[IRGen] Map result to native representation in emitAsyncReturn

rdar://147872231

When an async typed throwing function had a result type that combined multiple fields into a single register, we created invalid IR, that could lead to compiler crashes or in some cases even miscompiles. With this fix we are mapping the result to the native representation before mapping it to the combined result type.

Author: drexin

lib/IRGen/GenCall.cpp

@@ -6346,10 +6346,12 @@ void irgen::emitAsyncReturn(IRGenFunction &IGF, AsyncContextLayout &asyncLayout,
       if (combinedTy->isVoidTy()) {
         assert(result.empty() && "Unexpected result values");
       } else {
+        Explosion native = nativeSchema.mapIntoNative(
+            IGM, IGF, result, funcResultTypeInContext, /*isOutlined*/ false);
         if (auto *structTy = dyn_cast<llvm::StructType>(combinedTy)) {
           llvm::Value *nativeAgg = llvm::UndefValue::get(structTy);
-          for (unsigned i = 0, e = result.size(); i < e; ++i) {
-            llvm::Value *elt = result.claimNext();
+          for (unsigned i = 0, e = native.size(); i < e; ++i) {
+            llvm::Value *elt = native.claimNext();
             auto *nativeTy = structTy->getElementType(i);
             elt = convertForDirectError(IGF, elt, nativeTy,
                                         /*forExtraction*/ false);
@@ -6360,9 +6362,9 @@ void irgen::emitAsyncReturn(IRGenFunction &IGF, AsyncContextLayout &asyncLayout,
           while (!out.empty()) {
             nativeResultsStorage.push_back(out.claimNext());
           }
-        } else if (!result.empty()) {
+        } else if (!native.empty()) {
           auto *converted = convertForDirectError(
-              IGF, result.claimNext(), combinedTy, /*forExtraction*/ false);
+              IGF, native.claimNext(), combinedTy, /*forExtraction*/ false);
           nativeResultsStorage.push_back(converted);
         } else {
           nativeResultsStorage.push_back(llvm::UndefValue::get(combinedTy));

test/IRGen/typed_throws.swift

@@ -349,3 +349,13 @@ func callSmallErrorLargerResult() {
     }
   }
 }
+
+struct SomeStruct {
+    let x: Int
+    let y: UInt32
+    let z: UInt32
+}
+
+func someFunc() async throws(SmallError) -> SomeStruct {
+    SomeStruct(x: 42, y: 23, z: 25)
+}