[ACTIVITY] 13th - 19th February

Andrew Stubbs andrew.stubbs at linaro.org
Mon Feb 20 09:34:42 UTC 2012


* Linaro GCC

Discovered that part of my conditional execution problems were caused by 
some over-zealous peephole optimizations adding CC register clobbers to 
arithmetic operations in order to take advantage of the 16-bit encoding. 
This is a problem because they can't be converted to conditional 
execution so freely because overwriting the CC register prevents any 
further conditional execution (and forces a 32-bit encoding 
unnecessarily). I wrote a patch to help ifcvt unpick all this and DTRT, 
and posted it upstream. It turns out that Benrd (I think) already 
reimplemented the peephole optimization in the reorg pass, so all that 
is really needed is to delete the now obsolete peepholes. Richard E has 
approved the revised patch. Unfortunately I've now discovered that that 
exposed a bug in the machine description, so that'll have to be fixed also.

Tried to update the gcc-linaro/4.7 branch, but found the build broken. 
In fact, Matthias had already reported it to Bugzilla. I did a binary 
search, identified the problem commit, posted the info to bugzilla, and 
pushed a merge request for the last working commit for testing. This 
tested ok, so I've merged it to the Linaro 4.7 trunk.

Brought the Linaro GCC patch tracker up to date to aid identification of 
patches we will need to forward port to 4.7. The remaining 'red' patches 
are either not committed upstream, or I wasn't sure.

Attempted to benchmark the 64-bit shift improvements, but the target 
board (ursa1) has developed an I/O error.



* Other

Joe Seymour and I went to HP Bristol to attend one of their science 
lectures. Professor Jim Al-Khalili gave a talk about the recent 
"faster-than-light" neutrinos experiments, and explained why it can't 
possibly be true.
http://www.jimal-khalili.com/blog/faster-than-the-speed-of-light.html



More information about the linaro-toolchain mailing list