitted.
+- A ``swiftasynccall`` function must have return type ``void``.
+- Within a ``swiftasynccall`` function, a call to a ``swiftasynccall``
+  function that is the immediate operand of a ``return`` statement is
+  guaranteed to be performed as a tail call. This syntax is allowed even
+  in C as an extension (a call to a void-returning function cannot be a
+  return operand in standard C). If something in the calling function would
+  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.
+  }];
+}
+
 def SwiftAsyncContextDocs : Documentation {
   let Category = DocCatVariable;
   let Content = [{
-The ``swift_async_context`` attribute marks a parameter as having the
-special asynchronous context-parameter ABI treatment.
+The ``swift_async_context`` attribute marks a parameter of a ``swiftasynccall``
+function as having the special asynchronous context-parameter ABI treatment.
 
 This treatment generally passes the context value in a special register
 which is normally callee-preserved.
 
 A context parameter must have pointer or reference type.
   }];
 }
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

def warn_objc_collection_literal_element : Warning<
   "%select{array element type|dictionary key type|dictionary value type}1 %2">,
   InGroup<ObjCLiteralConversion>;
 def warn_nsdictionary_duplicate_key : Warning<
   "duplicate key in dictionary literal">,
   InGroup<DiagGroup<"objc-dictionary-duplicate-keys">>;
 def note_nsdictionary_duplicate_key_here : Note<
   "previous equal key is here">;
 def err_swift_param_attr_not_swiftcall : Error<
-  "'%0' parameter can only be used with swiftcall calling convention">;
+  "'%0' parameter can only be used with %select{swiftcall|swiftasynccall}1 "
+  "calling convention">;
 def err_swift_indirect_result_not_first : Error<
   "'swift_indirect_result' parameters must be first parameters of function">;
 def err_swift_error_result_not_after_swift_context : Error<
   "'swift_error_result' parameter must follow 'swift_context' parameter">;
 def err_swift_abi_parameter_wrong_type : Error<
   "'%0' parameter must have pointer%select{| to unqualified pointer}1 type; "
   "type here is %2">;
 

clang/include/clang/Basic/Specifiers.h

#include "clang/Basic/OpenCLImageTypes.def"
   enum InClassInitStyle {
     ICIS_NoInit,   ///< No in-class initializer.
     ICIS_CopyInit, ///< Copy initialization.
     ICIS_ListInit  ///< Direct list-initialization.
   };
 
   /// CallingConv - Specifies the calling convention that a function uses.
   enum CallingConv {
-    CC_C,           // __attribute__((cdecl))
-    CC_X86StdCall,  // __attribute__((stdcall))
-    CC_X86FastCall, // __attribute__((fastcall))
-    CC_X86ThisCall, // __attribute__((thiscall))
-    CC_X86VectorCall, // __attribute__((vectorcall))
-    CC_X86Pascal,   // __attribute__((pascal))
-    CC_Win64,       // __attribute__((ms_abi))
-    CC_X86_64SysV,  // __attribute__((sysv_abi))
-    CC_X86RegCall, // __attribute__((regcall))
-    CC_AAPCS,       // __attribute__((pcs("aapcs")))
-    CC_AAPCS_VFP,   // __attribute__((pcs("aapcs-vfp")))
-    CC_IntelOclBicc, // __attribute__((intel_ocl_bicc))
-    CC_SpirFunction, // default for OpenCL functions on SPIR target
-    CC_OpenCLKernel, // inferred for OpenCL kernels
-    CC_Swift,        // __attribute__((swiftcall))
-    CC_PreserveMost, // __attribute__((preserve_most))
-    CC_PreserveAll,  // __attribute__((preserve_all))
+    CC_C,                 // __attribute__((cdecl))
+    CC_X86StdCall,        // __attribute__((stdcall))
+    CC_X86FastCall,       // __attribute__((fastcall))
+    CC_X86ThisCall,       // __attribute__((thiscall))
+    CC_X86VectorCall,     // __attribute__((vectorcall))
+    CC_X86Pascal,         // __attribute__((pascal))
+    CC_Win64,             // __attribute__((ms_abi))
+    CC_X86_64SysV,        // __attribute__((sysv_abi))
+    CC_X86RegCall,        // __attribute__((regcall))
+    CC_AAPCS,             // __attribute__((pcs("aapcs")))
+    CC_AAPCS_VFP,         // __attribute__((pcs("aapcs-vfp")))
+    CC_IntelOclBicc,      // __attribute__((intel_ocl_bicc))
+    CC_SpirFunction,      // default for OpenCL functions on SPIR target
+    CC_OpenCLKernel,      // inferred for OpenCL kernels
+    CC_Swift,             // __attribute__((swiftcall))
+    CC_SwiftAsync,        // __attribute__((swiftasynccall))
+    CC_PreserveMost,      // __attribute__((preserve_most))
+    CC_PreserveAll,       // __attribute__((preserve_all))
     CC_AArch64VectorCall, // __attribute__((aarch64_vector_pcs))
   };
 
   /// Checks whether the given calling convention supports variadic
   /// calls. Unprototyped calls also use the variadic call rules.
   inline bool supportsVariadicCall(CallingConv CC) {
     switch (CC) {
     case CC_X86StdCall:
     case CC_X86FastCall:
     case CC_X86ThisCall:
     case CC_X86RegCall:
     case CC_X86Pascal:
     case CC_X86VectorCall:
     case CC_SpirFunction:
     case CC_OpenCLKernel:
     case CC_Swift:
+    case CC_SwiftAsync:
       return false;
     default:
       return true;
     }
   }
 
   /// The storage duration for an object (per C++ [basic.stc]).
   enum StorageDuration {

clang/include/clang/CodeGen/SwiftCallingConv.h

 //==-- SwiftCallingConv.h - Swift ABI lowering ------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
-// Defines constants and types related to Swift ABI lowering.
+// Defines constants and types related to Swift ABI lowering. The same ABI
+// lowering applies to both sync and async functions.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_CODEGEN_SWIFTCALLINGCONV_H
 #define LLVM_CLANG_CODEGEN_SWIFTCALLINGCONV_H
 
