Undefined references to static const members of class templates (but not when const is omitted)

[llvmbot]

Bugzilla Link	26006
Version	trunk
OS	Linux
Attachments	Test program to reproduce
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@zahiraam

Extended Description

The below program (also attached) produces an undefined reference to Foo::Bar<int>::m when m is declared as const. Just compile it with clang++ test.cpp. It does not compile with the latest clang from the trunk, nor with clang 3.5.

However, when m does not have any additional qualifiers or when m is declared as const volatile, then the program compiles, links, and runs. You can verify this by defining QUALS as empty or as const volatile.

GCC compiles and links the program fine.

This code was distilled from xulrunner 24.8.0.

#define QUALS	const
//#define QUALS	const volatile
//#define QUALS

class Foo {
public:
	template <typename T>
	struct Bar {
		static QUALS long m;
	};

	static QUALS long& getter() { return Bar<int>::m; }

	static int f();
};

template <typename T>
QUALS long Foo::Bar<T>::m = 1;

int Foo::f()
{
	return getter();
}

int main()
{
	return Foo::f();
}

[zahiraam]

Here is another test case with the same fail on Linux and Windows.
gcc and MSVC compile it.

#include <stdio.h>

template <class charT>
struct basic_string
{
  static const int npos;
  basic_string(int = npos) {;}
};

basic_string<char> s;

template <class charT>
const int
basic_string<charT>::npos = -1;



extern "C" { int puts(const char *); }

int main() {
  puts("Should compile without ACCVIOing");
}

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#38106

[AaronBallman]

https://gcc.godbolt.org/z/W19qMvq5x

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: None (llvmbot)

| | | | --- | --- | | Bugzilla Link | [26006](https://llvm.org/bz26006) | | Version | trunk | | OS | Linux | | Attachments | [Test program to reproduce](https://user-images.githubusercontent.com/60944935/143752720-1376f383-0701-4af6-8b5e-cb583850f1f6.gz) | | Reporter | LLVM Bugzilla Contributor | | CC | @DougGregor,@zahiraam |

Extended Description

The below program (also attached) produces an undefined reference to Foo::Bar<int>::m when m is declared as const. Just compile it with clang++ test.cpp. It does not compile with the latest clang from the trunk, nor with clang 3.5.

However, when m does not have any additional qualifiers or when m is declared as const volatile, then the program compiles, links, and runs. You can verify this by defining QUALS as empty or as const volatile.

GCC compiles and links the program fine.

This code was distilled from xulrunner 24.8.0.

#define QUALS	const
//#define QUALS	const volatile
//#define QUALS

class Foo {
public:
	template <typename T>
	struct Bar {
		static QUALS long m;
	};

	static QUALS long& getter() { return Bar<int>::m; }

	static int f();
};

template <typename T>
QUALS long Foo::Bar<T>::m = 1;

int Foo::f()
{
	return getter();
}

int main()
{
	return Foo::f();
}