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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/57107] [4.9 Regression] tree check fail in unlink_stmt_vdef
Date: Tue, 30 Apr 2013 10:53:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57107

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-30 10:53:21 UTC ---
(gdb) call debug_gimple_stmt (stmt)
# .MEM_159(ab) = VDEF <.MEM>
D.63506 ={v} {CLOBBER};

SSA form is not up-to-date.  It's a latent issue with sinking clobbers
during EH cleanup.  We have

<L6>:
  # .MEM_32(ab) = VDEF <.MEM_31(ab)>
  D.2688 ={v} {CLOBBER};
  resx 3

<L7>:
  # .MEM_61 = VDEF <.MEM_32(ab)>
  MEM[(struct new_allocator *)&D.2706] ={v} {CLOBBER};
  # .MEM_62 = VDEF <.MEM_61>
  D.2706 ={v} {CLOBBER};
  # .MEM_34 = VDEF <.MEM_62>
  D.2706 ={v} {CLOBBER};
  resx 2

<L8>:
  # .MEM_35 = VDEF <.MEM_34>
  t ={v} {CLOBBER};
  resx 1

and first sink D.2688 ={v} {CLOBBER}; into the successor (L7), dropping
virtual operands.  Then we continue sinking but call unlink_stmt_vdef
on the moved stmt which no longer has up-to-date SSA form and thus
we ICE.

As we only sink across forwarder edges we can trivially keep the original
virtual operands in place.

I have a patch.