 #include "clang/AST/CanonicalType.h"
 #include "clang/AST/CharUnits.h"

clang/lib/AST/ItaniumMangle.cpp

StringRef CXXNameMangler::getCallingConvQualifierName(CallingConv CC) {
   case CC_X86FastCall:
     return "fastcall";
   case CC_X86_64SysV:
     return "sysv_abi";
   case CC_Win64:
     return "ms_abi";
   case CC_Swift:
     return "swiftcall";
+  case CC_SwiftAsync:
+    return "swiftasynccall";
   }
   llvm_unreachable("bad calling convention");
 }
 
 void CXXNameMangler::mangleExtFunctionInfo(const FunctionType *T) {
   // Fast path.
   if (T->getExtInfo() == FunctionType::ExtInfo())
     return;

clang/lib/AST/MicrosoftMangle.cpp

void MicrosoftCXXNameMangler::mangleCallingConvention(CallingConv CC) {
   //                      ::= E # __thiscall
   //                      ::= F # __export __thiscall
   //                      ::= G # __stdcall
   //                      ::= H # __export __stdcall
   //                      ::= I # __fastcall
   //                      ::= J # __export __fastcall
   //                      ::= Q # __vectorcall
   //                      ::= S # __attribute__((__swiftcall__)) // Clang-only
+  //                      ::= T # __attribute__((__swiftasynccall__))
+  //                            // Clang-only
   //                      ::= w # __regcall
   // The 'export' calling conventions are from a bygone era
   // (*cough*Win16*cough*) when functions were declared for export with
   // that keyword. (It didn't actually export them, it just made them so
   // that they could be in a DLL and somebody from another module could call
   // them.)
 
   switch (CC) {
     default:
       llvm_unreachable("Unsupported CC for mangling");
     case CC_Win64:
     case CC_X86_64SysV:
     case CC_C: Out << 'A'; break;
     case CC_X86Pascal: Out << 'C'; break;
     case CC_X86ThisCall: Out << 'E'; break;
     case CC_X86StdCall: Out << 'G'; break;
     case CC_X86FastCall: Out << 'I'; break;
     case CC_X86VectorCall: Out << 'Q'; break;
     case CC_Swift: Out << 'S'; break;
+    case CC_SwiftAsync: Out << 'T'; break;
     case CC_PreserveMost: Out << 'U'; break;
     case CC_X86RegCall: Out << 'w'; break;
   }
 }
 void MicrosoftCXXNameMangler::mangleCallingConvention(const FunctionType *T) {
   mangleCallingConvention(T->getCallConv());
 }
 
 void MicrosoftCXXNameMangler::mangleThrowSpecification(
                                                 const FunctionProtoType *FT) {

clang/lib/AST/Type.cpp

StringRef FunctionType::getNameForCallConv(CallingConv CC) {
   case CC_X86RegCall : return "regcall";
   case CC_AAPCS: return "aapcs";
   case CC_AAPCS_VFP: return "aapcs-vfp";
   case CC_AArch64VectorCall: return "aarch64_vector_pcs";
   case CC_IntelOclBicc: return "intel_ocl_bicc";
   case CC_SpirFunction: return "spir_function";
   case CC_OpenCLKernel: return "opencl_kernel";
   case CC_Swift: return "swiftcall";
+  case CC_SwiftAsync: return "swiftasynccall";
   case CC_PreserveMost: return "preserve_most";
   case CC_PreserveAll: return "preserve_all";
   }
 
   llvm_unreachable("Invalid calling convention.");
 }
 
 FunctionProtoType::FunctionProtoType(QualType result, ArrayRef<QualType> params,
bool AttributedType::isCallingConv() const {
   default: return false;
   case attr::Pcs:
   case attr::CDecl:
   case attr::FastCall:
   case attr::StdCall:
   case attr::ThisCall:
   case attr::RegCall:
   case attr::SwiftCall:
+  case attr::SwiftAsyncCall:
   case attr::VectorCall:
   case attr::AArch64VectorPcs:
   case attr::Pascal:
   case attr::MSABI:
   case attr::SysVABI:
   case attr::IntelOclBicc:
   case attr::PreserveMost:
   case attr::PreserveAll:

clang/lib/AST/TypePrinter.cpp

case CC_X86RegCall:
       break;
     case CC_SpirFunction:
     case CC_OpenCLKernel:
       // Do nothing. These CCs are not available as attributes.
       break;
     case CC_Swift:
       OS << " __attribute__((swiftcall))";
       break;
+    case CC_SwiftAsync:
+      OS << "__attribute__((swiftasynccall))";
+      break;
     case CC_PreserveMost:
       OS << " __attribute__((preserve_most))";
       break;
     case CC_PreserveAll:
       OS << " __attribute__((preserve_all))";
       break;
     }
   }
#include "clang/Basic/AttrList.inc"
   // FIXME: When Sema learns to form this AttributedType, avoid printing the
   // attribute again in printFunctionProtoAfter.
   case attr::AnyX86NoCfCheck: OS << "nocf_check"; break;
   case attr::CDecl: OS << "cdecl"; break;
   case attr::FastCall: OS << "fastcall"; break;
   case attr::StdCall: OS << "stdcall"; break;
   case attr::ThisCall: OS << "thiscall"; break;
   case attr::SwiftCall: OS << "swiftcall"; break;
+  case attr::SwiftAsyncCall: OS << "swiftasynccall"; break;
   case attr::VectorCall: OS << "vectorcall"; break;
   case attr::Pascal: OS << "pascal"; break;
   case attr::MSABI: OS << "ms_abi"; break;
   case attr::SysVABI: OS << "sysv_abi"; break;
   case attr::RegCall: OS << "regcall"; break;
   case attr::Pcs: {
     OS << "pcs(";
    QualType t = T->getEquivalentType();

clang/lib/Basic/Targets/AArch64.cpp

bool AArch64TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
   return true;
 }
 
 TargetInfo::CallingConvCheckResult
 AArch64TargetInfo::checkCallingConvention(CallingConv CC) const {
   switch (CC) {
   case CC_C:
   case CC_Swift:
+  case CC_SwiftAsync:
   case CC_PreserveMost:
   case CC_PreserveAll:
   case CC_OpenCLKernel:
   case CC_AArch64VectorCall:
   case CC_Win64:
     return CCCR_OK;
   default:
     return CCCR_Warning;
WindowsARM64TargetInfo::checkCallingConvention(CallingConv CC) const {
   case CC_X86FastCall:
   case CC_X86VectorCall:
     return CCCR_Ignore;
   case CC_C:
   case CC_OpenCLKernel:
   case CC_PreserveMost:
   case CC_PreserveAll:
   case CC_Swift:
+  case CC_SwiftAsync:
   case CC_Win64:
     return CCCR_OK;
   default:
     return CCCR_Warning;
   }
 }
 
