AliasAnalysis: handle destroy_value [dead_end] in computeMemoryEffect

We don't have to take deinit effects into acount for a `destroy_value [dead_end]`.
Such destroys are lowered to no-ops and will not call any deinit.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Analysis/AliasAnalysis.swift

@@ -309,6 +309,11 @@ struct AliasAnalysis {
       if destroy.destroyedValue.type.isNoEscapeFunction {
         return .noEffects
       }
+      if destroy.isDeadEnd {
+        // We don't have to take deinit effects into acount for a `destroy_value [dead_end]`.
+        // Such destroys are lowered to no-ops and will not call any deinit.
+        return .noEffects
+      }
       return defaultEffects(of: destroy, on: memLoc)
 
     default:

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -506,6 +506,11 @@ final public class UnmanagedAutoreleaseValueInst : RefCountingInst {}
 
 final public class DestroyValueInst : Instruction, UnaryInstruction {
   public var destroyedValue: Value { operand.value }
+
+  /// True if this `destroy_value` is inside a dead-end block is only needed to formally
+  /// end the lifetime of its operand.
+  /// Such `destroy_value` instructions are lowered to no-ops.
+  public var isDeadEnd: Bool { bridged.DestroyValueInst_isDeadEnd() }
 }
 
 final public class DestroyAddrInst : Instruction, UnaryInstruction {

include/swift/SIL/SILBridging.h

@@ -951,6 +951,7 @@ struct BridgedInstruction {
 
   BRIDGED_INLINE SwiftInt ProjectBoxInst_fieldIndex() const;
   BRIDGED_INLINE bool EndCOWMutationInst_doKeepUnique() const;
+  BRIDGED_INLINE bool DestroyValueInst_isDeadEnd() const;
   BRIDGED_INLINE SwiftInt EnumInst_caseIndex() const;
   BRIDGED_INLINE SwiftInt UncheckedEnumDataInst_caseIndex() const;
   BRIDGED_INLINE SwiftInt InitEnumDataAddrInst_caseIndex() const;

include/swift/SIL/SILBridgingImpl.h

@@ -1111,6 +1111,10 @@ bool BridgedInstruction::EndCOWMutationInst_doKeepUnique() const {
   return getAs<swift::EndCOWMutationInst>()->doKeepUnique();
 }
 
+bool BridgedInstruction::DestroyValueInst_isDeadEnd() const {
+  return getAs<swift::DestroyValueInst>()->isDeadEnd();
+}
+
 SwiftInt BridgedInstruction::EnumInst_caseIndex() const {
   return getAs<swift::EnumInst>()->getCaseIndex();
 }

test/SILOptimizer/mem-behavior.sil

@@ -1009,6 +1009,36 @@ bb0 (%0 : $*C):
   return %2 : $()
 }
 
+// CHECK-LABEL: @test_destroy_value_with_effects
+// CHECK:       PAIR #1.
+// CHECK-NEXT:     destroy_value %0 : $X
+// CHECK-NEXT:     %2 = ref_element_addr %1 : $X, #X.x
+// CHECK-NEXT:   r=1,w=1
+sil [ossa] @test_destroy_value_with_effects : $@convention(thin) (@owned X) -> () {
+bb0 (%0 : @owned $X):
+  %1 = begin_borrow %0 : $X
+  %2 = ref_element_addr %1 : $X, #X.x
+  fix_lifetime %2 : $*X
+  end_borrow %1 : $X
+  destroy_value %0 : $X
+  unreachable
+}
+
+// CHECK-LABEL: @test_deadend_destroy_value
+// CHECK:       PAIR #1.
+// CHECK-NEXT:      destroy_value [dead_end] %0 : $X
+// CHECK-NEXT:      %2 = ref_element_addr %1 : $X, #X.x
+// CHECK-NEXT:    r=0,w=0
+sil [ossa] @test_deadend_destroy_value : $@convention(thin) (@owned X) -> () {
+bb0 (%0 : @owned $X):
+  %1 = begin_borrow %0 : $X
+  %2 = ref_element_addr %1 : $X, #X.x
+  fix_lifetime %2 : $*X
+  end_borrow %1 : $X
+  destroy_value [dead_end] %0 : $X
+  unreachable
+}
+
 // CHECK-LABEL: @test_copy_value
 // CHECK: PAIR #1.
 // CHECK-NEXT:     %2 = copy_value %1 : $C