[SystemZ] Support Swift calling convention

[bryanpkc]

Summary

Port rL265324 to SystemZ to allow using the 'swiftcall' attribute on that architecture.

Depends on D19414.

[rjmccall]

LGTM.

[uweigand]

LGTM.

[bryanpkc]

Thank you for the reviews.

lib/Basic/Targets.cpp

public:
   bool hasFeature(StringRef Feature) const override {
     return llvm::StringSwitch<bool>(Feature)
         .Case("systemz", true)
         .Case("htm", HasTransactionalExecution)
         .Case("vx", HasVector)
         .Default(false);
   }
 
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_C:
+    case CC_Swift:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
+  }
+
   StringRef getABI() const override {
     if (HasVector)
       return "vector";
     return "";
   }
 
   bool useFloat128ManglingForLongDouble() const override {
     return true;

lib/CodeGen/TargetInfo.cpp

 }
 
 //===----------------------------------------------------------------------===//
 // SystemZ ABI Implementation
 //===----------------------------------------------------------------------===//
 
 namespace {
 
-class SystemZABIInfo : public ABIInfo {
+class SystemZABIInfo : public SwiftABIInfo {
   bool HasVector;
 
 public:
   SystemZABIInfo(CodeGenTypes &CGT, bool HV)
-    : ABIInfo(CGT), HasVector(HV) {}
+    : SwiftABIInfo(CGT), HasVector(HV) {}
 
   bool isPromotableIntegerType(QualType Ty) const;
   bool isCompoundType(QualType Ty) const;
   bool isVectorArgumentType(QualType Ty) const;
   bool isFPArgumentType(QualType Ty) const;
   QualType GetSingleElementType(QualType Ty) const;
 
   ABIArgInfo classifyReturnType(QualType RetTy) const;
   ABIArgInfo classifyArgumentType(QualType ArgTy) const;
 
   void computeInfo(CGFunctionInfo &FI) const override {
     if (!getCXXABI().classifyReturnType(FI))
       FI.getReturnInfo() = classifyReturnType(FI.getReturnType());
     for (auto &I : FI.arguments())
       I.info = classifyArgumentType(I.type);
   }
 
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
+
+  bool shouldPassIndirectlyForSwift(CharUnits totalSize,
+                                    ArrayRef<llvm::Type*> scalars,
+                                    bool asReturnValue) const override {
+    return occupiesMoreThan(CGT, scalars, /*total*/ 4);
+  }
 };
 
 class SystemZTargetCodeGenInfo : public TargetCodeGenInfo {
 public:
   SystemZTargetCodeGenInfo(CodeGenTypes &CGT, bool HasVector)
     : TargetCodeGenInfo(new SystemZABIInfo(CGT, HasVector)) {}
 };