 MicrosoftARM64TargetInfo::MicrosoftARM64TargetInfo(const llvm::Triple &Triple,

clang/lib/Basic/Targets/ARM.cpp

 }
 
 TargetInfo::CallingConvCheckResult
 ARMTargetInfo::checkCallingConvention(CallingConv CC) const {
   switch (CC) {
   case CC_AAPCS:
   case CC_AAPCS_VFP:
   case CC_Swift:
+  case CC_SwiftAsync:
   case CC_OpenCLKernel:
     return CCCR_OK;
   default:
     return CCCR_Warning;
   }
 }
 
 int ARMTargetInfo::getEHDataRegisterNumber(unsigned RegNo) const {
WindowsARMTargetInfo::checkCallingConvention(CallingConv CC) const {
   case CC_X86FastCall:
   case CC_X86VectorCall:
     return CCCR_Ignore;
   case CC_C:
   case CC_OpenCLKernel:
   case CC_PreserveMost:
   case CC_PreserveAll:
   case CC_Swift:
+  case CC_SwiftAsync:
     return CCCR_OK;
   default:
     return CCCR_Warning;
   }
 }
 
 // Windows ARM + Itanium C++ ABI Target
 ItaniumWindowsARMleTargetInfo::ItaniumWindowsARMleTargetInfo(

clang/lib/Basic/Targets/PPC.h

if (Name == "elfv1" || Name == "elfv2") {
       return true;
     }
     return false;
   }
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     switch (CC) {
     case CC_Swift:
+    case CC_SwiftAsync:
       return CCCR_OK;
     default:
       return CCCR_Warning;
     }
   }
 };
 
 class LLVM_LIBRARY_VISIBILITY DarwinPPC32TargetInfo

clang/lib/Basic/Targets/SystemZ.h

public:
   }
 
   bool hasFeature(StringRef Feature) const override;
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     switch (CC) {
     case CC_C:
     case CC_Swift:
+    case CC_SwiftAsync:
     case CC_OpenCLKernel:
       return CCCR_OK;
     default:
       return CCCR_Warning;
     }
   }
 
   StringRef getABI() const override {

clang/lib/Basic/Targets/WebAssembly.h

return BitWidth == 64
                ? (IsSigned ? SignedLongLong : UnsignedLongLong)
                : TargetInfo::getLeastIntTypeByWidth(BitWidth, IsSigned);
   }
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     switch (CC) {
     case CC_C:
     case CC_Swift:
+    case CC_SwiftAsync:
       return CCCR_OK;
     default:
       return CCCR_Warning;
     }
   }
 
   bool hasExtIntType() const override { return true; }
 

clang/lib/Basic/Targets/X86.h

CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     case CC_X86ThisCall:
     case CC_X86FastCall:
     case CC_X86StdCall:
     case CC_X86VectorCall:
     case CC_X86RegCall:
     case CC_C:
     case CC_PreserveMost:
     case CC_Swift:
+    case CC_SwiftAsync:
     case CC_X86Pascal:
     case CC_IntelOclBicc:
     case CC_OpenCLKernel:
       return CCCR_OK;
     default:
       return CCCR_Warning;
     }
   }
if (RegNo == 1)
       return 1;
     return -1;
   }
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     switch (CC) {
     case CC_C:
     case CC_Swift:
+    case CC_SwiftAsync:
     case CC_X86VectorCall:
     case CC_IntelOclBicc:
     case CC_Win64:
     case CC_PreserveMost:
     case CC_PreserveAll:
     case CC_X86RegCall:
     case CC_OpenCLKernel:
       return CCCR_OK;
case CC_X86FastCall:
       return CCCR_Ignore;
     case CC_C:
     case CC_X86VectorCall:
     case CC_IntelOclBicc:
     case CC_PreserveMost:
     case CC_PreserveAll:
     case CC_X86_64SysV:
     case CC_Swift:
+    case CC_SwiftAsync:
     case CC_X86RegCall:
     case CC_OpenCLKernel:
       return CCCR_OK;
     default:
       return CCCR_Warning;
     }
   }
 };

clang/lib/CodeGen/CGCall.cpp

unsigned CodeGenTypes::ClangCallConvToLLVMCallConv(CallingConv CC) {
   // TODO: Add support for __vectorcall to LLVM.
   case CC_X86VectorCall: return llvm::CallingConv::X86_VectorCall;
   case CC_AArch64VectorCall: return llvm::CallingConv::AArch64_VectorCall;
   case CC_SpirFunction: return llvm::CallingConv::SPIR_FUNC;
   case CC_OpenCLKernel: return CGM.getTargetCodeGenInfo().getOpenCLKernelCallingConv();
   case CC_PreserveMost: return llvm::CallingConv::PreserveMost;
   case CC_PreserveAll: return llvm::CallingConv::PreserveAll;
   case CC_Swift: return llvm::CallingConv::Swift;
+  // [FIXME: swiftasynccc] Update to SwiftAsync once LLVM support lands.
+  case CC_SwiftAsync:
+    return llvm::CallingConv::Swift;
   }
 }
 
 /// Derives the 'this' type for codegen purposes, i.e. ignoring method CVR
 /// qualification. Either or both of RD and MD may be null. A null RD indicates
 /// that there is no meaningful 'this' type, and a null MD can occur when
 /// calling a method pointer.
 CanQualType CodeGenTypes::DeriveThisType(const CXXRecordDecl *RD,
CodeGenTypes::arrangeLLVMFunctionInfo(CanQualType resultType,
   (void)inserted;
   assert(inserted && "Recursively being processed?");
 
   // Compute ABI information.
   if (CC == llvm::CallingConv::SPIR_KERNEL) {
     // Force target independent argument handling for the host visible
     // kernel functions.
     computeSPIRKernelABIInfo(CGM, *FI);
-  } else if (info.getCC() == CC_Swift) {
+  } else if (info.getCC() == CC_Swift || info.getCC() == CC_SwiftAsync) {
     swiftcall::computeABIInfo(CGM, *FI);
   } else {
     getABIInfo().computeInfo(*FI);
   }
 
   // Loop over all of the computed argument and return value info.  If any of
   // them are direct or extend without a specified coerce type, specify the
   // default now.
void CodeGenFunction::EmitNonNullArgCheck(RValue RV, QualType ArgType,
   EmitCheck(std::make_pair(Cond, CheckKind), Handler, StaticData, None);
 }
 
