Optimizer: simplify unconditional_checked_cast to existential metatypes.

eeckstein · eeckstein · commit 35097b5a71fa · 2025-03-07T15:59:33.000+01:00
Replace `unconditional_checked_cast` to an existential metatype with an `init_existential_metatype`, it the source is a conforming type.
Note that init_existential_metatype is better than unconditional_checked_cast because it does not need to do any runtime casting.
diff --git a/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyCheckedCast.swift b/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyCheckedCast.swift
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import SIL
+import AST
 
 extension CheckedCastAddrBranchInst : OnoneSimplifiable {
   func simplify(_ context: SimplifyContext) {
@@ -53,3 +54,42 @@ private extension CheckedCastAddrBranchInst {
     context.erase(instruction: self)
   }
 }
+
+extension UnconditionalCheckedCastInst : Simplifiable, SILCombineSimplifiable {
+  func simplify(_ context: SimplifyContext) {
+    tryOptimizeCastToExistentialMetatype(context)
+  }
+}
+
+private extension UnconditionalCheckedCastInst {
+  // Replace
+  //     %1 = unconditional_checked_cast %0 : $@thick T.Type to any P.Type
+  // with
+  //     %1 = init_existential_metatype %0 : $@thick S.Type, $@thick any P.Type
+  // if type T conforms to protocol P.
+  // Note that init_existential_metatype is better than unconditional_checked_cast because it does not need
+  // to do any runtime casting.
+  func tryOptimizeCastToExistentialMetatype(_ context: SimplifyContext) {
+    guard targetFormalType.isExistentialMetatypeType,
+          sourceFormalType.isMetatypeType,
+          !sourceFormalType.isExistentialMetatypeType
+    else {
+      return
+    }
+    
+    let instanceTy = targetFormalType.instanceTypeOfMetatype
+    guard let nominal = instanceTy.anyNominal,
+          let proto = nominal as? ProtocolDecl
+    else {
+      return
+    }
+    let conformance = sourceFormalType.instanceTypeOfMetatype.checkConformance(to: proto)
+    guard conformance.isValid else {
+      return
+    }
+    
+    let builder = Builder(before: self, context)
+    let iemt = builder.createInitExistentialMetatype(metatype: operand.value, existentialType: self.type, conformances: [conformance])
+    self.replace(with: iemt, context)
+  }   
+}
diff --git a/SwiftCompilerSources/Sources/Optimizer/PassManager/PassRegistration.swift b/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(UnconditionalCheckedCastInst.self, { run(UnconditionalCheckedCastInst.self, $0) })
 
   // Test passes
   registerPass(aliasInfoDumper, { aliasInfoDumper.run($0) })
diff --git a/include/swift/SILOptimizer/PassManager/Passes.def b/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_WITH_LEGACY(UnconditionalCheckedCastInst)
 
 #undef IRGEN_PASS
 #undef SWIFT_MODULE_PASS
diff --git a/lib/SILOptimizer/SILCombiner/SILCombiner.h b/lib/SILOptimizer/SILCombiner/SILCombiner.h
@@ -266,8 +266,6 @@ class SILCombiner :
   SILInstruction *visitEndCOWMutationInst(EndCOWMutationInst *URCI);
   SILInstruction *visitUncheckedRefCastAddrInst(UncheckedRefCastAddrInst *URCI);
   SILInstruction *visitBridgeObjectToRefInst(BridgeObjectToRefInst *BORI);
-  SILInstruction *visitUnconditionalCheckedCastInst(
-                    UnconditionalCheckedCastInst *UCCI);
   SILInstruction *
   visitUnconditionalCheckedCastAddrInst(UnconditionalCheckedCastAddrInst *UCCAI);
   SILInstruction *visitRawPointerToRefInst(RawPointerToRefInst *RPTR);
diff --git a/lib/SILOptimizer/SILCombiner/SILCombinerCastVisitors.cpp b/lib/SILOptimizer/SILCombiner/SILCombinerCastVisitors.cpp
@@ -516,7 +516,7 @@ SILInstruction *SILCombiner::visitUnconditionalCheckedCastAddrInst(
 
 SILInstruction *
 SILCombiner::
-visitUnconditionalCheckedCastInst(UnconditionalCheckedCastInst *UCCI) {
+legacyVisitUnconditionalCheckedCastInst(UnconditionalCheckedCastInst *UCCI) {
   CastOpt.optimizeUnconditionalCheckedCastInst(UCCI);
   if (UCCI->isDeleted()) {
     MadeChange = true;
diff --git a/test/SILOptimizer/sil_combine_uncheck.sil b/test/SILOptimizer/sil_combine_uncheck.sil
@@ -15,16 +15,6 @@ class D : C {
 class E {
 }
 
-// CHECK-LABEL: sil @test_unconditional_checked_cast
-// CHECK: bb0
-// CHECK-NEXT: unchecked_ref_cast
-// CHECK-NEXT: return
-sil @test_unconditional_checked_cast : $@convention(thin) <T_0_0, T_0_1> (RawBuffer) -> HeapBufferStorage<T_0_0, T_0_1> {
-bb0(%0 : $RawBuffer):
-  %3 = unconditional_checked_cast %0 : $RawBuffer to HeapBufferStorage<T_0_0, T_0_1>
-  return %3 : $HeapBufferStorage<T_0_0, T_0_1>
-}
-
 // CHECK-LABEL: sil @test_cond_fail
 // CHECK: bb0
 // CHECK-NEXT: tuple ()
@@ -62,19 +52,3 @@ bb0(%0 : $C):
   return %3 : $C
 }
 
