[Bug tree-optimization/35642] heisenbug in tree vectorizer

["zadeck at naturalbridge dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from zadeck at naturalbridge dot com  2008-03-20 13:59 -------
Subject: Re:  heisenbug in tree vectorizer

bonzini at gnu dot org wrote:
> ------- Comment #7 from bonzini at gnu dot org  2008-03-20 13:51 -------
> Indeed my patch exposes additional vectorization abilities (which was
> unexpected).
>
> Kenny, can you run the failing testcase under valgrind?
>
>
>   
I did run it under valgrind and found no problems. 

However, i am a little skeptical about regression hunting for these 
failures.   I have found that they come and go based on small changes to 
other parts of the compiler, i.e. they are symptomatic of some 
uninitialized variable problem or a storage overwriting.  

in particular, with the release that i specified in message 1, the 
failures were there if the compiler was not bootstrapped and were there 
if it was bootstrapped.  Also, changes that i made to that release in 
the register allocator, which is far downstream of the tree vectorizer 
caused the problems to hit for both bootstrapped and not bootstrapped 
builds.   

I would suggest that you go roll back to that release mentioned in 
message 1, where you have exactly the same code base for bootstrapped 
and non bootstrapped compiler and run the two compilers in parallel 
until you find the place where they diverge.

It could very well be that this may be that this is a problem with 
someone elses code, but you are the occam's razor first choice.

kenny


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35642