 // Check if the call is going to use the inalloca convention. This needs to
 // agree with CGFunctionInfo::usesInAlloca. The CGFunctionInfo is arranged
 // later, so we can't check it directly.
 static bool hasInAllocaArgs(CodeGenModule &CGM, CallingConv ExplicitCC,
                             ArrayRef<QualType> ArgTypes) {
-  // The Swift calling convention doesn't go through the target-specific
-  // argument classification, so it never uses inalloca.
+  // The Swift calling conventions don't go through the target-specific
+  // argument classification, they never use inalloca.
   // TODO: Consider limiting inalloca use to only calling conventions supported
   // by MSVC.
-  if (ExplicitCC == CC_Swift)
+  if (ExplicitCC == CC_Swift || ExplicitCC == CC_SwiftAsync)
     return false;
   if (!CGM.getTarget().getCXXABI().isMicrosoft())
     return false;
   return llvm::any_of(ArgTypes, [&](QualType Ty) {
     return isInAllocaArgument(CGM.getCXXABI(), Ty);
   });
 }
 

clang/lib/CodeGen/CGDebugInfo.cpp

static unsigned getDwarfCC(CallingConv CC) {
   case CC_IntelOclBicc:
     return llvm::dwarf::DW_CC_LLVM_IntelOclBicc;
   case CC_SpirFunction:
     return llvm::dwarf::DW_CC_LLVM_SpirFunction;
   case CC_OpenCLKernel:
     return llvm::dwarf::DW_CC_LLVM_OpenCLKernel;
   case CC_Swift:
     return llvm::dwarf::DW_CC_LLVM_Swift;
+  case CC_SwiftAsync:
+    // [FIXME: swiftasynccc] Update to SwiftAsync once LLVM support lands.
+    return llvm::dwarf::DW_CC_LLVM_Swift;
   case CC_PreserveMost:
     return llvm::dwarf::DW_CC_LLVM_PreserveMost;
   case CC_PreserveAll:
     return llvm::dwarf::DW_CC_LLVM_PreserveAll;
   case CC_X86RegCall:
     return llvm::dwarf::DW_CC_LLVM_X86RegCall;
   }
   return 0;

clang/lib/Sema/SemaDeclAttr.cpp

case ParsedAttr::AT_CDecl:
     D->addAttr(::new (S.Context) CDeclAttr(S.Context, AL));
     return;
   case ParsedAttr::AT_Pascal:
     D->addAttr(::new (S.Context) PascalAttr(S.Context, AL));
     return;
   case ParsedAttr::AT_SwiftCall:
     D->addAttr(::new (S.Context) SwiftCallAttr(S.Context, AL));
     return;
+  case ParsedAttr::AT_SwiftAsyncCall:
+    D->addAttr(::new (S.Context) SwiftAsyncCallAttr(S.Context, AL));
+    return;
   case ParsedAttr::AT_VectorCall:
     D->addAttr(::new (S.Context) VectorCallAttr(S.Context, AL));
     return;
   case ParsedAttr::AT_MSABI:
     D->addAttr(::new (S.Context) MSABIAttr(S.Context, AL));
     return;
   case ParsedAttr::AT_SysVABI:
     D->addAttr(::new (S.Context) SysVABIAttr(S.Context, AL));
case ParsedAttr::AT_ThisCall:
     CC = CC_X86ThisCall;
     break;
   case ParsedAttr::AT_Pascal:
     CC = CC_X86Pascal;
     break;
   case ParsedAttr::AT_SwiftCall:
     CC = CC_Swift;
     break;
+  case ParsedAttr::AT_SwiftAsyncCall:
+    CC = CC_SwiftAsync;
+    break;
   case ParsedAttr::AT_VectorCall:
     CC = CC_X86VectorCall;
     break;
   case ParsedAttr::AT_AArch64VectorPcs:
     CC = CC_AArch64VectorCall;
     break;
   case ParsedAttr::AT_RegCall:
     CC = CC_X86RegCall;
case ParsedAttr::AT_CmseNSEntry:
     break;
   case ParsedAttr::AT_StdCall:
   case ParsedAttr::AT_CDecl:
   case ParsedAttr::AT_FastCall:
   case ParsedAttr::AT_ThisCall:
   case ParsedAttr::AT_Pascal:
   case ParsedAttr::AT_RegCall:
   case ParsedAttr::AT_SwiftCall:
+  case ParsedAttr::AT_SwiftAsyncCall:
   case ParsedAttr::AT_VectorCall:
   case ParsedAttr::AT_MSABI:
   case ParsedAttr::AT_SysVABI:
   case ParsedAttr::AT_Pcs:
   case ParsedAttr::AT_IntelOclBicc:
   case ParsedAttr::AT_PreserveMost:
   case ParsedAttr::AT_PreserveAll:
   case ParsedAttr::AT_AArch64VectorPcs:
     handleCallConvAttr(S, D, AL);
     break;
   case ParsedAttr::AT_Suppress:
     handleSuppressAttr(S, D, AL);
     break;
   case ParsedAttr::AT_Owner:
   case ParsedAttr::AT_Pointer:
     handleLifetimeCategoryAttr(S, D, AL);
     break;

clang/lib/Sema/SemaType.cpp

 #define CALLING_CONV_ATTRS_CASELIST                                            \
   case ParsedAttr::AT_CDecl:                                                   \
   case ParsedAttr::AT_FastCall:                                                \
   case ParsedAttr::AT_StdCall:                                                 \
   case ParsedAttr::AT_ThisCall:                                                \
   case ParsedAttr::AT_RegCall:                                                 \
   case ParsedAttr::AT_Pascal:                                                  \
   case ParsedAttr::AT_SwiftCall:                                               \
+  case ParsedAttr::AT_SwiftAsyncCall:                                          \
   case ParsedAttr::AT_VectorCall:                                              \
   case ParsedAttr::AT_AArch64VectorPcs:                                        \
   case ParsedAttr::AT_MSABI:                                                   \
   case ParsedAttr::AT_SysVABI:                                                 \
   case ParsedAttr::AT_Pcs:                                                     \
   case ParsedAttr::AT_IntelOclBicc:                                            \
   case ParsedAttr::AT_PreserveMost:                                            \
   case ParsedAttr::AT_PreserveAll

