[Bug c++/81237] New: Cannot link when class methods compiled with different levels of vectorization

["ravi dot kappiyoor at cd-adapco dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81237

            Bug ID: 81237
           Summary: Cannot link when class methods compiled with different
                    levels of vectorization
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ravi.kappiyoor@cd-adapco.com
  Target Milestone: ---

I have 4 files (2 CPP files, 1 header file, and 1 Makefile), shown below:

**test.h**
#ifndef test_h_
#define test_h_

#include <string>

class A
{
public:
  virtual ~A() {}
protected:
};
class B
{
public:
  virtual std::string const func() const = 0;
protected:
  B() {}
  virtual ~B() {}
};
class C : public A
        , public B
{
public:
  ~C();
private:
  std::string const func() const;
};

#endif

**test.cpp**
#include "test.h"

C::~C() {}

**test2.cpp**
#include "test.h"

std::string const
C::func() const
{
  return 0;
}

**Makefile**
all:
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu7.1.0/bin/g++ -O3
--param inline-unit-growth=1000 -fPIC -o test2.o -c test2.cpp
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu7.1.0/bin/g++ -fPIC -O3
--param inline-unit-growth=1000 -shared -z defs -Wl,--as-needed -shared
-Wl,-soname,libTest2.so -o libTest2.so test2.o
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu7.1.0/bin/g++ -O3
--param inline-unit-growth=1000 -fPIC -mavx512f -fabi-version=6 -o test.o -c
test.cpp
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu7.1.0/bin/g++ -fPIC -O3
--param inline-unit-growth=1000 -shared -z defs -Wl,--as-needed -shared
-Wl,-soname,libTest.so -o libTest.so test.o libTest2.so

old:
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu6.2.0/bin/g++ -O3
--param inline-unit-growth=1000 -fPIC -o test2.o -c test2.cpp
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu6.2.0/bin/g++ -fPIC -O3
--param inline-unit-growth=1000 -shared -z defs -Wl,--as-needed -shared
-Wl,-soname,libTest2.so -o libTest2.so test2.o
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu6.2.0/bin/g++ -O3
--param inline-unit-growth=1000 -fPIC -mavx512f -fabi-version=6 -o test.o -c
test.cpp
        ${MIRROR_HOME}/compilers/linux-x86_64-2.10.1/gnu6.2.0/bin/g++ -fPIC -O3
--param inline-unit-growth=1000 -shared -z defs -Wl,--as-needed -shared
-Wl,-soname,libTest.so -o libTest.so test.o libTest2.so

* **test2.cpp** is compiled with SSE2 instructions to create **libTest2.so**
* **test.cpp** is compiled with AVX-512 instructions (the flags "-mavx512f
-fabi-version=6" are added to it's compile)
* If both CPP files are instead compiled with the same vectorization level (via
the removal of the extra flags for **test.cpp** or the addition of the same
flags for **test2.cpp**), then the compile works as expected. 
* The linker appears to be getting confused when some of the methods in the
class are compiled with one vectorization level, while other methods are
compiled with another, causing the "undefined reference" error.
* As far as I am aware, it is not illegal via the standard to compile certain
methods of a class with one level of vectorization and not other methods - this
appears to be a compiler bug.
* When using "make old" (i.e., using GNU 6.2 instead of GNU 7.1), the compile
works as expected even when using different levels of vectorization.