SILOptimizer: replace existential archetypes with concrete types in witness_method instructions

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/CMakeLists.txt

@@ -38,4 +38,5 @@ swift_compiler_sources(Optimizer
   SimplifyTuple.swift
   SimplifyTupleExtract.swift
   SimplifyUncheckedEnumData.swift
-  SimplifyValueToBridgeObject.swift)
+  SimplifyValueToBridgeObject.swift
+  SimplifyWitnessMethod.swift)

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyWitnessMethod.swift

@@ -0,0 +1,48 @@
+//===--- SimplifyWitnessMethod.swift --------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import AST
+import SIL
+
+extension WitnessMethodInst : Simplifiable, SILCombineSimplifiable {
+  func simplify(_ context: SimplifyContext) {
+    _ = tryReplaceExistentialArchetype(of: self, context)
+  }
+}
+
+/// If the witness_method operates on an existential archetype (`@opened("...")`) and the concrete
+/// type is known, replace the existential archetype with the concrete type.
+/// For example:
+/// ```
+///   %3 = witness_method $@opened("...", P) Self, #P.foo, %2
+/// ```
+/// ->
+/// ```
+///   %3 = witness_method $ConcreteType, #P.foo, %2
+/// ```
+private func tryReplaceExistentialArchetype(of witnessMethod: WitnessMethodInst, _ context: SimplifyContext) -> Bool {
+  guard let concreteType = witnessMethod.concreteTypeOfDependentExistentialArchetype else {
+    return false
+  }
+  let conf = concreteType.checkConformance(to: witnessMethod.lookupProtocol)
+  guard conf.isValid else {
+    return false
+  }
+
+  let builder = Builder(before: witnessMethod, context)
+  let newWmi = builder.createWitnessMethod(lookupType: concreteType,
+                                           conformance: conf,
+                                           member: witnessMethod.member,
+                                           methodType: witnessMethod.type)
+  witnessMethod.replace(with: newWmi, context)
+  return true
+}

SwiftCompilerSources/Sources/Optimizer/PassManager/PassRegistration.swift

@@ -119,6 +119,7 @@ private func registerSwiftPasses() {
   registerForSILCombine(ClassifyBridgeObjectInst.self, { run(ClassifyBridgeObjectInst.self, $0) })
   registerForSILCombine(PointerToAddressInst.self,  { run(PointerToAddressInst.self, $0) })
   registerForSILCombine(UncheckedEnumDataInst.self, { run(UncheckedEnumDataInst.self, $0) })
+  registerForSILCombine(WitnessMethodInst.self,     { run(WitnessMethodInst.self, $0) })
   registerForSILCombine(UnconditionalCheckedCastInst.self, { run(UnconditionalCheckedCastInst.self, $0) })
   registerForSILCombine(ApplyInst.self,             { run(ApplyInst.self, $0) })
   registerForSILCombine(TryApplyInst.self,          { run(TryApplyInst.self, $0) })

include/swift/SILOptimizer/PassManager/Passes.def

@@ -539,6 +539,7 @@ SWIFT_SILCOMBINE_PASS(DestructureTupleInst)
 SWIFT_SILCOMBINE_PASS(PointerToAddressInst)
 SWIFT_SILCOMBINE_PASS(TypeValueInst)
 SWIFT_SILCOMBINE_PASS(UncheckedEnumDataInst)
+SWIFT_SILCOMBINE_PASS(WitnessMethodInst)
 SWIFT_SILCOMBINE_PASS_WITH_LEGACY(UnconditionalCheckedCastInst)
 SWIFT_SILCOMBINE_PASS_WITH_LEGACY(ApplyInst)
 SWIFT_SILCOMBINE_PASS_WITH_LEGACY(TryApplyInst)

test/SILOptimizer/sil_combine.sil

@@ -3447,10 +3447,10 @@ class ClientSocket : Socket {
 }
 
 // CHECK-LABEL: static_existential
-// CHECK:bb0:
-// CHECK:  [[META:%.*]] = metatype $@thick ClientSocket.Type
-// CHECK:  [[WM:%.*]] = witness_method $ClientSocket
-// CHECK:  try_apply [[WM]]<ClientSocket>([[META]])
+// CHECK:       bb0:
+// CHECK-DAG:    [[META:%.*]] = metatype $@thick ClientSocket.Type
+// CHECK-DAG:    [[WM:%.*]] = witness_method $ClientSocket
+// CHECK:        try_apply [[WM]]<ClientSocket>([[META]])
 sil @static_existential : $@convention(thin) () -> (Builtin.Int32, @error MyErrorType) {
 bb0:
   %0 = metatype $@thick ClientSocket.Type

test/SILOptimizer/simplify_witness_method.sil

@@ -0,0 +1,41 @@
+// RUN: %target-sil-opt %s -simplification -simplify-instruction=witness_method | %FileCheck %s
+
+import Swift
+import Builtin
+
+protocol P {
+  func foo()
+}
+
+struct S: P {
+  var x: Int
+
+  func foo()
+}
+
+// CHECK-LABEL: sil [ossa] @replace_archetype :
+// CHECK:        = witness_method $S, #P.foo : <Self where Self : P> (Self) -> () -> () : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> ()
+// CHECK:       } // end sil function 'replace_archetype'
+sil [ossa] @replace_archetype : $@convention(thin) () -> () {
+bb0:
+  %0 = metatype $@thick S.Type
+  %1 = init_existential_metatype %0, $@thick P.Type
+  %2 = open_existential_metatype %1 to $@thick (@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self).Type
+  %3 = witness_method $@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self, #P.foo, %2 : $@thick (@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self).Type : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> ()
+  %4 = apply %3<@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self>(%2) : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> ()
+  %5 = tuple ()
+  return %5
+}
+
+// CHECK-LABEL: sil [ossa] @dont_replace_archetype_unknown_concrete_type :
+// CHECK:        = witness_method $@opened
+// CHECK:       } // end sil function 'dont_replace_archetype_unknown_concrete_type'
+sil [ossa] @dont_replace_archetype_unknown_concrete_type : $@convention(thin) (@thick any P.Type) -> () {
+bb0(%0 : $@thick any P.Type):
+  %2 = open_existential_metatype %0 to $@thick (@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self).Type
+  %3 = witness_method $@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self, #P.foo, %2 : $@thick (@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self).Type : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> ()
+  %4 = apply %3<@opened("82105EE0-DCB0-11E5-865D-C8E0EB309913", P) Self>(%2) : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> ()
+  %5 = tuple ()
+  return %5
+}
+