Teach the swift calling convention about _Atomic types

[aschwaighofer]

Summary

rdar://67351073

[aschwaighofer]

Try to sooth clang-tidy

[rjmccall]

Please do this as a very late check rather than the first check.

You need to check for extra atomic padding. If there's any difference between the sizes of the atomic type and its element, just add it as opaque data.

[aschwaighofer]

Respect atomic padding.

[rjmccall]

Thanks, LGTM.

clang/lib/CodeGen/SwiftCallingConv.cpp

 }
 
 static CharUnits getTypeAllocSize(CodeGenModule &CGM, llvm::Type *type) {
   return CharUnits::fromQuantity(CGM.getDataLayout().getTypeAllocSize(type));
 }
 
 void SwiftAggLowering::addTypedData(QualType type, CharUnits begin) {
   // Deal with various aggregate types as special cases:
+  // Atomic types.
+  if (const auto *atomicType = type->getAs<AtomicType>()) {
+    addTypedData(atomicType->getValueType(), begin);
 
     // Record types.
-  if (auto recType = type->getAs<RecordType>()) {
+  } else if (const auto *recType = type->getAs<RecordType>()) {
     addTypedData(recType->getDecl(), begin);
 
   // Array types.
   } else if (type->isArrayType()) {
     // Incomplete array types (flexible array members?) don't provide
     // data to lay out, and the other cases shouldn't be possible.
     auto arrayType = CGM.getContext().getAsConstantArrayType(type);
     if (!arrayType) return;

clang/test/CodeGen/64bit-swiftcall.c

 // At one point, we emitted lifetime.ends without a matching lifetime.start for
 // CoerceAndExpanded args. Since we're not performing optimizations, neither
 // intrinsic should be emitted.
 // CHECK-LABEL: define void @no_lifetime_markers
 void no_lifetime_markers() {
   // CHECK-NOT: call void @llvm.lifetime.
   take_int5(return_int5());
 }
+
+typedef struct {
+  unsigned long long a;
+  unsigned long long b;
+} double_word;
+
+typedef struct {
+  _Atomic(double_word) a;
+} atomic_double_word;
+
+// CHECK-LABEL: use_atomic(i64 %0, i64 %1)
+SWIFTCALL void use_atomic(atomic_double_word a) {}