Re: [avr-gcc-list] binutils 2.22 blow up program size with -flto

[Weddington, Eric]

Hi Volker

There are known issues with LTO and AVR, though unknown reasons why. For now I 
would suggest that you avoid that feature.

However, please file a bug report at the GCC Bugzilla database. That way we can 
keep track of the various LTO issues and eventually try to get them fixed.

Thanks,
Eric Weddington

> -----Original Message-----
> From: address@hidden [mailto:avr-
> address@hidden On Behalf Of Volker
> Kuhlmann
> Sent: Saturday, July 28, 2012 9:44 PM
> To: address@hidden
> Subject: [avr-gcc-list] binutils 2.22 blow up program size with -flto
> 
> I am finding that with binutils 2.22 and newer gcc the program size goes
> through the roof:
> 
> Tested with Seismograph 1.8.3, avr-libc 1.7.1 with progmem const patch,
> binutils 2.22 or 2.19.1 (indicated by bin219),
> avr-gcc flags (the nolto are missing -flto)
>     -mmcu=atmega328p -Os -ffunction-sections -fdata-sections -mrelax -flto
>     -g2 -gstabs -std=gnu++0x
> 
>   text   data  bss    dec   hex filename
>  21156    752  967  22875  595b output/Seismograph-183-436.elf
>  21156    752  967  22875  595b output/Seismograph-183-436-bin219.elf
> 
>  22742   1008  960  24710  6086 output/Seismograph-183-463.elf
>  20730    750  966  22446  57ae output/Seismograph-183-463-bin219.elf
>  21088    750  967  22805  5915 output/Seismograph-183-463-nolto.elf
>  21088    750  967  22805  5915 output/Seismograph-183-463-bin219-nolto.elf
> 
>  22016    748  960  23724  5cac output/Seismograph-183-471.elf
>  21144    746  966  22856  5948 output/Seismograph-183-471-bin219.elf
>  21278    746  967  22991  59cf output/Seismograph-183-471-nolto.elf
>  21278    746  967  22991  59cf output/Seismograph-183-471-bin219-nolto.elf
> 
> What could be the reason for this?
> gcc was recompiled for each binutils version.
> 
> The other sad thing is that gcc 4.7.1 does not improve code size over
> 4.3.6, and matches it only with binutils 2.19.1 and no LTO, otherwise
> being significantly worse. That's rather unexpected. Why could this be?
> 
> The combination of binutils 2.22, gcc 4.6.3 and LTO produces a broken
> program - never mind that for now. It's also the largest code size ever.
> 
> I'm still trying to get the optimum out of LTO, so far gcc 4.6.3 with
> binutils 2.19.1 and LTO gets top by far.
> 
> Any hints thanksfully received,
> 
> Volker
> 
> --
> Volker Kuhlmann                       is list0570 with the domain in header.
> http://volker.dnsalias.net/   Please do not CC list postings to me.
> 
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