 /// checking should occur when applying the parameter attribute; the
 /// only other checks required are positional restrictions.
 static void checkExtParameterInfos(Sema &S, ArrayRef<QualType> paramTypes,
                     const FunctionProtoType::ExtProtoInfo &EPI,
                     llvm::function_ref<SourceLocation(unsigned)> getParamLoc) {
   assert(EPI.ExtParameterInfos && "shouldn't get here without param infos");
 
   bool hasCheckedSwiftCall = false;
+  bool hasCheckedSwiftAsyncCall = false;
+  auto reportWrongABI = [&](unsigned paramIndex, bool shouldBeAsync) {
+    S.Diag(getParamLoc(paramIndex), diag::err_swift_param_attr_not_swiftcall)
+        << getParameterABISpelling(EPI.ExtParameterInfos[paramIndex].getABI())
+        << shouldBeAsync;
+  };
   auto checkForSwiftCC = [&](unsigned paramIndex) {
     // Only do this once.
     if (hasCheckedSwiftCall) return;
     hasCheckedSwiftCall = true;
     if (EPI.ExtInfo.getCC() == CC_Swift) return;
-    S.Diag(getParamLoc(paramIndex), diag::err_swift_param_attr_not_swiftcall)
-      << getParameterABISpelling(EPI.ExtParameterInfos[paramIndex].getABI());
+    reportWrongABI(paramIndex, false);
   };
 
   for (size_t paramIndex = 0, numParams = paramTypes.size();
           paramIndex != numParams; ++paramIndex) {
     switch (EPI.ExtParameterInfos[paramIndex].getABI()) {
     // Nothing interesting to check for orindary-ABI parameters.
     case ParameterABI::Ordinary:
       continue;
case ParameterABI::SwiftIndirectResult:
       }
       continue;
 
     case ParameterABI::SwiftContext:
       checkForSwiftCC(paramIndex);
       continue;
 
     case ParameterABI::SwiftAsyncContext:
-      // FIXME: might want to require swiftasynccc when it exists
+      if (!hasCheckedSwiftAsyncCall && EPI.ExtInfo.getCC() != CC_SwiftAsync) {
+        reportWrongABI(paramIndex, true);
+      }
+      hasCheckedSwiftAsyncCall = true;
       continue;
 
     // swift_error parameters must be preceded by a swift_context parameter.
     case ParameterABI::SwiftErrorResult:
       checkForSwiftCC(paramIndex);
       if (paramIndex == 0 ||
           EPI.ExtParameterInfos[paramIndex - 1].getABI() !=
               ParameterABI::SwiftContext) {
static Attr *getCCTypeAttr(ASTContext &Ctx, ParsedAttr &Attr) {
   case ParsedAttr::AT_ThisCall:
     return createSimpleAttr<ThisCallAttr>(Ctx, Attr);
   case ParsedAttr::AT_RegCall:
     return createSimpleAttr<RegCallAttr>(Ctx, Attr);
   case ParsedAttr::AT_Pascal:
     return createSimpleAttr<PascalAttr>(Ctx, Attr);
   case ParsedAttr::AT_SwiftCall:
     return createSimpleAttr<SwiftCallAttr>(Ctx, Attr);
+  case ParsedAttr::AT_SwiftAsyncCall:
+    return createSimpleAttr<SwiftAsyncCallAttr>(Ctx, Attr);
   case ParsedAttr::AT_VectorCall:
     return createSimpleAttr<VectorCallAttr>(Ctx, Attr);
   case ParsedAttr::AT_AArch64VectorPcs:
     return createSimpleAttr<AArch64VectorPcsAttr>(Ctx, Attr);
   case ParsedAttr::AT_Pcs: {
     // The attribute may have had a fixit applied where we treated an
     // identifier as a string literal.  The contents of the string are valid,
     // but the form may not be.

clang/test/CodeGen/arm-swiftcall.c

 // RUN: %clang_cc1 -triple armv7-apple-darwin9 -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple armv7s-apple-ios9 -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple armv7k-apple-ios9 -emit-llvm -o - %s | FileCheck %s
 
 #define SWIFTCALL __attribute__((swiftcall))
+#define SWIFTASYNCCALL __attribute__((swiftasynccall))
 #define OUT __attribute__((swift_indirect_result))
 #define ERROR __attribute__((swift_error_result))
 #define CONTEXT __attribute__((swift_context))
 #define ASYNC_CONTEXT __attribute__((swift_async_context))
 
 /*****************************************************************************/
 /****************************** PARAMETER ABIS *******************************/
 /*****************************************************************************/

 // CHECK:       store float* [[T0]], float** [[TEMP]], align 4
 // CHECK:       call [[SWIFTCC:swiftcc]] void @context_error_1(i32* swiftself [[X]], float** swifterror [[TEMP]])
 // CHECK:       [[T0:%.*]] = load float*, float** [[TEMP]], align 4
 // CHECK:       store float* [[T0]], float** [[ERROR]], align 4
 
 SWIFTCALL void context_error_2(short s, CONTEXT int *self, ERROR float **error) {}
 // CHECK-LABEL: define{{.*}} void @context_error_2(i16{{.*}}, i32* swiftself{{.*}}, float** swifterror %0)
 
-SWIFTCALL void async_context_1(ASYNC_CONTEXT void *self) {}
+SWIFTASYNCCALL void async_context_1(ASYNC_CONTEXT void *self) {}
 // CHECK-LABEL: define {{.*}} void @async_context_1(i8* swiftasync
 
 /*****************************************************************************/
 /********************************** LOWERING *********************************/
 /*****************************************************************************/
 
 typedef float float3 __attribute__((ext_vector_type(3)));
 typedef float float4 __attribute__((ext_vector_type(4)));

clang/test/CodeGen/debug-info-cc.c

 //    CC_X86_64SysV,  // __attribute__((sysv_abi))
 //    CC_X86RegCall, // __attribute__((regcall))
 //    CC_AAPCS,       // __attribute__((pcs("aapcs")))
 //    CC_AAPCS_VFP,   // __attribute__((pcs("aapcs-vfp")))
 //    CC_IntelOclBicc, // __attribute__((intel_ocl_bicc))
 //    CC_SpirFunction, // default for OpenCL functions on SPIR target
 //    CC_OpenCLKernel, // inferred for OpenCL kernels
 //    CC_Swift,        // __attribute__((swiftcall))
+//    CC_SwiftAsync,   // __attribute__((swiftasynccall))
 //    CC_PreserveMost, // __attribute__((preserve_most))
 //    CC_PreserveAll,  // __attribute__((preserve_all))
 //  };
 
 #ifdef __x86_64__
 
 #ifdef __linux__
 // LINUX: !DISubprogram({{.*}}"add_msabi", {{.*}}type: ![[FTY:[0-9]+]]

