[AddressLowering] Look through opaque result type.

A function which returns a value of opaque result type

    func f() -> some P { S() }

has a lowered, substituted signature

    @convention(thin) () -> @out @_opaqueReturnTypeOf("$s4main1fQryF", 0) opaque

featuring an _opaqueReturnTypeOf attr.  The SILFunctionArgument for that
@out result, however, must be of the type that the opaque result
substitutes to in the expansion context of the function.

Author: nate-chandler

lib/SILOptimizer/Mandatory/AddressLowering.cpp

@@ -689,7 +689,9 @@ static unsigned insertIndirectReturnArgs(AddressLoweringState &pass) {
 
   unsigned argIdx = 0;
   for (auto resultTy : pass.loweredFnConv.getIndirectSILResultTypes(typeCtx)) {
-    auto bodyResultTy = pass.function->mapTypeIntoContext(resultTy);
+    auto resultTyInContext = pass.function->mapTypeIntoContext(resultTy);
+    auto bodyResultTy = pass.function->getModule().Types.getLoweredType(
+        resultTyInContext.getASTType(), *pass.function);
     auto var = new (astCtx) ParamDecl(
         SourceLoc(), SourceLoc(), astCtx.getIdentifier("$return_value"),
         SourceLoc(), astCtx.getIdentifier("$return_value"), declCtx);

test/SILOptimizer/address_lowering.sil

@@ -18,6 +18,10 @@ protocol P {
   func foo()
 }
 
+struct S : P {
+  func foo()
+}
+
 enum Optional<T> {
   case none
   case some(T)
@@ -549,6 +553,23 @@ bb0(%0 : @owned $T, %1 : @owned $C):
   return %2 : $(T, C)
 }
 
+// CHECK-LABEL: sil [ossa] @f076_opaqueResult : {{.*}} {
+// CHECK:       {{bb[0-9]+}}([[S_ADDR:%[^,]+]] : $*S):
+// CHECK:         [[GET:%[^,]+]] = function_ref @getT
+// CHECK:         [[TEMP:%[^,]+]] = alloc_stack $S
+// CHECK:         apply [[GET]]<S>([[TEMP]])
+// CHECK:         [[S:%[^,]+]] = load [trivial] [[TEMP]]
+// CHECK:         store [[S]] to [trivial] [[S_ADDR]]
+// CHECK:         dealloc_stack [[TEMP]]
+// CHECK-LABEL: } // end sil function 'f076_opaqueResult'
+// The following getS definition enables use of the type <<@_opaqueReturnTypeOf("$s5Swift4getSQryF", 0) opaque>>
+@_silgen_name("getS") public func getS() -> some P { return S() }
+sil [ossa] @f076_opaqueResult : $@convention(thin) <T> () -> @out @_opaqueReturnTypeOf("$s5Swift4getSQryF", 0) __<T> {
+  %get = function_ref @getT : $@convention(thin) <T> () -> (@out T)
+  %s = apply %get<S>() : $@convention(thin) <T> () -> (@out T)
+  return %s : $S
+}
+
 // CHECK-LABEL: sil [ossa] @f080_optional : $@convention(thin) <T> (@in T) -> @out Optional<T> {
 // CHECK: bb0(%0 : $*Optional<T>, %1 : $*T):
 // CHECK:   [[DATA:%.*]] = init_enum_data_addr %0 : $*Optional<T>, #Optional.some!enumelt