llvm dev - May 2018 - Four bitcode generated with plugin-opt=save-temps

Hi

I use the LDFLAGS=" -flto -fuse-ld=gold  -Wl,-plugin-opt=save-temps "
to
generate the makefile and to make the whole program. However,  found four
different kinds of bitcode for each target. For example, I am compiling
coreutils. For the program "nohup", I can get

 nohup.0.0.preopt.bc
 nohup.0.2.internalize.bc
 nohup.0.4.opt.bc
 nohup.0.5.precodegen.bc

If I am right, I can also get the bitcode with emit-llvm option in clang.
May I know which bc among the above four should be the same as the one I
generated with emit-llvm. More information are very thankful.

Regards
Muhui
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These are the bitcode at different stages of the LTO portion of the
compile. LTO merges the IR for all files being linked and optimizes them as
a single monolithic module. The preopt.bc is the merged IR just after
merging and before performing any LTO optimizations. internalize.bc is
after performing whole program internalization. opt.bc is after the
optimization pipeline, and .precodegen.bc is immediately before native code
generation.

The emit-llvm option will give you the IR for a single source file when you
compile it with -c. All of those files when combined give the IR in the
preopt.bc temp file.

Hope that helps,
Teresa

On Tue, May 15, 2018 at 4:43 AM Muhui Jiang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi
>
> I use the LDFLAGS=" -flto -fuse-ld=gold  -Wl,-plugin-opt=save-temps
" to
> generate the makefile and to make the whole program. However,  found four
> different kinds of bitcode for each target. For example, I am compiling
> coreutils. For the program "nohup", I can get
>
>  nohup.0.0.preopt.bc
>  nohup.0.2.internalize.bc
>  nohup.0.4.opt.bc
>  nohup.0.5.precodegen.bc
>
> If I am right, I can also get the bitcode with emit-llvm option in clang.
> May I know which bc among the above four should be the same as the one I
> generated with emit-llvm. More information are very thankful.
>
> Regards
> Muhui
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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Hi Teresa

Thanks for your very quick and clear explanation. I have one more question.

The emit-llvm option will give you the IR for a single source file when you
compile it with -c. All of those files when combined give the IR in the
preopt.bc temp file.
==========So if I use "clang -emit-llvm -c" to generate the .ll file.
It should be
the same as the one I generated by using "llvm-dis *.preopt.bc -o
*.preopt.ll" to translate the bitcode to IR. Actually, I would like to
obtain the control flow information from the LLVM IR. Will different stages
of the bitcode influence the generated CFG?
Many Thanks

Regards
Muhui

2018-05-15 21:19 GMT+08:00 Teresa Johnson <tejohnson at google.com>:
> These are the bitcode at different stages of the LTO portion of the
> compile. LTO merges the IR for all files being linked and optimizes them as
> a single monolithic module. The preopt.bc is the merged IR just after
> merging and before performing any LTO optimizations. internalize.bc is
> after performing whole program internalization. opt.bc is after the
> optimization pipeline, and .precodegen.bc is immediately before native code
> generation.
>
> The emit-llvm option will give you the IR for a single source file when
> you compile it with -c. All of those files when combined give the IR in the
> preopt.bc temp file.
>
> Hope that helps,
> Teresa
>
> On Tue, May 15, 2018 at 4:43 AM Muhui Jiang via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi
>>
>> I use the LDFLAGS=" -flto -fuse-ld=gold 
-Wl,-plugin-opt=save-temps " to
>> generate the makefile and to make the whole program. However,  found
four
>> different kinds of bitcode for each target. For example, I am compiling
>> coreutils. For the program "nohup", I can get
>>
>>  nohup.0.0.preopt.bc
>>  nohup.0.2.internalize.bc
>>  nohup.0.4.opt.bc
>>  nohup.0.5.precodegen.bc
>>
>> If I am right, I can also get the bitcode with emit-llvm option in
clang.
>> May I know which bc among the above four should be the same as the one
I
>> generated with emit-llvm. More information are very thankful.
>>
>> Regards
>> Muhui
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>  408-460-2413
>
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