[MoveOnly] Fix consumption of opened existentials.

Enable walking into `TypeOffsetSizePair`s from an existential into an
archetype.  And set the access kind on `open_existential_addr`
instructions which are the sources of rewritten `copy_addr`s to mutable.

rdar://141279635

Author: nate-chandler

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -3430,6 +3430,10 @@ void MoveOnlyAddressCheckerPImpl::rewriteUses(
       auto accessPath = AccessPathWithBase::computeInScope(copy->getSrc());
       if (auto *access = dyn_cast_or_null<BeginAccessInst>(accessPath.base))
         access->setAccessKind(SILAccessKind::Modify);
+      if (auto *oeai =
+              dyn_cast_or_null<OpenExistentialAddrInst>(copy->getSrc())) {
+        oeai->setAccessKind(OpenedExistentialAccess::Mutable);
+      }
       copy->setIsTakeOfSrc(IsTake);
       continue;
     }

lib/SILOptimizer/Mandatory/MoveOnlyTypeUtils.cpp

@@ -127,6 +127,16 @@ TypeOffsetSizePair::walkOneLevelTowardsChild(
     llvm_unreachable("Not a child of this enum?!");
   }
 
+  if (ancestorType.isExistentialType()) {
+    assert(childType);
+    auto childArchetypeType =
+        childType.getASTType()->getAs<ExistentialArchetypeType>();
+    assert(childArchetypeType);
+    assert(childArchetypeType->getExistentialType()->getCanonicalType() ==
+           ancestorType.getASTType());
+    return {{ancestorOffsetSize, childType}};
+  }
+
   llvm_unreachable("Hit a leaf type?! Should have handled it earlier");
 }
 

validation-test/SILOptimizer/rdar141279635.swift

@@ -0,0 +1,21 @@
+// RUN: %target-build-swift %s
+
+protocol P: ~Copyable {
+    var property: Bool { get }
+    consuming func function()
+}
+
+struct S: P, ~Copyable {
+    var property: Bool { false }
+    consuming func function() {}
+}
+
+func g(s: consuming any P & ~Copyable) {
+    let s = s
+    s.function()
+}
+
+func f() {
+    let s = S()
+    g(s: s)
+}