[Bug target/27827] [4.0/4.1 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

["dorit at il dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #43 from dorit at il dot ibm dot com  2006-08-07 20:35 -------
> I'm all for this.  info gcc says that w/o a guarantee of alignment, loops are
> duped, with an if selecting between vector and scalar loops, is this not
> accurate?  

yes

>I spent a day trying to get gcc to vectorize any of the generator's
> loops, and did not succeed (can you make it vectorize the provided benchmark
> code?).  

The aggressive unrolling in the provided example seems to be the first obstacle
to vectorize the code

> I also tried various unrollings of the inner loop, particularly no
> unrolling and unroll=2 (vector length).  I was unable to truly decipher the
> warning messages explaining the lack of vectorization, and I would truly
> welcome some help in fixing this.

I'd be happy to help decipher the vectorizer's dump file. please send the
un-unrolled version and the dump file generated by -fdump-tree-vect-details,
and I'll see if I can help.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827