Exploit this-return of a callsite in a this-return function.

For constructors/desctructors that return 'this', if there exists a callsite
that returns 'this' and is immediately before the return instruction, make
sure we are using the return value from the callsite.

We don't need to keep 'this' alive through the callsite. It also enables
optimizations in the backend, such as tail call optimization.

Updated from r177211.
rdar://12818789


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177541 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 64 insertions, 4 deletions

diff --git a/test/CodeGenCXX/arm.cpp b/test/CodeGenCXX/arm.cpp
index 3d3b147aa1..48f2f00840 100644
--- a/test/CodeGenCXX/arm.cpp
+++ b/test/CodeGenCXX/arm.cpp
@@ -56,15 +56,15 @@ namespace test1 {
   // CHECK:   [[THIS:%.*]] = alloca [[A]]*, align 4
   // CHECK:   store [[A]]* {{.*}}, [[A]]** [[THIS]]
   // CHECK:   [[THIS1:%.*]] = load [[A]]** [[THIS]]
-  // CHECK:   call [[A]]* @_ZN5test11AC2Ei(
-  // CHECK:   ret [[A]]* [[THIS1]]
+  // CHECK:   [[THIS2:%.*]] = call [[A]]* @_ZN5test11AC2Ei(
+  // CHECK:   ret [[A]]* [[THIS2]]
 
   // CHECK: define linkonce_odr [[A]]* @_ZN5test11AD1Ev([[A]]* %this) unnamed_addr
   // CHECK:   [[THIS:%.*]] = alloca [[A]]*, align 4
   // CHECK:   store [[A]]* {{.*}}, [[A]]** [[THIS]]
   // CHECK:   [[THIS1:%.*]] = load [[A]]** [[THIS]]
-  // CHECK:   call [[A]]* @_ZN5test11AD2Ev(
-  // CHECK:   ret [[A]]* [[THIS1]]
+  // CHECK:   [[THIS2:%.*]] = call [[A]]* @_ZN5test11AD2Ev(
+  // CHECK:   ret [[A]]* [[THIS2]]
 }
 
 // Awkward virtual cases.
diff --git a/test/CodeGenCXX/constructor-destructor-return-this.cpp b/test/CodeGenCXX/constructor-destructor-return-this.cpp
new file mode 100644
index 0000000000..1ff922de60
--- /dev/null
+++ b/test/CodeGenCXX/constructor-destructor-return-this.cpp
@@ -0,0 +1,60 @@
+//RUN: %clang_cc1 %s -emit-llvm -o - -triple=thumbv7-apple-ios3.0 -target-abi apcs-gnu | FileCheck %s
+
+// For constructors/desctructors that return 'this', if there exists a callsite
+// that returns 'this' and is immediately before the return instruction, make
+// sure we are using the return value from the callsite.
+// rdar://12818789
+
+// CHECK: define linkonce_odr [[A:%.*]] @_ZN11ObjectCacheC1Ev([[A]] %this) unnamed_addr
+// CHECK: [[THIS1:%.*]] = call [[A]] @_ZN11ObjectCacheC2Ev(
+// CHECK-NEXT: ret [[A]] [[THIS1]]
+
+// CHECK: define linkonce_odr [[A:%.*]] @_ZN5TimerI11ObjectCacheEC1EPS0_MS0_FvPS1_E([[A]] %this
+// CHECK: [[THIS1:%.*]] = call [[A]] @_ZN5TimerI11ObjectCacheEC2EPS0_MS0_FvPS1_E(
+// CHECK-NEXT: ret [[A]] [[THIS1]]
+
+// CHECK: define linkonce_odr [[A:%.*]] @_ZN5TimerI11ObjectCacheED1Ev([[A]] %this) unnamed_addr
+// CHECK: [[THIS1:%.*]] = call [[A]] @_ZN5TimerI11ObjectCacheED2Ev(
+// CHECK-NEXT: ret [[A]] [[THIS1]]
+
+// CHECK: define linkonce_odr [[A:%.*]] @_ZN5TimerI11ObjectCacheED2Ev([[A]] %this) unnamed_addr
+// CHECK: [[THIS1:%.*]] = call [[B:%.*]] @_ZN9TimerBaseD2Ev(
+// CHECK-NEXT: [[THIS2:%.*]] = bitcast [[B]] [[THIS1]] to [[A]]
+// CHECK-NEXT: ret [[A]] [[THIS2]]
+
+class TimerBase {
+public:
+    TimerBase();
+    virtual ~TimerBase();
+};
+
+template <typename TimerFiredClass> class Timer : public TimerBase {
+public:
+    typedef void (TimerFiredClass::*TimerFiredFunction)(Timer*);
+
+    Timer(TimerFiredClass* o, TimerFiredFunction f)
+        : m_object(o), m_function(f) { }
+
+private:
+    virtual void fired() { (m_object->*m_function)(this); }
+
+    TimerFiredClass* m_object;
+    TimerFiredFunction m_function;
+};
+
+class ObjectCache {
+public:
+    explicit ObjectCache();
+    ~ObjectCache();
+
+private:
+    Timer<ObjectCache> m_notificationPostTimer;
+};
+
+inline ObjectCache::ObjectCache() : m_notificationPostTimer(this, 0) { }
+inline ObjectCache::~ObjectCache() { }
+
+ObjectCache *test() {
+  ObjectCache *dd = new ObjectCache();
+  return dd;
+}