RFR (XXS): 8208672: Enable -Wreorder in make files

[Thomas Schatzl]

Hi David,

On Tue, 2018-08-07 at 07:17 +1000, David Holmes wrote:
> Hi Thomas,
> 
> On 6/08/2018 10:38 PM, Thomas Schatzl wrote:
> > Hi David,
> > 
> > On Fri, 2018-08-03 at 10:20 +1000, David Holmes wrote:
> > > Hi Thomas,
> > > 
> > > On 2/08/2018 7:14 PM, Thomas Schatzl wrote:
> > > > Hi all,
> > > > 
> > > >     there have been several suggestions to try to fix the
> > > > Hotspot code to allow us to enable -Wreorder in the Hotspot
> > > > sources.
> > > > This should make problems due to use-before-initialization much
> > > > more obvious.
> > > > 
> > > > This change enables -Wreorder for gcc and clang.
> > > 
> > > For Windows (VS2017+) see:
> > > 
> > > https://docs.microsoft.com/en-us/cpp/error-messages/compiler-
> > > warnings /c5038
> > > 
> > > Otherwise change seems okay.
> > > 
> > 
> > Thanks!
> > 
> > http://cr.openjdk.java.net/~tschatzl/8208672/webrev.0_to_1 (diff)
> > http://cr.openjdk.java.net/~tschatzl/8208672/webrev.1 (full)
> > 
> > I verified that all our platforms (including Windows) still build.
> 
> I think the Windows change needs to be based on the compiler version 
> used as, from what I read, the flag only exists in VS2017.

  jdk11 official compiler is VS2017 so I figured it would not be that
much of a problem.
Another reason for my thinking is that MSVC 2013 does not implement
some interesting C++11 features anyway so we might be forced to drop
support for it soon (and the situation is of course worse if we upgrade
to C++14).

I looked a bit at the makefile and conditionalizing this on VS2017 (or
checking only whether VS2013 let it slide, i.e. give an "unsupported
option" warning but continue anyway because I would need to setup a
Windows dev environment somewhere) would take me a lot of time. 

Would it be possible to skip -Werror support for Visual Studio now and
try to fix this in a later enhancement? 

Thanks,
  Thomas