[OpaqueValues] Emit weak copies.

In opaque values mode, emit the new weak copy instructions to convert as
follows:

strong_copy_weak_value: `@owned $sil_weak T?` -> `@owned $T?`
weak_copy_value: `@owned $T?` -> `@owned $@sil_weak T?`

Doing so is necessary in opaque values mode where it is needed to deal
with weak values directly rather than indirectly via `load_weak`s and
`store_weak`s.

Author: nate-chandler

lib/SILGen/SILGenLValue.cpp

@@ -4414,9 +4414,18 @@ ManagedValue SILGenFunction::emitConversionToSemanticRValue(
   switch (swiftStorageType->getOwnership()) {
   case ReferenceOwnership::Strong:
     llvm_unreachable("strong reference storage type should be impossible");
-#define NEVER_LOADABLE_CHECKED_REF_STORAGE(Name, ...) \
-  case ReferenceOwnership::Name: \
-    /* Address-only storage types are handled with their underlying type. */ \
+#define NEVER_LOADABLE_CHECKED_REF_STORAGE(Name, ...)                          \
+  case ReferenceOwnership::Name:                                               \
+    if (!useLoweredAddresses()) {                                              \
+      auto refTy = src.getType();                                              \
+      auto ty = refTy.getReferenceStorageReferentType();                       \
+      assert(ty);                                                              \
+      assert(ty.getOptionalObjectType());                                      \
+      (void)ty;                                                                \
+      /* Copy the weak value, opening the @sil_weak box. */                    \
+      return B.createStrongCopy##Name##Value(loc, src);                        \
+    }                                                                          \
+    /* Address-only storage types are handled with their underlying type. */   \
     llvm_unreachable("address-only pointers are handled elsewhere");
 #define ALWAYS_OR_SOMETIMES_LOADABLE_CHECKED_REF_STORAGE(Name, ...)            \
   case ReferenceOwnership::Name:                                               \
@@ -4697,11 +4706,26 @@ SILValue SILGenFunction::emitConversionFromSemanticValue(SILLocation loc,
   }
 
   auto swiftStorageType = storageType.castTo<ReferenceStorageType>();
+  if (!useLoweredAddresses() && storageType.isAddressOnly(F)) {
+    switch (swiftStorageType->getOwnership()) {
+      case ReferenceOwnership::Strong:
+        llvm_unreachable("strong reference storage type should be impossible");
+      case ReferenceOwnership::Unmanaged:
+        llvm_unreachable("unimplemented");
+      case ReferenceOwnership::Weak: {
+        auto value = B.createWeakCopyValue(loc, semanticValue);
+        B.emitDestroyValueOperation(loc, semanticValue);
+        return value;
+      }
+      case ReferenceOwnership::Unowned:
+        llvm_unreachable("unimplemented");
+    }
+  }
   switch (swiftStorageType->getOwnership()) {
   case ReferenceOwnership::Strong:
     llvm_unreachable("strong reference storage type should be impossible");
-#define NEVER_LOADABLE_CHECKED_REF_STORAGE(Name, ...) \
-  case ReferenceOwnership::Name: \
+#define NEVER_LOADABLE_CHECKED_REF_STORAGE(Name, ...)                          \
+  case ReferenceOwnership::Name:                                               \
     llvm_unreachable("address-only types are never loadable");
 #define ALWAYS_LOADABLE_CHECKED_REF_STORAGE(Name, ...) \
   case ReferenceOwnership::Name: { \

test/SILGen/opaque_values_silgen.swift

@@ -699,3 +699,19 @@ func FormClassKeyPath() {
 func getInout(_ i: inout MyInt) -> Int {
   return i[keyPath: \MyInt.int]
 }
+// CHECK-LABEL: sil {{.*}}[ossa] @$s20opaque_values_silgen7WeakBoxV1txSgvg : {{.*}} {
+// CHECK:       bb0([[INSTANCE:%[^,]+]] :
+// CHECK:         [[WEAK_OPTIONAL:%[^,]+]] = struct_extract [[INSTANCE]]
+// CHECK:         [[STRONG_OPTIONAL:%[^,]+]] = strong_copy_weak_value [[WEAK_OPTIONAL]]
+// CHECK:         return [[STRONG_OPTIONAL]]
+// CHECK-LABEL: } // end sil function '$s20opaque_values_silgen7WeakBoxV1txSgvg'
+// CHECK-LABEL: sil {{.*}}[ossa] @$s20opaque_values_silgen7WeakBoxV1tACyxGxSg_tcfC : {{.*}} {
+// CHECK:       bb0([[STRONG_OPTIONAL:%[^,]+]] :
+// CHECK:         [[WEAK_OPTIONAL:%[^,]+]] = weak_copy_value [[STRONG_OPTIONAL]]
+// CHECK:         destroy_value [[STRONG_OPTIONAL]]
+// CHECK:         [[INSTANCE:%[^,]+]] = struct $WeakBox<T> ([[WEAK_OPTIONAL]] :
+// CHECK:         return [[INSTANCE]]
+// CHECK-LABEL: } // end sil function '$s20opaque_values_silgen7WeakBoxV1tACyxGxSg_tcfC'
+struct WeakBox<T : AnyObject> {
+  weak var t: T?
+}