Am Sun, 23 Mar 2014 02:14:20 +0000
schrieb "Mike" <n...@none.com>:
> Hello,
>
> I have some code generating the following assembly:
> {OnReset}:
> 8000010: b508 push {r3, lr}
> 8000012: 20ff movs r0, #255 ; 0xff
> 8000014: f000 f828 bl 8000068 <{MyFunction}>
> 8000018: e7fe b.n 8000018 <{OnReset}+0x8>
> 800001a: bf00 nop
>
> 08000068
> {MyFunction}:
> 8000068: f44f 5380 mov.w r3, #4096 ; 0x1000
> 800006c: f2c2 0300 movt r3, #8192 ; 0x2000
> 8000070: 7018 strb r0, [r3, #0]
> 8000072: 4770 bx lr
>
> "MyFunction" and "OnReset" are in different source files and
> therefore compiled to different object files. I would like to
> get "MyFunction" fully inlined to "OnReset" to remove the extra
> branch instructions (bl and bx).
>
> It's my understanding that because the two functions are compiled
> into separate object files, this must be done using LTO. If I
> compile them into the same object file, I get the full inlining
> I'm looking for, but that's not going to scale well for my
> project.
>
> ** Beautiful, isn't it? **
> {OnReset}:
> 8000010: f44f 5380 mov.w r3, #4096 ; 0x1000
> 8000014: f2c2 0300 movt r3, #8192 ; 0x2000
> 8000018: 22ff movs r2, #255 ; 0xff
> 800001a: 701a strb r2, [r3, #0]
> 800001c: e7fe b.n 800001c <{OnReset}+0xc>
> 800001e: bf00 nop
>
>
> I've tried adding -flto to my compiler and linker flags and a
> number of other things without success. The compiler seems to
> generate extra information in my object files, but the linker
> doesn't seem to do the optimization. I don't get any ICEs,
> however, as stated in Bug 61 and 88. I just don't get the result
> I'm after.
>
> Here are my compiler commands:
> arm-none-eabi-gdc -mthumb -mcpu=cortex-m4 -fno-emit-moduleinfo
> -ffunction-sections -fdata-sections -O3 -c -flto ...
> arm-none-eabi-ld -T link/link.ld -Map binary/memory.map
> --gc-sections -flto ...
>
> I'm using my arm-none-eabi cross toolchain built from the GDC 4.8
> branch. I tried adding --enable-lto to my toolchain's configure,
> but that had no effect. It's my understanding that it's enabled
> by default anyway.
>
> Does anyone know how I can get this level of inlining without
> compiling all my source into one object file?
>
> Thanks for any help,
> Mike
Some time ago LTO was only supported by the gold linker, so you might
need to configure binutils with --enable-gold --enable-plugins
--enable-lto
GCC should also be compiled with --enable-gold --enable-plugins
--enable-lto
http://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Optimize-Options.html
also says if you link manually you must use gcc to link, not ld and
pass -flto when linking as well:
gcc -o myprog -flto -O2 foo.o bar.o
You can also try passing -fuse-linker-plugin to all gcc commands.
I never used LTO though, so I'm not sure if this will actually help :-)
