Lower imported C structs and unions as addressable-for-dependencies.

C code is highly likely to want to use pointers as references between dependent
structs, and we would like to be able to readily map these to lifetime-dependent
Swift values. Making C types addressable-for-dependencies ensures that any function
producing a dependency on such a value receives a stable in-memory address for that
value, allowing borrows and inout accesses to always be representable as pointers.

rdar://153648393

Author: jckarter

lib/SIL/IR/TypeLowering.cpp

@@ -2537,6 +2537,11 @@ namespace {
           // that a union contains a pointer.
           if (recordDecl->isOrContainsUnion())
             properties.setIsOrContainsRawPointer();
+            
+          // Treat imported C structs and unions as addressable-for-dependencies
+          // so that Swift lifetime dependencies are more readily interoperable
+          // with pointers in C used for similar purposes.
+          properties.setAddressableForDependencies();
         }
       }
 

test/Interop/Cxx/class/nonescapable-lifetimebound.swift

@@ -116,20 +116,20 @@ namespace NS {
 }
 
 // CHECK: sil [clang makeOwner] {{.*}}: $@convention(c) () -> Owner
-// CHECK: sil [clang getView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
-// CHECK: sil [clang getViewFromFirst] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
-// CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow 0, borrow 1) @owned View
+// CHECK: sil [clang getView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow address_for_deps 0) @owned View
+// CHECK: sil [clang getViewFromFirst] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow address_for_deps 0) @owned View
+// CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow address_for_deps 0, borrow address_for_deps 1) @owned View
 // CHECK: sil [clang Owner.handOutView] {{.*}} : $@convention(cxx_method) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
 // CHECK: sil [clang Owner.handOutView2] {{.*}} : $@convention(cxx_method) (View, @in_guaranteed Owner) -> @lifetime(borrow 1) @owned View
 // CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (View, View) -> @lifetime(copy 0, copy 1) @owned View
 // CHECK: sil [clang View.init] {{.*}} : $@convention(c) () -> @lifetime(immortal) @out View
 // CHECK: sil [clang OtherView.init] {{.*}} : $@convention(c) (View) -> @lifetime(copy 0) @out OtherView
 // CHECK: sil [clang returnsImmortal] {{.*}} : $@convention(c) () -> @lifetime(immortal) @owned View
 // CHECK: sil [clang copyView] {{.*}} : $@convention(c) (View, @lifetime(copy 0) @inout View) -> ()
-// CHECK: sil [clang getCaptureView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned CaptureView
+// CHECK: sil [clang getCaptureView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow address_for_deps 0) @owned CaptureView
 // CHECK: sil [clang CaptureView.captureView] {{.*}} : $@convention(cxx_method) (View, @lifetime(copy 0) @inout CaptureView) -> ()
 // CHECK: sil [clang CaptureView.handOut] {{.*}} : $@convention(cxx_method) (@lifetime(copy 1) @inout View, @in_guaranteed CaptureView) -> ()
-// CHECK: sil [clang NS.getView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
+// CHECK: sil [clang NS.getView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow address_for_deps 0) @owned View
 
 //--- test.swift
 

test/SILGen/Inputs/clang_records_addressable_for_dependencies.h

@@ -0,0 +1,2 @@
+struct CStruct { int x; int y; };
+union CUnion { int x; int y; };

test/SILGen/clang_records_addressable_for_dependencies.swift

@@ -0,0 +1,16 @@
+// RUN: %target-swift-emit-silgen -import-objc-header %S/Inputs/clang_records_addressable_for_dependencies.h -enable-experimental-feature Lifetimes %s | %FileCheck %s
+
+// REQUIRES: swift_feature_Lifetimes
+
+struct Dependent: ~Escapable {
+	@_lifetime(immortal)
+	init() { fatalError() }
+}
+
+// CHECK-LABEL: sil {{.*}} @${{.*}}12dependenceOn7cStruct{{.*}} : $@convention(thin) (@in_guaranteed CStruct)
+@_lifetime(cStruct)
+func dependenceOn(cStruct: CStruct) -> Dependent { fatalError() }
+
+// CHECK-LABEL: sil {{.*}} @${{.*}}12dependenceOn6cUnion{{.*}} : $@convention(thin) (@in_guaranteed CUnion)
+@_lifetime(cUnion)
+func dependenceOn(cUnion: CUnion) -> Dependent { fatalError() }