RFR(XS): 8245051: c1 is broken if it is compiled by gcc without -fno-lifetime-dse

[Kim Barrett]

> On May 15, 2020, at 2:49 PM, Liu, Xin <xxinliu at amazon.com> wrote:
> 
> Hi, 
> 
> Please review the following patch. 
> Jbs: https://bugs.openjdk.java.net/browse/JDK-8245051
> Webrev: http://cr.openjdk.java.net/~xliu/8245051/00/webrev/
> 
> I found this problem from centos’s java-11-openjdk. https://git.centos.org/rpms/java-11-openjdk/blob/c7/f/SPECS/java-11-openjdk.spec#_1327
> '-std=gnu++98' is not a valid option for cc1. As a result, configure will fail to determine gcc supports -fno-lifetime-dse or not. 
> C1 acts weird if it is compiled by GCC without that flag. 
> 
> After then, I built hotspot with -fsanitize=undefined. I found some interesting points for c1.  With this patch, I can build the whole openjdk without -fno-lifetime-dse. 
> I've tested hotspot:tier1 and "gtest:all". Even though everything looks fine, I don't think we reach a point to lift "-fno-lifetime-dse".  This patch just attempts to fix C1. 
> 
> Thanks, 
> --lx

Thanks for finding these.

The change to c1_ValueMap.cpp looks good to me. 

The changes to c1_Instruction.hpp also look good to me.  In addition,
Instruction no longer needs to befriend BlockBegin.  Please make that
change before pushing.

However, I have to question the configure options being used. Some
(many? all?) of the options being passed in as --with-extra-cflags and
friends are already used properly by the build system, and don't need
to be added that way, and may even cause problems. That's what's
happening with -std=gnu++98, which is not a valid option for compling
C code, but the build system will use it when compiling C++ code.
That's been true since JDK 9 (JDK-8156980).

We definitely cannot remove -fno-lifetime-dse.  There are a number of
other places where we're doing weird things in allocators/deallocators
that are similarly bogus.  The ResourceObj allocation_type stuff is
just one example; I'm pretty sure there are others.

I'm running these changes (including the friendship removal) through
more extensive testing. I'll report back when done, but I don't expect
that to find anything.

It looks like you will need a sponsor? Hopefully a compiler person
will also review and sponsor.