IRGen: fix failing unconditional class casts

When unconditionally casting from a base to a final derived class, e.g. `base as! Derived`, the program did not abort with a trap.
Instead the resulting null-pointer caused a crash later in the program.
This fix inserts a trap condition for the failing case of such a cast.

rdar://151462303

lib/IRGen/GenCast.cpp

@@ -1032,7 +1032,7 @@ void irgen::emitScalarCheckedCast(IRGenFunction &IGF,
   }
 
   if (llvm::Value *fastResult = emitFastClassCastIfPossible(
-          IGF, instance, sourceFormalType, targetFormalType,
+          IGF, instance, sourceFormalType, targetFormalType, mode,
           sourceWrappedInOptional, nilCheckBB, nilMergeBB)) {
     Explosion fastExplosion;
     fastExplosion.add(fastResult);
@@ -1054,7 +1054,7 @@ void irgen::emitScalarCheckedCast(IRGenFunction &IGF,
 /// not required that the metadata is fully initialized.
 llvm::Value *irgen::emitFastClassCastIfPossible(
     IRGenFunction &IGF, llvm::Value *instance, CanType sourceFormalType,
-    CanType targetFormalType, bool sourceWrappedInOptional,
+    CanType targetFormalType, CheckedCastMode mode, bool sourceWrappedInOptional,
     llvm::BasicBlock *&nilCheckBB, llvm::BasicBlock *&nilMergeBB) {
   if (!doesCastPreserveOwnershipForTypes(IGF.IGM.getSILModule(),
                                          sourceFormalType, targetFormalType)) {
@@ -1089,15 +1089,18 @@ llvm::Value *irgen::emitFastClassCastIfPossible(
 
   // If the source was originally wrapped in an Optional, check it for nil now.
   if (sourceWrappedInOptional) {
-    auto isNotNil = IGF.Builder.CreateICmpNE(
+    auto isNil = IGF.Builder.CreateICmpEQ(
         instance, llvm::ConstantPointerNull::get(
                       cast<llvm::PointerType>(instance->getType())));
-    auto *isNotNilContBB = llvm::BasicBlock::Create(IGF.IGM.getLLVMContext());
-    nilMergeBB = llvm::BasicBlock::Create(IGF.IGM.getLLVMContext());
-    nilCheckBB = IGF.Builder.GetInsertBlock();
-    IGF.Builder.CreateCondBr(isNotNil, isNotNilContBB, nilMergeBB);
-
-    IGF.Builder.emitBlock(isNotNilContBB);
+    if (mode == CheckedCastMode::Unconditional) {
+      IGF.emitConditionalTrap(isNil, "Unexpectedly found nil while unwrapping an Optional value");
+    } else {
+      auto *isNotNilContBB = llvm::BasicBlock::Create(IGF.IGM.getLLVMContext());
+      nilMergeBB = llvm::BasicBlock::Create(IGF.IGM.getLLVMContext());
+      nilCheckBB = IGF.Builder.GetInsertBlock();
+      IGF.Builder.CreateCondBr(isNil, nilMergeBB, isNotNilContBB);
+      IGF.Builder.emitBlock(isNotNilContBB);
+    }
   }
 
   // Get the metadata pointer of the destination class type.
@@ -1121,11 +1124,15 @@ llvm::Value *irgen::emitFastClassCastIfPossible(
   llvm::Value *rhs = IGF.Builder.CreateBitCast(objMetadata, IGF.IGM.Int8PtrTy);
   
   // return isa_ptr == metadata_ptr ? instance : nullptr
-  llvm::Value *isEqual = IGF.Builder.CreateCmp(llvm::CmpInst::Predicate::ICMP_EQ,
+  llvm::Value *isNotEqual = IGF.Builder.CreateCmp(llvm::CmpInst::Predicate::ICMP_NE,
                                               lhs, rhs);
+  if (mode == CheckedCastMode::Unconditional) {
+    IGF.emitConditionalTrap(isNotEqual, "Unconditional cast failed");
+    return instance;
+  }
   auto *instanceTy = cast<llvm::PointerType>(instance->getType());
   auto *nullPtr = llvm::ConstantPointerNull::get(instanceTy);
-  auto *select = IGF.Builder.CreateSelect(isEqual, instance, nullPtr);
+  auto *select = IGF.Builder.CreateSelect(isNotEqual, nullPtr, instance);
   llvm::Type *destTy = IGF.getTypeInfoForUnlowered(targetFormalType).getStorageType();
   return IGF.Builder.CreateBitCast(select, destTy);
 }

lib/IRGen/GenCast.h

@@ -61,7 +61,7 @@ namespace irgen {
 
   llvm::Value *emitFastClassCastIfPossible(
       IRGenFunction &IGF, llvm::Value *instance, CanType sourceFormalType,
-      CanType targetFormalType, bool sourceWrappedInOptional,
+      CanType targetFormalType, CheckedCastMode mode, bool sourceWrappedInOptional,
       llvm::BasicBlock *&nilCheckBB, llvm::BasicBlock *&nilMergeBB);
 
   /// Convert a class object to the given destination type,

test/Casting/CastTraps.swift.gyb

@@ -142,4 +142,35 @@ CastTrapsTestSuite.test("Unexpected Obj-C null")
 }
 #endif
 
+class Base {}
+final class Derived: Base {}
+final class Other: Base {}
+
+@inline(never)
+func getDerived(_ v: Base) -> Derived {
+  return v as! Derived
+}
+
+@inline(never)
+func getDerivedFromOptional(_ v: Base?) -> Derived {
+  return v as! Derived
+}
+
+CastTrapsTestSuite.test("unconditinal fast class cast") {
+  let c = Other()
+  expectCrashLater()
+  _ = getDerived(c)
+}
+
+CastTrapsTestSuite.test("unconditinal optional fast class cast") {
+  let c = Other()
+  expectCrashLater()
+  _ = getDerivedFromOptional(c)
+}
+
+CastTrapsTestSuite.test("unconditinal optional nil fast class cast") {
+  expectCrashLater()
+  _ = getDerivedFromOptional(nil)
+}
+
 runAllTests()

test/Casting/fast_class_casts.swift

@@ -56,6 +56,15 @@ func unconditionalCastToFinal(_ b: Classes.Base) -> Classes.Final {
   return b as! Classes.Final
 }
 
