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

[Kim Barrett]

> On May 17, 2020, at 5:34 PM, Liu, Xin <xxinliu at amazon.com> wrote:
> 
> Hi, Kim,
> 
> Thank you to review my patch. I have removed the friend class BlockBegin.  
> Here is the new revision:  http://cr.openjdk.java.net/~xliu/8245051/01/webrev/

Looks good.

> About --with-extra-cflags, I completely agree. However,  how to configure OpenJDK is not under control. There're so many linux distributions.

I’m not sure what you mean by that.  The given configure options simply aren’t valid.
And if some linux distribution is patching the OpenJDK to allow such a configuration,
that’ s their lookout.

> In addition, it might cause subtle bugs if the toolchain is not gcc. From my side, I'd like to get rid of undefine behaviors as many as we can.  

I agree that it’s desirable to eliminate unnecessary or unintentional UB.

> Yes, I still need a reviewer and a sponsor.

Looks like Paul Hohense has volunteered.