-protocol Class : class {
-}
-
-class G : Class {
-}
-
-// CHECK-LABEL: sil @test_unconditional_checked_cast_class_exist
-// CHECK: unchecked_ref_cast
-// CHECK: return
-sil @test_unconditional_checked_cast_class_exist : $@convention(thin) (@owned Class) -> @owned G {
-bb0(%0 : $Class):
-  strong_retain %0 : $Class
-  %2 = unconditional_checked_cast %0 : $Class to G
-  strong_release %0 : $Class
-  return %2 : $G
-}
diff --git a/test/SILOptimizer/sil_combine_uncheck_ossa.sil b/test/SILOptimizer/sil_combine_uncheck_ossa.sil
@@ -15,16 +15,6 @@ class D : C {
 class E {
 }
 
-// CHECK-LABEL: sil [ossa] @test_unconditional_checked_cast
-// CHECK: bb0
-// CHECK-NEXT: unchecked_ref_cast
-// CHECK-NEXT: return
-sil [ossa] @test_unconditional_checked_cast : $@convention(thin) <T_0_0, T_0_1> (@owned RawBuffer) -> @owned HeapBufferStorage<T_0_0, T_0_1> {
-bb0(%0 : @owned $RawBuffer):
-  %3 = unconditional_checked_cast %0 : $RawBuffer to HeapBufferStorage<T_0_0, T_0_1>
-  return %3 : $HeapBufferStorage<T_0_0, T_0_1>
-}
-
 // CHECK-LABEL: sil [ossa] @test_cond_fail
 // CHECK: bb0
 // CHECK-NEXT: tuple ()
@@ -60,19 +50,3 @@ bb0(%0 : @owned $C):
   return %3 : $C
 }
 
-protocol Class : class {
-}
-
-class G : Class {
-}
-
-// CHECK-LABEL: sil [ossa] @test_unconditional_checked_cast_class_exist
-// CHECK: unchecked_ref_cast
-// CHECK: return
-sil [ossa] @test_unconditional_checked_cast_class_exist : $@convention(thin) (@owned Class) -> @owned G {
-bb0(%0 : @owned $Class):
-  %0a = copy_value %0 : $Class
-  %2 = unconditional_checked_cast %0a : $Class to G
-  destroy_value %0 : $Class
-  return %2 : $G
-}
diff --git a/test/SILOptimizer/simplify_unconditional_check_cast.sil b/test/SILOptimizer/simplify_unconditional_check_cast.sil
@@ -0,0 +1,54 @@
+// RUN: %target-sil-opt -enable-sil-verify-all %s -simplification -simplify-instruction=unconditional_checked_cast | %FileCheck %s
+
+import Swift
+import Builtin
+
+protocol P {}
+protocol PC: AnyObject {}
+
+struct S : P {}
+
+struct T {}
+
+class C {}
+
+// CHECK-LABEL: sil [ossa] @test_conforming_struct :
+// CHECK:         %1 = init_existential_metatype %0, $@thick any P.Type
+// CHECK-NEXT:    return %1
+// CHECK:       } // end sil function 'test_conforming_struct'
+sil [ossa] @test_conforming_struct : $@convention(thin) (@thick S.Type) -> @thick any P.Type {
+bb0(%0 : $@thick S.Type):
+  %1 = unconditional_checked_cast %0 to any P.Type
+  return %1
+}
+
+// CHECK-LABEL: sil [ossa] @test_non_conforming_struct :
+// CHECK:         %1 = unconditional_checked_cast %0
+// CHECK-NEXT:    return %1
+// CHECK:       } // end sil function 'test_non_conforming_struct'
+sil [ossa] @test_non_conforming_struct : $@convention(thin) (@thick T.Type) -> @thick any P.Type {
+bb0(%0 : $@thick T.Type):
+  %1 = unconditional_checked_cast %0 to any P.Type
+  return %1
+}
+
+
+// CHECK-LABEL: sil [ossa] @test_non_metatype :
+// CHECK:         %1 = unconditional_checked_cast %0
+// CHECK-NEXT:    return %1
+// CHECK:       } // end sil function 'test_non_metatype'
+sil [ossa] @test_non_metatype : $@convention(thin) (@guaranteed C) -> any PC {
+bb0(%0 : @guaranteed $C):
+  %1 = unconditional_checked_cast %0 to any PC
+  return %1
+}
+
+// CHECK-LABEL: sil [ossa] @test_non_existential_target :
+// CHECK:         %1 = unconditional_checked_cast %0
+// CHECK-NEXT:    return %1
+// CHECK:       } // end sil function 'test_non_existential_target'
+sil [ossa] @test_non_existential_target : $@convention(thin) (@thick S.Type) -> @thick Int.Type {
+bb0(%0 : $@thick S.Type):
+  %1 = unconditional_checked_cast %0 to Int.Type
+  return %1
+}