+// CHECK-LABEL: define {{.*}} @"$s4Main32unconditionalOptionalCastToFinaly7Classes0F0CAC4BaseCSgF"
+// CHECK-NOT:     call {{.*}}@object_getClass
+// CHECK-NOT:     @swift_dynamicCastClass
+// CHECK:       }
+@inline(never)
+func unconditionalOptionalCastToFinal(_ b: Classes.Base?) -> Classes.Final {
+  return b as! Classes.Final
+}
+
 // CHECK-LABEL: define {{.*}} @"$s4Main20castToResilientFinaly0D7Classes0E0CSgAC4BaseCF"
 // CHECK:         @swift_dynamicCastClass
 // CHECK:       }
@@ -132,7 +141,9 @@ func test() {
   // CHECK-OUTPUT: Optional(Classes.Final)
   print(castToFinal(Classes.Final()) as Any)
   // CHECK-OUTPUT: Classes.Final
-  print(unconditionalCastToFinal(Classes.Final()) as Any)
+  print(unconditionalCastToFinal(Classes.Final()))
+  // CHECK-OUTPUT: Classes.Final
+  print(unconditionalOptionalCastToFinal(Classes.Final()))
 
   // CHECK-OUTPUT: nil
   print(castToResilientFinal(ResilientClasses.Base()) as Any)

test/IRGen/casts.sil

@@ -1,6 +1,6 @@
 // RUN: %target-swift-frontend %s -emit-ir -enable-objc-interop -disable-objc-attr-requires-foundation-module | %FileCheck %s -DINT=i%target-ptrsize
 
-// REQUIRES: CPU=i386 || CPU=x86_64
+// REQUIRES: CPU=i386 || CPU=x86_64 || CPU=arm64
 
 sil_stage canonical
 
@@ -11,9 +11,11 @@ struct NotClass {}
 
 class A {}
 class B: A {}
+final class F: A {}
 
 sil_vtable A {}
 sil_vtable B {}
+sil_vtable F {}
 
 // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc ptr @unchecked_addr_cast(ptr noalias {{(nocapture|captures\(none\))}} dereferenceable({{.*}}) %0) {{.*}} {
 sil @unchecked_addr_cast : $(@in A) -> B {
@@ -115,6 +117,42 @@ entry(%a : $@thick Any.Type):
   return %p : $@thick (CP & OP & CP2).Type
 }
 
+// CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc ptr @unconditional_fast_class_cast(ptr %0)
+// CHECK:         [[ISA:%.*]] = load ptr, ptr %0
+// CHECK:         [[NE:%.*]] = icmp ne {{.*}}, [[ISA]]
+// CHECK:         [[E:%.*]] = call i1 @llvm.expect.i1(i1 [[NE]], i1 false) 
+// CHECK:         br i1 [[E]], label %[[TRAPBB:[0-9]*]], label %[[RETBB:[0-9]*]]
+// CHECK:       [[RETBB]]:
+// CHECK-NEXT:    ret ptr %0
+// CHECK:       [[TRAPBB]]:
+// CHECK-NEXT:    call void @llvm.trap()
+sil @unconditional_fast_class_cast : $@convention(thin) (@owned A) -> @owned F {
+entry(%0 : $A):
+  %1 = unconditional_checked_cast %0 to F
+  return %1
+}
+
+// CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc ptr @unconditional_optional_fast_class_cast(i64 %0)
+// CHECK:         [[PTR:%.*]] = inttoptr i64 %0 to ptr
+// CHECK:         [[ISNULL:%.*]] = icmp eq ptr [[PTR]], null
+// CHECK:         [[ENN:%.*]] = call i1 @llvm.expect.i1(i1 [[ISNULL]], i1 false) 
+// CHECK:         br i1 [[ENN]], label %[[NULLTRAPBB:[0-9]*]], label %[[CONTBB:[0-9]*]]
+// CHECK:       [[CONTBB]]:
+// CHECK:         [[ISA:%.*]] = load ptr, ptr [[PTR]]
+// CHECK:         [[NE:%.*]] = icmp ne {{.*}}, [[ISA]]
+// CHECK:         [[E:%.*]] = call i1 @llvm.expect.i1(i1 [[NE]], i1 false) 
+// CHECK:         br i1 [[E]], label %[[TRAPBB:[0-9]*]], label %[[RETBB:[0-9]*]]
+// CHECK:       [[RETBB]]:
+// CHECK-NEXT:    ret ptr [[PTR]]
+// CHECK:       [[NULLTRAPBB]]:
+// CHECK-NEXT:    call void @llvm.trap()
+// CHECK:       [[TRAPBB]]:
+// CHECK-NEXT:    call void @llvm.trap()
+sil @unconditional_optional_fast_class_cast : $@convention(thin) (@owned Optional<A>) -> @owned F {
+entry(%0 : $Optional<A>):
+  %1 = unconditional_checked_cast %0 to F
+  return %1
+}
 
 // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc { ptr, ptr } @c_cast_to_class_existential(ptr %0)
 // CHECK:         call { ptr, ptr } @dynamic_cast_existential_1_conditional(ptr {{.*}}, ptr %.Type, {{.*}} @"$s5casts2CPMp"