EscapeAnalysis: fix a bug with results in not detecting an escape through an unowned reference.

`ref_to_unowned`  and similar instructions must be checked if the operand/result types are treated as "pointers" in escape analysis.
Fixes a miscompile.

https://bugs.swift.org/browse/SR-15527
rdar://85772200

Author: eeckstein

lib/SILOptimizer/Analysis/EscapeAnalysis.cpp

@@ -202,21 +202,22 @@ SILValue EscapeAnalysis::getPointerBase(SILValue value) {
   case ValueKind::RefToRawPointerInst:
   case ValueKind::RefToBridgeObjectInst:
   case ValueKind::BridgeObjectToRefInst:
+    return cast<SingleValueInstruction>(value)->getOperand(0);
+
   case ValueKind::UnconditionalCheckedCastInst:
+  case ValueKind::UncheckedAddrCastInst:
     // DO NOT use LOADABLE_REF_STORAGE because unchecked references don't have
     // retain/release instructions that trigger the 'default' case.
 #define ALWAYS_OR_SOMETIMES_LOADABLE_CHECKED_REF_STORAGE(Name, ...)            \
   case ValueKind::RefTo##Name##Inst:                                           \
   case ValueKind::Name##ToRefInst:
 #include "swift/AST/ReferenceStorage.def"
-    return cast<SingleValueInstruction>(value)->getOperand(0);
-
-  case ValueKind::UncheckedAddrCastInst: {
-    auto *uac = cast<UncheckedAddrCastInst>(value);
-    SILValue op = uac->getOperand();
+  {
+    auto *svi = cast<SingleValueInstruction>(value);
+    SILValue op = svi->getOperand(0);
     SILType srcTy = op->getType().getObjectType();
     SILType destTy = value->getType().getObjectType();
-    SILFunction *f = uac->getFunction();
+    SILFunction *f = svi->getFunction();
     // If the source and destination of the cast don't agree on being a pointer,
     // we bail. Otherwise we would miss important edges in the connection graph:
     // e.g. loads of non-pointers are ignored, while it could be an escape of

test/SILOptimizer/stack_promotion.sil

@@ -854,3 +854,24 @@ bb1(%4 : $XX):
 bb2(%5 : $Error):
   throw %5 : $Error
 }
+
+final class UnownedLink {
+  @_hasStorage unowned var link: @sil_unowned UnownedLink
+}
+
+// CHECK-LABEL: sil @dont_promote_escaping_through_unowned
+// CHECK:         alloc_ref $UnownedLink
+// CHECK-NOT:     dealloc_ref
+// CHECK-LABEL: } // end sil function 'dont_promote_escaping_through_unowned'
+sil @dont_promote_escaping_through_unowned : $@convention(method) (@guaranteed UnownedLink) -> () {
+bb0(%0 : $UnownedLink):
+  %298 = alloc_ref $UnownedLink
+  %20 = ref_to_unowned %298 : $UnownedLink to $@sil_unowned UnownedLink
+  %44 = ref_element_addr %0 : $UnownedLink, #UnownedLink.link
+  %45 = begin_access [modify] [dynamic] %44 : $*@sil_unowned UnownedLink
+  store %20 to %45 : $*@sil_unowned UnownedLink
+  end_access %45 : $*@sil_unowned UnownedLink
+  strong_release %298 : $UnownedLink
+  %r = tuple ()
+  return %r : $()
+}