[CodeGen][CXX]: Fix no_destroy CG bug under specific circumstances

Summary:

Class with no user-defined destructor that has an inherited member that has a
non-trivial destructor and a non-default constructor will attempt to emit a
destructor despite being marked as __attribute((no_destroy)) in which case it
would trigger an assertion due to an incorrect assumption. 

In addition this adds missing test coverage for IR generation for no_destroy.

(Note that here use of no_destroy is synonymous with its global flag 
counterpart `-fno-c++-static-destructors` being enabled)

Differential Revision: https://reviews.llvm.org/D54344



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@346628 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 51 insertions, 0 deletions

diff --git a/lib/CodeGen/CGDeclCXX.cpp b/lib/CodeGen/CGDeclCXX.cpp
index 4a025c2765..2884f13871 100644
--- a/lib/CodeGen/CGDeclCXX.cpp
+++ b/lib/CodeGen/CGDeclCXX.cpp
@@ -64,6 +64,15 @@ static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
 /// static storage duration.
 static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
                             ConstantAddress Addr) {
+  // Honor __attribute__((no_destroy)) and bail instead of attempting
+  // to emit a reference to a possibly nonexistent destructor, which
+  // in turn can cause a crash. This will result in a global constructor
+  // that isn't balanced out by a destructor call as intended by the
+  // attribute. This also checks for -fno-c++-static-destructors and
+  // bails even if the attribute is not present.
+  if (D.isNoDestroy(CGF.getContext()))
+    return;
+  
   CodeGenModule &CGM = CGF.CGM;
 
   // FIXME:  __attribute__((cleanup)) ?
diff --git a/test/CodeGenCXX/attr-no-destroy-d54344.cpp b/test/CodeGenCXX/attr-no-destroy-d54344.cpp
new file mode 100644
index 0000000000..2e004d6426
--- /dev/null
+++ b/test/CodeGenCXX/attr-no-destroy-d54344.cpp
@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR  %s -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu %s -o - | FileCheck %s --check-prefix=CHECK-ATTR
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR -fno-c++-static-destructors %s -o - | FileCheck %s --check-prefix=CHECK-FLAG
+
+// Regression test for D54344. Class with no user-defined destructor
+// that has an inherited member that has a non-trivial destructor
+// and a non-default constructor will attempt to emit a destructor
+// despite being marked as __attribute((no_destroy)) in which case
+// it would trigger an assertion due to an incorrect assumption.
+
+// This test is more reliable with asserts to work as without 
+// the crash may (unlikely) could generate working but semantically
+// incorrect code.
+
+class a {
+public:
+  ~a();
+};
+class logger_base {
+  a d;
+};
+class e : logger_base {};
+#ifndef NOATTR
+__attribute((no_destroy))
+#endif
+e g;
+
+// In the absence of the attribute and flag, both ctor and dtor should
+// be emitted, check for that.
+// CHECK: @__cxx_global_var_init
+// CHECK: @__cxa_atexit
+
+// When attribute is enabled, the constructor should not be balanced
+// by a destructor. Make sure we have the ctor but not the dtor
+// registration.
+// CHECK-ATTR: @__cxx_global_var_init
+// CHECK-ATTR-NOT: @__cxa_atexit
+
+// Same scenario except with global flag (-fno-c++-static-destructors)
+// supressing it instead of the attribute. 
+// CHECK-FLAG: @__cxx_global_var_init
+// CHECK-FLAG-NOT: @__cxa_atexit