[PATCH PR92926]Fix wrong code caused by ctor node translation unit wide sharing

[bin.cheng]

Hi,

As reported in PR92926, constant ctor is shared translation unit wide because 
of constexpr_call_table,
however, during gimplify, the shared ctor could be modified.  This patch fixes 
the issue by unsharing
it before modification in gimplify.  A test is reduced from cppcoro library and 
added.

Bootstrap and test ongoing.  Not sure if this is the correct fix though, any 
comments?

Thanks,
bin

2019-12-13  Bin Cheng  <bin.li...@linux.alibaba.com>

        PR tree-optimization/92926
        * gimplify.c (gimplify_init_constructor): Unshare ctor node before
        clearing.

gcc/testsuite
2019-12-13  Bin Cheng  <bin.li...@linux.alibaba.com>

        PR tree-optimization/92926
        * g++.dg/pr92926.C: New test.

0001-pr92926.patch
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