 }
 
 // LINUX: !DISubprogram({{.*}}"add_swiftcall", {{.*}}type: ![[FTY:[0-9]+]]
 // LINUX: ![[FTY]] = !DISubroutineType({{.*}}cc: DW_CC_LLVM_Swift,
 __attribute__((swiftcall)) int add_swiftcall(int a, int b) {
   return a+b;
 }
 
+// [FIXME: swiftasynccc] Update debuginfo tag to SwiftAsync once LLVM support lands.
+// LINUX: !DISubprogram({{.*}}"add_swiftasynccall", {{.*}}type: ![[FTY:[0-9]+]]
+// LINUX: ![[FTY]] = !DISubroutineType({{.*}}cc: DW_CC_LLVM_Swift,
+__attribute__((swiftasynccall)) int add_swiftasynccall(int a, int b) {
+  return a+b;
+}
+
 // LINUX: !DISubprogram({{.*}}"add_inteloclbicc", {{.*}}type: ![[FTY:[0-9]+]]
 // LINUX: ![[FTY]] = !DISubroutineType({{.*}}cc: DW_CC_LLVM_IntelOclBicc,
 __attribute__((intel_ocl_bicc)) int add_inteloclbicc(int a, int b) {
   return a+b;
 }
 #endif
 
 #ifdef _WIN64

clang/test/Sema/attr-c2x.c

enum [[clang::flag_enum]] EnumFlag {
   D0 = 1, D1 = 8
 };
 
 void foo(void *c) [[clang::overloadable]];
 void foo(char *c) [[clang::overloadable]];
 
 void context_okay(void *context [[clang::swift_context]]) [[clang::swiftcall]];
 void context_okay2(void *context [[clang::swift_context]], void *selfType, char **selfWitnessTable) [[clang::swiftcall]];
+void context_async_okay(void *context [[clang::swift_async_context]]) [[clang::swiftasynccall]];
+void context_async_okay2(void *context [[clang::swift_async_context]], void *selfType, char **selfWitnessTable) [[clang::swiftasynccall]];
 
 void *f1(void) [[clang::ownership_returns(foo)]];
 void *f2() [[clang::ownership_returns(foo)]]; // expected-warning {{'ownership_returns' attribute only applies to non-K&R-style functions}}
 
 void foo2(void) [[clang::unavailable("not available - replaced")]]; // expected-note {{'foo2' has been explicitly marked unavailable here}}
 void bar(void) {
   foo2(); // expected-error {{'foo2' is unavailable: not available - replaced}}
 }

clang/test/Sema/attr-swiftcall.c

 // RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -verify %s
 // RUN: %clang_cc1 -triple x86_64-unknown-windows -fsyntax-only -verify %s
 
 #define SWIFTCALL __attribute__((swiftcall))
+#define SWIFTASYNCCALL __attribute__((swiftasynccall))
 #define INDIRECT_RESULT __attribute__((swift_indirect_result))
 #define ERROR_RESULT __attribute__((swift_error_result))
 #define CONTEXT __attribute__((swift_context))
 #define ASYNC_CONTEXT __attribute__((swift_async_context))
 
 int notAFunction SWIFTCALL; // expected-warning {{'swiftcall' only applies to function types; type here is 'int'}}
+int notAnAsyncFunction SWIFTASYNCCALL; // expected-warning {{'swiftasynccall' only applies to function types; type here is 'int'}}
 void variadic(int x, ...) SWIFTCALL; // expected-error {{variadic function cannot use swiftcall calling convention}}
+void variadic_async(int x, ...) SWIFTASYNCCALL; // expected-error {{variadic function cannot use swiftasynccall calling convention}}
 void unprototyped() SWIFTCALL; // expected-error {{function with no prototype cannot use the swiftcall calling convention}}
+void unprototyped_async() SWIFTASYNCCALL; // expected-error {{function with no prototype cannot use the swiftasynccall calling convention}}
 void multiple_ccs(int x) SWIFTCALL __attribute__((vectorcall)); // expected-error {{vectorcall and swiftcall attributes are not compatible}}
+void multiple_ccs_async(int x) SWIFTASYNCCALL __attribute__((vectorcall)); // expected-error {{vectorcall and swiftasynccall attributes are not compatible}}
 void (*functionPointer)(void) SWIFTCALL;
+void (*asyncFunctionPointer)(void) SWIFTASYNCCALL;
 
 void indirect_result_nonswift(INDIRECT_RESULT void *out); // expected-error {{'swift_indirect_result' parameter can only be used with swiftcall calling convention}}
 void indirect_result_bad_position(int first, INDIRECT_RESULT void *out) SWIFTCALL; // expected-error {{'swift_indirect_result' parameters must be first parameters of function}}
 void indirect_result_bad_type(INDIRECT_RESULT int out) SWIFTCALL; // expected-error {{'swift_indirect_result' parameter must have pointer type; type here is 'int'}}
 void indirect_result_single(INDIRECT_RESULT void *out) SWIFTCALL;
 void indirect_result_multiple(INDIRECT_RESULT void *out1, INDIRECT_RESULT void *out2) SWIFTCALL;
 
 void error_result_nonswift(ERROR_RESULT void **error); // expected-error {{'swift_error_result' parameter can only be used with swiftcall calling convention}} expected-error{{'swift_error_result' parameter must follow 'swift_context' parameter}}
 void error_result_bad_position2(int first, ERROR_RESULT void **error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must follow 'swift_context' parameter}}
 void error_result_bad_type(CONTEXT void *context, ERROR_RESULT int error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must have pointer to unqualified pointer type; type here is 'int'}}
 void error_result_bad_type2(CONTEXT void *context, ERROR_RESULT int *error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must have pointer to unqualified pointer type; type here is 'int *'}}
 void error_result_okay(int a, int b, CONTEXT void *context, ERROR_RESULT void **error) SWIFTCALL;
 void error_result_okay2(CONTEXT void *context, ERROR_RESULT void **error, void *selfType, char **selfWitnessTable) SWIFTCALL;
 
 void context_nonswift(CONTEXT void *context); // expected-error {{'swift_context' parameter can only be used with swiftcall calling convention}}
 void context_bad_type(CONTEXT int context) SWIFTCALL; // expected-error {{'swift_context' parameter must have pointer type; type here is 'int'}}
 void context_okay(CONTEXT void *context) SWIFTCALL;
 void context_okay2(CONTEXT void *context, void *selfType, char **selfWitnessTable) SWIFTCALL;
 
