RFA: Avoid versioning loop with unaligned step

[Joern Wolfgang Rennecke <gnu at amylaar dot uk>]

eSi-RISC has vector permute functionality, but no unaligned loads. We 
see execution failures on gcc.dg/vect/slp-perm-12.c because loop 
versioning is used to make the tptr aligned for the first loop 
iteration, and then with a step of originally 11, 22 after 
vectorization, and a vector alignment of 8 bytes, the second iteration 
causes an AlignmentError exception.
The attached patch to tree-vect-data-refs.c suppresses attempts to align 
data accesses where the
step alignment times the vectorization factor is insufficient to sustain 
the alignment during the loop.
Bootstrapped and regression tested on x86_64-pc-linux-gnu .

I have also attached a matching testsuite patch to not expect SLP 
vectorization for slp-perm-12 when
no unaligned loads are available, although in terms of testing, I can 
only say that it works for us.

Attachment: aligned-step-diff-r267262.txt
Description: Text document

Attachment: aligned-step-diff-testsuite.txt
Description: Text document