> -----Original Message----- > From: Mark Mitchell [mailto:m...@codesourcery.com] > Sent: Monday, December 29, 2008 11:51 AM > To: Andrew Haley > Cc: Eric Botcazou; gcc@gcc.gnu.org; Georg-Johann Lay > Subject: Re: Odd performance regression with -Os > > Andrew Haley wrote: > > Eric Botcazou wrote: > >>> Thanks. Are you holding this because we're in Stage 3? > >> The patch was written very recently so I wanted to let it > go through a good > >> deal of internal testing. Moveover I haven't measured its > impact on anything > >> else than Ada benchmarks (and on a patched 4.3 branch). > If people think that > >> it would be worth having for the 4.4 release, I can port > it and conduct basic > >> testing with it on the mainline, but that's pretty much it. > > > > Well, it's a fairly nasty regression on embedded targets with no > > multiplier, where people are likely to use -Os. Sounds to me like > > it qualifies for 4.4 > > I agree.
I just tried Eric's patch <http://gcc.gnu.org/ml/gcc/2008-12/msg00330.html> for the AVR on 4.3.2 (patch slightly modified to patch against the 4.3.2 release) and tested with Andrew's original test case. The AVR is a perfect target to test this as it is an 8-bit embedded processor, there are a number of variants that do not have multiply instructions, and almost all applications are compiled with -Os. I compiled the original test case using -mmcu=at90usb82 -Os. It compiled to 15 instructions at 32 bytes, with a call to __mulhi3. With the patch, the test case compiled to 10 instructions at 20 bytes, and no call to libgcc. I haven't regtested the patch yet, but so far I like what I see. Thanks, Eric Weddington
