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Message #91370
[Bug 1449119] Re: [Ubuntu 15.10] gcc: Optimize swap removal in presence of floating-point vector convert/splat sequence
fixed in gcc-4.8 in trusty-updates
fixed in all version in 15.10.
** Package changed: gcc-defaults (Ubuntu) => gcc-4.8 (Ubuntu)
** Also affects: gcc-4.9 (Ubuntu)
Importance: Undecided
Status: New
** Also affects: gcc-5 (Ubuntu)
Importance: Undecided
Status: New
** Also affects: gcc-4.8 (Ubuntu Trusty)
Importance: Undecided
Status: New
** Also affects: gcc-4.9 (Ubuntu Trusty)
Importance: Undecided
Status: New
** Also affects: gcc-5 (Ubuntu Trusty)
Importance: Undecided
Status: New
** No longer affects: gcc-4.9 (Ubuntu Trusty)
** No longer affects: gcc-5 (Ubuntu Trusty)
** Changed in: gcc-4.8 (Ubuntu Trusty)
Status: New => Fix Released
** Changed in: gcc-4.8 (Ubuntu)
Status: In Progress => Fix Released
** Changed in: gcc-4.9 (Ubuntu)
Status: New => Fix Released
** Changed in: gcc-5 (Ubuntu)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/1449119
Title:
[Ubuntu 15.10] gcc: Optimize swap removal in presence of floating-
point vector convert/splat sequence
Status in gcc-4.8 package in Ubuntu:
Fix Released
Status in gcc-4.9 package in Ubuntu:
Fix Released
Status in gcc-5 package in Ubuntu:
Fix Released
Status in gcc-4.8 source package in Trusty:
Fix Released
Bug description:
On Little Endian systems, GCC performs optimizations to remove
unnecessary element reversals of vectors that are sometimes required
to adjust for behavior of the lxvd2x, etc., instructions. In one not
uncommon case, such optimizations are defeated when we perform a
vector convert from double-precision to single-precision followed by a
vector splat word. I have pushed patches upstream to fix this,
implemented using the following revisions:
GCC trunk (6.0): 222351
GCC 5.1: 222394
GCC 4.9: 222420
GCC 4.8: 222427
I would like to see the backported patch applied to the gcc shipped
with the Ubuntu 15.10 release. We should probably have a conversation
about the next service pack for the 14.04 LTS release as well.
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