Devirtualizer: fix a crash due to a not supported bitcast of ABI compatible types

include/swift/SILOptimizer/Utils/InstOptUtils.h

@@ -198,6 +198,20 @@ castValueToABICompatibleType(SILBuilder *builder, SILPassManager *pm,
                              SILLocation Loc,
                              SILValue value, SILType srcTy, SILType destTy,
                              ArrayRef<SILInstruction *> usePoints);
+
+/// Returns true if the layout of a generic nominal type is dependent on its generic parameters.
+/// This is usually the case. Some examples, where they layout is _not_ dependent:
+/// ```
+///    struct S<T> {
+///      var x: Int // no members which depend on T
+///    }
+///
+///    struct S<T> {
+///      var c: SomeClass<T> // a class reference does not depend on the layout of the class
+///    }
+/// ```
+bool layoutIsTypeDependent(NominalTypeDecl *decl);
+
 /// Peek through trivial Enum initialization, typically for pointless
 /// Optionals.
 ///

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/SILOptimizer/Utils/InstOptUtils.h"
+#include "swift/AST/CanTypeVisitor.h"
 #include "swift/AST/GenericSignature.h"
 #include "swift/AST/SemanticAttrs.h"
 #include "swift/AST/SubstitutionMap.h"
@@ -745,12 +746,133 @@ swift::castValueToABICompatibleType(SILBuilder *builder, SILPassManager *pm,
               false};
     }
   }
+  NominalTypeDecl *srcNominal = srcTy.getNominalOrBoundGenericNominal();
+  NominalTypeDecl *destNominal = destTy.getNominalOrBoundGenericNominal();
+  if (srcNominal && srcNominal == destNominal &&
+      !layoutIsTypeDependent(srcNominal) &&
+      srcTy.isObject() && destTy.isObject()) {
+
+    // This can be a result from whole-module reasoning of protocol conformances.
+    // If a protocol only has a single conformance where the associated type (`ID`) is some
+    // concrete type (e.g. `Int`), then the devirtualizer knows that `p.get()`
+    // can only return an `Int`:
+    // ```
+    //   public struct X2<ID> {
+    //     let p: any P2<ID>
+    //     public func testit(i: ID, x: ID) -> S2<ID> {
+    //       return p.get(x: x)
+    //     }
+    //   }
+    // ```
+    // and after devirtualizing the `get` function, its result must be cast from `Int` to `ID`.
+    //
+    // The `layoutIsTypeDependent` utility is basically only used here to assert that this
+    // cast can only happen between layout compatible types.
+    return {builder->createUncheckedForwardingCast(loc, value, destTy), false};
+  }
 
   llvm::errs() << "Source type: " << srcTy << "\n";
   llvm::errs() << "Destination type: " << destTy << "\n";
   llvm_unreachable("Unknown combination of types for casting");
 }
 
