From 41dd3dc453a1cd8df099a7d28fb80d2632bcc92e Mon Sep 17 00:00:00 2001
From: Erik Eckstein <eeckstein@apple.com>
Date: Tue, 24 Dec 2024 11:56:34 +0100
Subject: [PATCH] DeadObjectElimination: handle OSSA instructions when
 analyzing class destructors

Handle typical patterns which are generated by SILGen.
---
 lib/SIL/Utils/InstructionUtils.cpp            |  1 +
 .../Transforms/DeadObjectElimination.cpp      |  4 ++
 test/SILOptimizer/dead_alloc_elim_ossa.sil    | 38 +++++++++++++++++++
 3 files changed, 43 insertions(+)

diff --git a/lib/SIL/Utils/InstructionUtils.cpp b/lib/SIL/Utils/InstructionUtils.cpp
index 60c1af0df33f8..f7af093151587 100644
--- a/lib/SIL/Utils/InstructionUtils.cpp
+++ b/lib/SIL/Utils/InstructionUtils.cpp
@@ -172,6 +172,7 @@ SILValue swift::stripCasts(SILValue v) {
     if (auto *svi = dyn_cast<SingleValueInstruction>(v)) {
       if (isIdentityPreservingRefCast(svi) ||
           isa<UncheckedTrivialBitCastInst>(v) || isa<MarkDependenceInst>(v) ||
+          isa<UncheckedOwnershipConversionInst>(v) ||
           isa<BeginAccessInst>(v)) {
         v = cast<SingleValueInstruction>(v)->getOperand(0);
         continue;
diff --git a/lib/SILOptimizer/Transforms/DeadObjectElimination.cpp b/lib/SILOptimizer/Transforms/DeadObjectElimination.cpp
index feb7d98ca3bb1..6766f7b5ae5a4 100644
--- a/lib/SILOptimizer/Transforms/DeadObjectElimination.cpp
+++ b/lib/SILOptimizer/Transforms/DeadObjectElimination.cpp
@@ -204,6 +204,10 @@ static DestructorEffects doesDestructorHaveSideEffects(AllocRefInstBase *ARI) {
         continue;
       }
 
+      if (isa<BeginBorrowInst>(I) || isa<EndBorrowInst>(I) || isa<EndLifetimeInst>(I)) {
+        continue;
+      }
+
       // dealloc_ref on self can be ignored, but dealloc_ref on anything else
       // cannot be eliminated.
       if (auto *DeallocRef = dyn_cast<DeallocRefInst>(&I)) {
diff --git a/test/SILOptimizer/dead_alloc_elim_ossa.sil b/test/SILOptimizer/dead_alloc_elim_ossa.sil
index 4a7f6846765fe..ed31b2c4eab7f 100644
--- a/test/SILOptimizer/dead_alloc_elim_ossa.sil
+++ b/test/SILOptimizer/dead_alloc_elim_ossa.sil
@@ -28,6 +28,11 @@ class ArrayStorage {
   init()
 }
 
+class Kl2 {
+  @_hasStorage var i: Int
+}
+
+
 protocol P { }
 struct X : P { }
 
@@ -65,6 +70,19 @@ bb0(%0 : @owned $NontrivialDestructor):
   return %7 : $()
 }
 
+sil [ossa] @$s4main3Kl2CfD : $@convention(method) (@owned Kl2) -> () {
+bb0(%0 : @owned $Kl2):
+  %1 = begin_borrow %0
+  %2 = unchecked_ref_cast %1 to $Builtin.NativeObject
+  %3 = unchecked_ownership_conversion %2, @guaranteed to @owned
+  end_borrow %1
+  end_lifetime %0
+  %6 = unchecked_ref_cast %3 to $Kl2
+  dealloc_ref %6
+  %8 = tuple ()
+  return %8
+}
+
 sil @ptr_user : $@convention(thin) (Builtin.NativeObject) -> ()
 sil @int_user : $@convention(thin) (Builtin.Int32) -> ()
 
@@ -541,3 +559,23 @@ bb0(%0 : @owned $_ContiguousArrayStorage<Element>):
   return %15 : $()
 }
 
+// CHECK-LABEL: sil [ossa] @dead_alloc_with_complex_ossa_destructor
+// CHECK-NOT:     alloc_ref
+// CHECK:       } // end sil function 'dead_alloc_with_complex_ossa_destructor'
+sil [ossa] @dead_alloc_with_complex_ossa_destructor : $@convention(thin) () -> Int {
+bb0:
+  %0 = alloc_ref $Kl2
+  %1 = move_value [lexical] %0
+  %2 = end_init_let_ref %1
+  %3 = begin_borrow %2
+  %4 = integer_literal $Builtin.Int64, 27
+  %5 = struct $Int (%4)
+  %6 = ref_element_addr %3, #Kl2.i
+  store %5 to [trivial] %6
+  end_borrow %3
+  %9 = move_value [lexical] [var_decl] %2
+  debug_value %9, let, name "k"
+  destroy_value %9
+  return %5
+}
+