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[RFC] By default if-convert only basic blocks that will be vectorized (take 4)

On Tue, Oct 22, 2013 at 08:27:54PM +0400, Sergey Ostanevich wrote:
> still fails on 403 et al.

Ok, reproduced, unfortunately the pending stmt sequences already pretty much
assume that they will end up in a single combined basic block.  I went
through various alternatives (deferring update_ssa (TODO_update_ssa) call
until after combine_blocks - doesn't work, because it is unhappy about
basic blocks being removed, temporarily putting all the stmts into latch
(doesn't work, because there are no PHIs for it in the loop), so the final
fix as discussed with Richard on IRC is not to predicate_bbs early before
versioning (unless -ftree-loop-if-convert-stores it is easily achievable
by just using a better dominance check for that), or for the stores stuff
doing it and freeing again (at least for now).

The predicate_bbs stuff would certainly appreciate more TLC in the future.

Attaching whole new patchset, the above mentioned fix is mostly in the
first patch (which also contains a tree-cfg.h include that is needed for
today's header reshufling), the other two patches are just tweaked to
apply on top of that.  All 3 patches together have been
bootstrapped/regtested on x86_64-linux and i686-linux, the first one
and first+second just compile time tested.


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