+namespace {
+  class TypeDependentVisitor : public CanTypeVisitor<TypeDependentVisitor, bool> {
+  public:
+    // If the type isn't actually dependent, we're okay.
+    bool visit(CanType type) {
+      if (!type->hasArchetype() && !type->hasTypeParameter())
+        return false;
+      return CanTypeVisitor::visit(type);
+    }
+
+    bool visitStructType(CanStructType type) {
+      return visitStructDecl(type->getDecl());
+    }
+    bool visitBoundGenericStructType(CanBoundGenericStructType type) {
+      return visitStructDecl(type->getDecl());
+    }
+    bool visitStructDecl(StructDecl *decl) {
+      auto rawLayout = decl->getAttrs().getAttribute<RawLayoutAttr>();
+      if (rawLayout) {
+        if (auto likeType = rawLayout->getResolvedScalarLikeType(decl)) {
+          return visit((*likeType)->getCanonicalType());
+        } else if (auto likeArray = rawLayout->getResolvedArrayLikeTypeAndCount(decl)) {
+          return visit(likeArray->first->getCanonicalType());
+        }
+      }
+
+      for (auto field : decl->getStoredProperties()) {
+        if (visit(field->getInterfaceType()->getCanonicalType()))
+          return true;
+      }
+      return false;
+    }
+
+    bool visitEnumType(CanEnumType type) {
+      return visitEnumDecl(type->getDecl());
+    }
+    bool visitBoundGenericEnumType(CanBoundGenericEnumType type) {
+      return visitEnumDecl(type->getDecl());
+    }
+    bool visitEnumDecl(EnumDecl *decl) {
+      if (decl->isIndirect())
+        return false;
+
+      for (auto elt : decl->getAllElements()) {
+        if (!elt->hasAssociatedValues() || elt->isIndirect())
+          continue;
+
+        if (visit(elt->getArgumentInterfaceType()->getCanonicalType()))
+          return true;
+      }
+      return false;
+    }
+
+    bool visitTupleType(CanTupleType type) {
+      for (auto eltTy : type.getElementTypes()) {
+        if (visit(eltTy->getCanonicalType()))
+          return true;
+      }
+      return false;
+    }
+
+    // A class reference does not depend on the layout of the class.
+    bool visitClassType(CanClassType type) {
+      return false;
+     }
+    bool visitBoundGenericClassType(CanBoundGenericClassType type) {
+      return false;
+    }
+
+    // The same for non-strong references.
+    bool visitReferenceStorageType(CanReferenceStorageType type) {
+      return false;
+    }
+
+    // All function types have the same layout.
+    bool visitAnyFunctionType(CanAnyFunctionType type) {
+      return false;
+    }
+
+    // The safe default for types we didn't handle above.
+    bool visitType(CanType type) {
+      return true;
+    }
+  };
+} // end anonymous namespace
+
+bool swift::layoutIsTypeDependent(NominalTypeDecl *decl) {
+  if (auto *classDecl = dyn_cast<ClassDecl>(decl)) {
+    return false;
+  } else if (auto *structDecl = dyn_cast<StructDecl>(decl)) {
+    return TypeDependentVisitor().visitStructDecl(structDecl);
+  } else {
+    auto *enumDecl = cast<EnumDecl>(decl);
+    return TypeDependentVisitor().visitEnumDecl(enumDecl);
+  }
+}
+
 ProjectBoxInst *swift::getOrCreateProjectBox(AllocBoxInst *abi,
                                              unsigned index) {
   SILBasicBlock::iterator iter(abi);

