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

Am Sun, 23 Mar 2014 02:14:20 +0000
schrieb "Mike" <none@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 :-)

On 23 March 2014 07:49, Johannes Pfau <nospam@example.com> wrote:
> Am Sun, 23 Mar 2014 02:14:20 +0000
> schrieb "Mike" <none@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 :-)

I'd rather we'd fix the outstanding LTO bug before we start testing with it. :o)

On Sunday, 23 March 2014 at 07:51:14 UTC, Johannes Pfau wrote:
>
> 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 :-)

You were right, I have to link with gcc to get LTO to kick in.  And sure enough Bug 88 symptoms appeared.  At least I now know why nothing was happening.  Thank you!