-void async_context_okay_for_now(ASYNC_CONTEXT void *context);
-void async_context_bad_type(ASYNC_CONTEXT int context) SWIFTCALL; // expected-error {{'swift_async_context' parameter must have pointer type; type here is 'int'}}
-void async_context_okay(ASYNC_CONTEXT void *context) SWIFTCALL;
-void async_context_okay2(ASYNC_CONTEXT void *context, void *selfType, char **selfWitnessTable) SWIFTCALL;
+void async_context_nonswift(ASYNC_CONTEXT void *context); // expected-error {{'swift_async_context' parameter can only be used with swiftasynccall calling convention}}
+void async_context_bad_type(ASYNC_CONTEXT int context) SWIFTASYNCCALL; // expected-error {{'swift_async_context' parameter must have pointer type; type here is 'int'}}
+void async_context_okay(ASYNC_CONTEXT void *context) SWIFTASYNCCALL;
+void async_context_okay2(void *someArg, ASYNC_CONTEXT void *context, void *otherArg) SWIFTASYNCCALL;

clang/test/Sema/no_callconv.cpp

 // RUN: %clang_cc1 %s -triple x86_64-scei-ps4 -DPS4 -fsyntax-only -verify
 // RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -fsyntax-only -verify
 
 #ifdef PS4
 
 // PS4 does not support these.
 void __vectorcall func_vc() {} // expected-error {{'__vectorcall' calling convention is not supported for this target}}
 void __regcall func_rc() {} // expected-error {{'__regcall' calling convention is not supported for this target}}
 void __attribute__((vectorcall)) funcA() {} // expected-error {{'vectorcall' calling convention is not supported for this target}}
 void __attribute__((regcall)) funcB() {} // expected-error {{'regcall' calling convention is not supported for this target}}
 void __attribute__((ms_abi)) funcH() {} // expected-error {{'ms_abi' calling convention is not supported for this target}}
 void __attribute__((intel_ocl_bicc)) funcJ() {} // expected-error {{'intel_ocl_bicc' calling convention is not supported for this target}}
 void __attribute__((swiftcall)) funcK() {} // expected-error {{'swiftcall' calling convention is not supported for this target}}
+void __attribute__((swiftasynccall)) funcKK() {} // expected-error {{'swiftasynccall' calling convention is not supported for this target}}
 void __attribute__((pascal)) funcG() {} // expected-error {{'pascal' calling convention is not supported for this target}}
 void __attribute__((preserve_most)) funcL() {} // expected-error {{'preserve_most' calling convention is not supported for this target}}
 void __attribute__((preserve_all)) funcM() {} // expected-error {{'preserve_all' calling convention is not supported for this target}}
 void __attribute__((stdcall)) funcD() {} // expected-error {{'stdcall' calling convention is not supported for this target}}
 void __attribute__((fastcall)) funcE() {} // expected-error {{'fastcall' calling convention is not supported for this target}}
 void __attribute__((thiscall)) funcF() {} // expected-error {{'thiscall' calling convention is not supported for this target}}
 #else
 
 void __vectorcall func_vc() {}
 void __regcall func_rc() {}
 void __attribute__((vectorcall)) funcA() {}
 void __attribute__((regcall)) funcB() {}
 void __attribute__((ms_abi)) funcH() {}
 void __attribute__((intel_ocl_bicc)) funcJ() {}
 void __attribute__((swiftcall)) funcK() {}
+void __attribute__((swiftasynccall)) funcKK() {}
 void __attribute__((preserve_most)) funcL() {}
 void __attribute__((preserve_all)) funcM() {}
 
 // Same function with different calling conventions. Error with a note pointing to the last decl.
 void __attribute__((preserve_all)) funcR(); // expected-note {{previous declaration is here}}
 void __attribute__((preserve_most)) funcR(); // expected-error {{function declared 'preserve_most' here was previously declared 'preserve_all'}}
 
 void __attribute__((pascal)) funcG() {} // expected-warning {{'pascal' calling convention is not supported for this target}}
 
 void __attribute__((stdcall)) funcD() {} // expected-warning {{'stdcall' calling convention is not supported for this target}}
 void __attribute__((fastcall)) funcE() {} // expected-warning {{'fastcall' calling convention is not supported for this target}}
 void __attribute__((thiscall)) funcF() {} // expected-warning {{'thiscall' calling convention is not supported for this target}}
 #endif
 
 void __attribute__((sysv_abi)) funcI() {}
 void __attribute__((cdecl)) funcC() {}

clang/test/SemaCXX/attr-swiftcall.cpp

 // RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -verify %s
 
 #define SWIFTCALL __attribute__((swiftcall))
+#define SWIFTASYNCCALL __attribute__((swiftasynccall))
 #define INDIRECT_RESULT __attribute__((swift_indirect_result))
 #define ERROR_RESULT __attribute__((swift_error_result))
 #define CONTEXT __attribute__((swift_context))
+#define ASYNC_CONTEXT __attribute__((swift_async_context))
 
 int notAFunction SWIFTCALL; // expected-warning {{'swiftcall' only applies to function types; type here is 'int'}}
+int notAnAsyncFunction SWIFTASYNCCALL; // expected-warning {{'swiftasynccall' only applies to function types; type here is 'int'}}
 void variadic(int x, ...) SWIFTCALL; // expected-error {{variadic function cannot use swiftcall calling convention}}
+void variadic_async(int x, ...) SWIFTASYNCCALL; // expected-error {{variadic function cannot use swiftasynccall calling convention}}
 void multiple_ccs(int x) SWIFTCALL __attribute__((vectorcall)); // expected-error {{vectorcall and swiftcall attributes are not compatible}}
+void multiple_ccs_async(int x) SWIFTASYNCCALL __attribute__((vectorcall)); // expected-error {{vectorcall and swiftasynccall attributes are not compatible}}
 void (*functionPointer)(void) SWIFTCALL;
+void (*asyncFunctionPointer)(void) SWIFTASYNCCALL;
 
 void indirect_result_nonswift(INDIRECT_RESULT void *out); // expected-error {{'swift_indirect_result' parameter can only be used with swiftcall calling convention}}
 void indirect_result_bad_position(int first, INDIRECT_RESULT void *out) SWIFTCALL; // expected-error {{'swift_indirect_result' parameters must be first parameters of function}}
 void indirect_result_bad_type(INDIRECT_RESULT int out) SWIFTCALL; // expected-error {{'swift_indirect_result' parameter must have pointer type; type here is 'int'}}
 void indirect_result_single(INDIRECT_RESULT void *out) SWIFTCALL;
 void indirect_result_multiple(INDIRECT_RESULT void *out1, INDIRECT_RESULT void *out2) SWIFTCALL;
 