test/SILOptimizer/devirtualize_existential.swift

@@ -1,19 +1,187 @@
-// RUN: %target-swift-frontend %s -O -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend %s -O -Xllvm -sil-disable-pass=FunctionSignatureOpts -module-name=test -emit-sil | %FileCheck %s
+
+// RUN: %empty-directory(%t) 
+// RUN: %target-build-swift -wmo -O -Xllvm -sil-disable-pass=FunctionSignatureOpts -module-name=test %s -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s -check-prefix=CHECK-OUTPUT
+// REQUIRES: executable_test
+
+// Test conversions of return types.
+
+public struct S1<ID> {
+  var x: Int
+}
+
+protocol P1<ID> {
+  associatedtype ID
+
+  func get(x: ID) -> S1<ID>
+}
+
+struct Y1: P1 {
+  func get(x: Int) -> S1<Int> {
+    return S1(x: 27)
+  }
+}
+
+public struct X1<ID> {
+  let p: any P1<ID>
+
+  // CHECK-LABEL: sil {{.*}} @$s4test2X1V6testit1i1xAA2S1VyxGx_xtF :
+  // CHECK:         unchecked_trivial_bit_cast
+  // CHECK:       } // end sil function '$s4test2X1V6testit1i1xAA2S1VyxGx_xtF'
+  @_semantics("optimize.sil.specialize.generic.never")
+  @inline(never)
+  public func testit(i: ID, x: ID) -> S1<ID> {
+    return p.get(x: x)
+  }
+}
+
+public struct S2<ID> {
+  var x: String
+}
+
+protocol P2<ID> {
+  associatedtype ID
+
+  func get(x: ID) -> S2<ID>
+}
+
+struct Y2: P2 {
+  func get(x: Int) -> S2<Int> {
+    return S2(x: "27")
+  }
+}
+
+public struct X2<ID> {
+  let p: any P2<ID>
+
+  // CHECK-LABEL: sil {{.*}} @$s4test2X2V6testit1i1xAA2S2VyxGx_xtF :
+  // CHECK:         unchecked_bitwise_cast
+  // CHECK:       } // end sil function '$s4test2X2V6testit1i1xAA2S2VyxGx_xtF'
+  @_semantics("optimize.sil.specialize.generic.never")
+  @inline(never)
+  public func testit(i: ID, x: ID) -> S2<ID> {
+    return p.get(x: x)
+  }
+}
+
+
+class C3<T> {}
+
+public struct S3<ID> {
+  var x: C3<ID>
+}
+
+protocol P3<ID> {
+  associatedtype ID
+
+  func get(x: ID) -> S3<ID>
+}
+
+struct Y3: P3 {
+  func get(x: Int) -> S3<Int> {
+    return S3(x: C3<Int>())
+  }
+}
+
+public struct X3<ID> {
+  let p: any P3<ID>
+
+  // CHECK-LABEL: sil {{.*}} @$s4test2X3V6testit1i1xAA2S3VyxGx_xtF :
+  // CHECK:         unchecked_bitwise_cast
+  // CHECK:       } // end sil function '$s4test2X3V6testit1i1xAA2S3VyxGx_xtF'
+  @_semantics("optimize.sil.specialize.generic.never")
+  @inline(never)
+  public func testit(i: ID, x: ID) -> S3<ID> {
+    return p.get(x: x)
+  }
+}
+
+
+public class C4<T> {}
+
+protocol P4<ID> {
+  associatedtype ID
+
+  func get(x: ID) -> C4<ID>
+}
+
+struct Y4: P4 {
+  func get(x: Int) -> C4<Int> {
+    return C4()
+  }
+}
+
+public struct X4<ID> {
+  let p: any P4<ID>
+
+  // CHECK-LABEL: sil {{.*}} @$s4test2X4V6testit1i1xAA2C4CyxGx_xtF :
+  // CHECK:         unchecked_ref_cast
+  // CHECK:       } // end sil function '$s4test2X4V6testit1i1xAA2C4CyxGx_xtF'
+  @_semantics("optimize.sil.specialize.generic.never")
+  @inline(never)
+  public func testit(i: ID, x: ID) -> C4<ID> {
+    return p.get(x: x)
+  }
+}
+
+
+public struct S5<ID> {
+  var x: (Int, C4<ID>)
+}
+
+protocol P5<ID> {
+  associatedtype ID
+
+  func get(x: ID) -> S5<ID>
+}
+
+struct Y5: P5 {
+  func get(x: Int) -> S5<Int> {
+    return S5(x: (27, C4<Int>()))
+  }
+}
+
+public struct X5<ID> {
+  let p: any P5<ID>
+
+  // CHECK-LABEL: sil {{.*}} @$s4test2X5V6testit1i1xAA2S5VyxGx_xtF :
+  // CHECK:         unchecked_bitwise_cast
+  // CHECK:       } // end sil function '$s4test2X5V6testit1i1xAA2S5VyxGx_xtF'
+  @_semantics("optimize.sil.specialize.generic.never")
+  @inline(never)
+  public func testit(i: ID, x: ID) -> S5<ID> {
+    return p.get(x: x)
+  }
+}
+
+// Basic test
 
 protocol Pingable {
  func ping(_ x : Int);
 }
 class Foo : Pingable {
-  func ping(_ x : Int) { var t : Int }
+  func ping(_ x : Int) { _ = 1 }
 }
 
 // Everything gets devirtualized, inlined, and promoted to the stack.
-//CHECK: @$s24devirtualize_existential17interesting_stuffyyF
-//CHECK-NOT: init_existential_addr
-//CHECK-NOT: apply
-//CHECK: return
+//CHECK-LABEL: sil @$s4test17interesting_stuffyyF :
+//CHECK-NOT:     init_existential_addr
+//CHECK-NOT:     apply
+//CHECK:       } // end sil function '$s4test17interesting_stuffyyF'
 public func interesting_stuff() {
- var x : Pingable = Foo()
+ let x : Pingable = Foo()
  x.ping(1)
 }
 
+// CHECK-OUTPUT: S1<Int>(x: 27)
+print(X1<Int>(p: Y1()).testit(i: 1, x: 2))
+// CHECK-OUTPUT: S2<Int>(x: "27")
+print(X2<Int>(p: Y2()).testit(i: 1, x: 2))
+// CHECK-OUTPUT: S3<Int>(x: test.C3<Swift.Int>)
+print(X3<Int>(p: Y3()).testit(i: 1, x: 2))
+// CHECK-OUTPUT: test.C4<Swift.Int>
+print(X4<Int>(p: Y4()).testit(i: 1, x: 2))
+// CHECK-OUTPUT: S5<Int>(x: (27, test.C4<Swift.Int>))
+print(X5<Int>(p: Y5()).testit(i: 1, x: 2))
+