D.gnu - Using Link Time Optimization (LTO)
- Mike (50/50) Mar 22 2014 Hello,
- Johannes Pfau (13/74) Mar 23 2014 Some time ago LTO was only supported by the gold linker, so you might
- Iain Buclaw (2/76) Mar 23 2014 I'd rather we'd fix the outstanding LTO bug before we start testing with...
- Mike (4/19) Mar 23 2014 You were right, I have to link with gcc to get LTO to kick in.
Hello,
I have some code generating the following assembly:
{OnReset}:
8000010: b508 push {r3, lr}
8000014: f000 f828 bl 8000068 <{MyFunction}>
8000018: e7fe b.n 8000018 <{OnReset}+0x8>
800001a: bf00 nop
08000068
{MyFunction}:
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}:
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
Mar 22 2014
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}
8000014: f000 f828 bl 8000068 <{MyFunction}>
8000018: e7fe b.n 8000018 <{OnReset}+0x8>
800001a: bf00 nop
08000068
{MyFunction}:
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}:
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 :-)
Mar 23 2014
Iain Buclaw <ibuclaw gdcproject.org> 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>:I'd rather we'd fix the outstanding LTO bug before we start testing with it. :o)Hello, I have some code generating the following assembly: {OnReset}: 8000010: b508 push {r3, lr} 8000014: f000 f828 bl 8000068 <{MyFunction}> 8000018: e7fe b.n 8000018 <{OnReset}+0x8> 800001a: bf00 nop 08000068 {MyFunction}: 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}: 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, MikeSome 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 :-)
Mar 23 2014
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!
Mar 23 2014