 void error_result_nonswift(ERROR_RESULT void **error); // expected-error {{'swift_error_result' parameter can only be used with swiftcall calling convention}} expected-error{{'swift_error_result' parameter must follow 'swift_context' parameter}}
 void error_result_bad_position2(int first, ERROR_RESULT void **error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must follow 'swift_context' parameter}}
 void error_result_bad_type(CONTEXT void *context, ERROR_RESULT int error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must have pointer to unqualified pointer type; type here is 'int'}}
 void error_result_bad_type2(CONTEXT void *context, ERROR_RESULT int *error) SWIFTCALL; // expected-error {{'swift_error_result' parameter must have pointer to unqualified pointer type; type here is 'int *'}}
 void error_result_okay(int a, int b, CONTEXT void *context, ERROR_RESULT void **error) SWIFTCALL;
 void error_result_okay(CONTEXT void *context, ERROR_RESULT void **error, void *selfType, char **selfWitnessTable) SWIFTCALL;
 
 void context_nonswift(CONTEXT void *context); // expected-error {{'swift_context' parameter can only be used with swiftcall calling convention}}
 void context_bad_type(CONTEXT int context) SWIFTCALL; // expected-error {{'swift_context' parameter must have pointer type; type here is 'int'}}
 void context_okay(CONTEXT void *context) SWIFTCALL;
 void context_okay(CONTEXT void *context, void *selfType, char **selfWitnessTable) SWIFTCALL;
 
+void async_context_nonswift(ASYNC_CONTEXT void *context); // expected-error {{'swift_async_context' parameter can only be used with swiftasynccall calling convention}}
+void async_context_bad_type(ASYNC_CONTEXT int context) SWIFTASYNCCALL; // expected-error {{'swift_async_context' parameter must have pointer type; type here is 'int'}}
+void async_context_okay(ASYNC_CONTEXT void *context) SWIFTASYNCCALL;
+void async_context_okay(void *someArg, ASYNC_CONTEXT void *context, void *otherArg) SWIFTASYNCCALL;
+
 template <class T> void indirect_result_temp_okay1(INDIRECT_RESULT T *out) SWIFTCALL;
 template <class T> void indirect_result_temp_okay2(INDIRECT_RESULT T out) SWIFTCALL; // expected-note {{candidate template ignored: substitution failure [with T = int]: 'swift_indirect_result' parameter must have pointer type; type here is 'int'}}
 void test_indirect_result_temp(void *out) {
   indirect_result_temp_okay1(out);
   indirect_result_temp_okay2(out);
   indirect_result_temp_okay2(1); // expected-error {{no matching function for call to 'indirect_result_temp_okay2'}}
 }

clang/tools/libclang/CXType.cpp

switch (FD->getCallConv()) {
       TCALLINGCONV(X86VectorCall);
       TCALLINGCONV(AArch64VectorCall);
       TCALLINGCONV(Win64);
       TCALLINGCONV(X86_64SysV);
       TCALLINGCONV(AAPCS);
       TCALLINGCONV(AAPCS_VFP);
       TCALLINGCONV(IntelOclBicc);
       TCALLINGCONV(Swift);
+      TCALLINGCONV(SwiftAsync);
       TCALLINGCONV(PreserveMost);
       TCALLINGCONV(PreserveAll);
     case CC_SpirFunction: return CXCallingConv_Unexposed;
     case CC_OpenCLKernel: return CXCallingConv_Unexposed;
       break;
     }
 #undef TCALLINGCONV
   }

llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h

enum class CallingConv : uint8_t {
   Pascal,
   Thiscall,
   Stdcall,
   Fastcall,
   Clrcall,
   Eabi,
   Vectorcall,
   Regcall,
-  Swift, // Clang-only
+  Swift,      // Clang-only
+  SwiftAsync, // Clang-only
 };
 
 enum class ReferenceKind : uint8_t { None, LValueRef, RValueRef };
 
 enum OutputFlags {
   OF_Default = 0,
   OF_NoCallingConvention = 1,
   OF_NoTagSpecifier = 2,

llvm/lib/Demangle/MicrosoftDemangle.cpp

case 'N':
     return CallingConv::Clrcall;
   case 'O':
   case 'P':
     return CallingConv::Eabi;
   case 'Q':
     return CallingConv::Vectorcall;
   case 'S':
     return CallingConv::Swift;
+  case 'T':
+    return CallingConv::SwiftAsync;
   }
 
   return CallingConv::None;
 }
 
 StorageClass Demangler::demangleVariableStorageClass(StringView &MangledName) {
   assert(MangledName.front() >= '0' && MangledName.front() <= '4');
 

llvm/lib/Demangle/MicrosoftDemangleNodes.cpp

case CallingConv::Vectorcall:
     OS << "__vectorcall";
     break;
   case CallingConv::Clrcall:
     OS << "__clrcall";
     break;
   case CallingConv::Swift:
     OS << "__attribute__((__swiftcall__)) ";
     break;
+  case CallingConv::SwiftAsync:
+    OS << "__attribute__((__swiftasynccall__)) ";
+    break;
   default:
     break;
   }
 }
 
 std::string Node::toString(OutputFlags Flags) const {
   OutputStream OS;
   initializeOutputStream(nullptr, nullptr, OS, 1024);

llvm/test/Demangle/ms-mangle.test

 ; CHECK: static void __cdecl TypedefNewDelete::operator delete[](void *)
 
 ?vector_func@@YQXXZ
 ; CHECK: void __vectorcall vector_func(void)
 
 ?swift_func@@YSXXZ
 ; CHECK: void __attribute__((__swiftcall__)) swift_func(void)
 
+?swift_async_func@@YTXXZ
+; CHECK: void __attribute__((__swiftasynccall__)) swift_async_func(void)
+
 ??$fn_tmpl@$1?extern_c_func@@YAXXZ@@YAXXZ
 ; CHECK: void __cdecl fn_tmpl<&void __cdecl extern_c_func(void)>(void)
 
 ?overloaded_fn@@$$J0YAXXZ
 ; CHECK: extern "C" void __cdecl overloaded_fn(void)
 
 ?f@UnnamedType@@YAXQAPAU<unnamed-type-T1>@S@1@@Z
 ; CHECK: void __cdecl UnnamedType::f(struct UnnamedType::S::<unnamed-type-T1> **const)