[Bug tree-optimization/56294] BOOT_CFLAGS='-O2 -g -fno-ipa-sra' leads to bootstrap comparison failure

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56294

--- Comment #15 from Martin Jambor <jamborm at gcc dot gnu.org> 2013-03-04 17:15:25 UTC ---
(In reply to comment #13)
> A guess is that you end up creating SSA names during code transform in
> different
> order - which can result from walking a hashtable to do things (which might
> be in different order when it doesn't have the same number of entries).

I have verified in the debugger that SRA does not create any new SSA
names on its own, all of them are created by renaming after the pass
finishes (i.e. by TODO_update_ssa).

> Note that if you process debug stmts _at all_ (thus end up creating new SSA
> names because of them) then this will break as well.

I'm not sure what you mean.  SRA does not process debug stmts but it
now creates them.  The re-namer is apparently clever enough not to
create a PHI node and thus a new SSA name because of debug statements,
yet it manages to create them in a different order, probably because
it sees uses were there are none without debug statements.  Can that
be the case?  Is creating such uses really a bug?