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[Steve Langasek <steve.langasek@xxxxxxxxxxxxx>]

*** This bug is a duplicate of bug 1311866 ***
    https://bugs.launchpad.net/bugs/1311866

It appears that this bug is addressed by the SRU of gcc-4.8
4.8.4-2ubuntu1~14.04, currently in trusty-proposed awaiting completion
of verification, which updates to revision 222448 on the gcc-4.8 branch.
Marking this bug as a duplicate.

** This bug has been marked a duplicate of bug 1311866
   update binutils and GCC for trusty

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https://bugs.launchpad.net/bugs/1449117

Title:
  [Ubuntu 14.04] gcc 4.8: Improve vector performance by removing
  unnecessary swap optimizations

Status in gcc-4.8 package in Ubuntu:
  New

Bug description:
  For vector memory operations, GCC generates less efficient code for
  little endian POWER than for big endian POWER.  This is because the
  VSX vector loads and stores (lxvd2x, stxvd2x, lxvw4x, stxvw4x) assume
  a vector register element ordering where the lowest-numbered element
  resides in the most significant portion of the register.  That is,
  they operate according to a big-endian element ordering no matter what
  endian mode the machine is running in.  To generate correct code
  regardless of this, GCC will generate a lxvd2x/xxswapd pair of
  instructions for each load, and an xxswapd/stxvd2x pair of
  instructions for each store.  The extra xxswapd instructions force the
  vector elements into the proper lanes, but at a cost in performance.

  In August 2014, I added a pass to GCC that removes the extra swap
  operations when they are not necessary for correctness.  This greatly
  improves vector performance for ppc64el.  This optimization can be
  done for computations where all of the vector operations are "lane-
  insenstive"; that is, they don't care which lanes the computations are
  performed in, so long as values are stored back to memory in the
  correct order.

  To take advantage of this improved performance, I've backported the
  swap optimization pass to GCC 4.8 in revision r221713.  I would like
  to see this included in the next service release of 14.04 LTS.  I
  believe this is the only Ubuntu release using GCC 4.8.  A separate
  feature request has been opened for GCC 4.9.

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