[PR44181] skip debug insns when inserting IV updates

[Alexandre Oliva]

A number of graphite -fcompare-debug bug reports were fixed with this
patch.  The problem was that we inserted induction variable increment
stmts before the last stmt in the block, but if the block ended with a
fall-through, the insert would be before a non-debug stmt in the non-VTA
case, whereas in the VTA case it could be before a debug stmt, after the
non-debug stmt.  Skipping trailing debug stmts so that we insert before
the last non-debug stmt removed the codegen differences.

Bootstrapped the compiler, along with the upcoming patch for PR43656, on
x86_64-linux-gnu, with the following options:

-O2 -g -fschedule-insns -fsched-pressure -funroll-loops -fgraphite-identity

for stage2 and stage3 host, and for stage3 libs (also -fcompare-debug)

I got build failures on zlib and libada, presumably because of this
unusual combination of flags, but no -fcompare-debug errors.

Ok to install?

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-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist      Red Hat Brazil Compiler Engineer