From 131aedee144b75feba1d620541fe39054acce7aa Mon Sep 17 00:00:00 2001
From: Erik Eckstein <eeckstein@apple.com>
Date: Mon, 20 Apr 2020 12:12:44 +0200
Subject: [PATCH] Devirtualizer: fix a miscompile due to handling of cast
 instructions.

getInstanceWithExactDynamicType returns a new instance and for this the class decl has to be updated.

https://bugs.swift.org/browse/SR-12538
rdar://problem/61911112
---
 lib/SILOptimizer/Utils/Devirtualize.cpp       | 18 +++++++--
 .../devirtualize_class_method.swift           | 37 +++++++++++++++++++
 2 files changed, 51 insertions(+), 4 deletions(-)
 create mode 100644 test/SILOptimizer/devirtualize_class_method.swift

diff --git a/lib/SILOptimizer/Utils/Devirtualize.cpp b/lib/SILOptimizer/Utils/Devirtualize.cpp
index 32d5c20e1fd52..cb5226de09012 100644
--- a/lib/SILOptimizer/Utils/Devirtualize.cpp
+++ b/lib/SILOptimizer/Utils/Devirtualize.cpp
@@ -1147,8 +1147,15 @@ swift::tryDevirtualizeApply(ApplySite applySite, ClassHierarchyAnalysis *cha,
 
     // Try to check if the exact dynamic type of the instance is statically
     // known.
-    if (auto instance = getInstanceWithExactDynamicType(cmi->getOperand(), cha))
-      return tryDevirtualizeClassMethod(fas, instance, cd, ore);
+    if (auto instance = getInstanceWithExactDynamicType(cmi->getOperand(), cha)) {
+      // Update the classDecl, because we are stripping casts more aggressively
+      // in getInstanceWithExactDynamicType than in stripUpCasts.
+      CanType classType = getSelfInstanceType(instance->getType().getASTType());
+      // This should never be null - make the check just to be on the safe side.
+      if (ClassDecl *cd = classType.getClassOrBoundGenericClass())
+        return tryDevirtualizeClassMethod(fas, instance, cd, ore);
+      return {ApplySite(), false};
+    }
 
     if (auto exactTy = getExactDynamicType(cmi->getOperand(), cha)) {
       if (exactTy == cmi->getOperand()->getType())
@@ -1207,8 +1214,11 @@ bool swift::canDevirtualizeApply(FullApplySite applySite,
 
     // Try to check if the exact dynamic type of the instance is statically
     // known.
-    if (auto instance = getInstanceWithExactDynamicType(cmi->getOperand(), cha))
-      return canDevirtualizeClassMethod(applySite, cd);
+    if (auto instance = getInstanceWithExactDynamicType(cmi->getOperand(), cha)) {
+      CanType classType = getSelfInstanceType(instance->getType().getASTType());
+      ClassDecl *cd = classType.getClassOrBoundGenericClass();
+      return cd && canDevirtualizeClassMethod(applySite, cd);
+    }
 
     if (auto exactTy = getExactDynamicType(cmi->getOperand(), cha)) {
       if (exactTy == cmi->getOperand()->getType())
diff --git a/test/SILOptimizer/devirtualize_class_method.swift b/test/SILOptimizer/devirtualize_class_method.swift
new file mode 100644
index 0000000000000..97a819da0bc66
--- /dev/null
+++ b/test/SILOptimizer/devirtualize_class_method.swift
@@ -0,0 +1,37 @@
+// RUN: %empty-directory(%t) 
+// RUN: %target-build-swift -O -module-name=test %s -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+// REQUIRES: executable_test
+
+class Base {
+  required init() { }
+
+  class func instance() -> Base {
+    return self.init()
+  }
+}
+
+class Middle: Base {
+  override class func instance() -> Middle {
+    return self.init()
+  }
+}
+
+class Derived: Middle {
+  required init() {
+    super.init()
+    print("init Derived")
+  }
+}
+
+struct Maker<C: Base> {
+  @inline(never)
+  static func create() -> Base {
+    return C.instance()
+  }
+}
+
+// CHECK: init Derived
+// CHECK: test.Derived
+print(Maker<Derived>.create())
+