[CodeGen] partially revert 2b4fa5348ee157b6b1a1af44d0137ca8c7a71573 to fix Objective-C static variable initialization

[arphaman]

Summary

The following commit:

commit 2b4fa5348ee157b6b1a1af44d0137ca8c7a71573
Author: Richard Smith <[e-mail]>
Date:   Sun Sep 29 05:08:46 2019 +0000

    For P0784R7: compute whether a variable has constant destruction if it
    has a constexpr destructor.

started emitting static variables in Objective-C with C++ acquire/release checks. This is not supported for Objective-C. I can't revert the commit right now, so this is a partial revert of the change, to make sure next week's release branch isn't broken.

[rjmccall]

clang/lib/CodeGen/CGDecl.cpp

377

The long-term fix here is probably for needsDestruction to say that variables of static storage duration of non-trivial ARC type and/or non-trivial C struct type don't need destruction.

[arphaman]

clang/lib/CodeGen/CGDecl.cpp

377

I don't have time to fix it properly right now, but I filed https://github.com/llvm/llvm-project/issues/93 to keep track of the issue. Can this be committed now before the branch next week to avoid shipping this bug in the release?

[rsmith]

clang/lib/CodeGen/CGDecl.cpp

377

A correct fix looks to be pretty trivial and this patch appears to break C++20 semantics, so let's fix it properly.

[rjmccall]

clang/lib/CodeGen/CGDecl.cpp

377

I agree.

[rsmith]

clang/lib/CodeGen/CGDecl.cpp

377

Done in llvmorg-10-init-17084-g7a38468e34e. Thanks for the report and the testcase :)

clang/lib/CodeGen/CGDecl.cpp

if (GD.getDecl()) {
     // Disable emission of the parent function for the OpenMP device codegen.
     CGOpenMPRuntime::DisableAutoDeclareTargetRAII NoDeclTarget(*this);
     (void)GetAddrOfGlobal(GD);
   }
 
   return Addr;
 }
 
+/// hasNontrivialDestruction - Determine whether a type's destruction is
+/// non-trivial. If so, and the variable uses static initialization, we must
+/// register its destructor to run on exit.
+static bool hasNontrivialDestruction(QualType T) {
+  CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+  return RD && !RD->hasTrivialDestructor();
+}
+
 /// AddInitializerToStaticVarDecl - Add the initializer for 'D' to the
 /// global variable that has already been created for it.  If the initializer
 /// has a different type than GV does, this may free GV and return a different
 /// one.  Otherwise it just returns GV.
 llvm::GlobalVariable *
 CodeGenFunction::AddInitializerToStaticVarDecl(const VarDecl &D,
                                                llvm::GlobalVariable *GV) {
   ConstantEmitter emitter(*this);
if (GV->getType()->getElementType() != Init->getType()) {
     OldGV->eraseFromParent();
   }
 
   GV->setConstant(CGM.isTypeConstant(D.getType(), true));
   GV->setInitializer(Init);
 
   emitter.finalize(GV);
 
-  if (D.needsDestruction(getContext()) && HaveInsertPoint()) {
+  if (hasNontrivialDestruction(D.getType()) && HaveInsertPoint()) {
     // We have a constant initializer, but a nontrivial destructor. We still
     // need to perform a guarded "initialization" in order to register the
     // destructor.
     EmitCXXGuardedInit(D, GV, /*PerformInit*/false);
   }
 
   return GV;
 }

clang/test/CodeGenCXX/const-init-cxx2a.cpp

-// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s -std=c++2a | FileCheck %s --implicit-check-not=cxx_global_var_init --implicit-check-not=cxa_atexit
-
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-pch -o %t.pch %s -std=c++2a
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -include-pch %t.pch -x c++ /dev/null -emit-llvm -o - -std=c++2a | FileCheck %s --implicit-check-not=cxx_global_var_init --implicit-check-not=cxa_atexit
+// RUN: %clang_cc1 -verify -triple x86_64-apple-darwin -emit-llvm -o - %s -std=c++2a | FileCheck %s
+// expected-no-diagnostics
 
 // CHECK: @a = global i32 123,
 int a = (delete new int, 123);
-
-struct B {
-  constexpr B() {}
-  constexpr ~B() { n *= 5; }
-  int n = 123;
-};
-// CHECK: @b = global {{.*}} i32 123
-extern constexpr B b = B();
-
-// CHECK: @_ZL1c = internal global {{.*}} i32 123
-const B c;
-int use_c() { return c.n; }
-
-struct D {
-  int n;
-  constexpr ~D() {}
-};
-D d;
-// CHECK: @d = global {{.*}} zeroinitializer
-
-D d_arr[3];
-// CHECK: @d_arr = global {{.*}} zeroinitializer
-
-thread_local D d_tl;
-// CHECK: @d_tl = thread_local global {{.*}} zeroinitializer
-
-// CHECK-NOT: @llvm.global_ctors
-
-// CHECK-LABEL: define {{.*}} @_Z1fv(
-void f() {
-  // CHECK-NOT: call
-  // CHECK: call {{.*}}memcpy
-  // CHECK-NOT: call
-  // CHECK: call {{.*}}memset
-  // CHECK-NOT: call
-  // CHECK: }
-  constexpr B b;
-  D d = D();
-}
-
-// CHECK-LABEL: define {{.*}} @_Z1gv(
-void g() {
-  // CHECK-NOT: call
-  // CHECK-NOT: cxa_guard
-  // CHECK-NOT: _ZGV
-  // CHECK: }
-  static constexpr B b1;
-  static const B b2;
-  static D d;
-  thread_local D d_tl;
-}

clang/test/CodeGenObjC/initialize-function-static.m

+// RUN: %clang_cc1 -triple x86_64-apple-macos10.15 -emit-llvm -fobjc-arc -o - %s | FileCheck %s
+
+@interface I
+@end
+
+I *i() {
+  static I *i = ((void *)0);
+  return i;
+}
+
+// CHECK-NOT: __cxa_guard_acquire
+// CHECK-NOT: __cxa_guard_release