[llvm-dev] [LTO] Bypass the integrated assembler ...

[Umesh Kalappa via llvm-dev]

Thank you Paul,Amini and Kevin.

Your inputs ,helped us .

~Umesh

On Wed, Aug 10, 2016 at 8:51 AM, Mehdi Amini via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> On Aug 9, 2016, at 8:17 PM, Robinson, Paul <paul.robinson at sony.com> wrote:
>
> Otherwise you can also do something like what Kevin had in mind: ask
> LTOCodeGenerator to produce the bitcode before the backend and exit the
> linker process at this point, then run llc on it to get the assembly,
> assemble it, and re-invoke the linker.
> Or feed the emitted bitcode back into clang, without –flto, which would let
> you use all the normal clang ways to decide what kind of output you want.
> (Clang will accept .bc or .ll files as input.)  This also has the support
> advantage of not introducing developer tools into your application build
> workflow; whether this is important to you depends on who your users are and
> what tools you normally deliver to them.  (llc is generally not considered a
> tool appropriate to end-users.)
>
>
> Very good point indeed.
>
> —
> Mehdi
>
>
>
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Mehdi
> Amini via llvm-dev
> Sent: Tuesday, August 09, 2016 9:53 AM
> To: Kevin Choi
> Cc: LLVM Developers Mailing List
> Subject: Re: [llvm-dev] [LTO] Bypass the integrated assembler ...
>
>
>
> On Aug 9, 2016, at 9:24 AM, Kevin Choi via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>
> -Wl,--plugin=LLVMgold.so,--plugin-opt=emit-llvm
>
>
> This is totally Gold specific. The fact that he mentions using
> LTOCodeGenerator makes me think that he does not use Gold.
>
>
>
> http://llvm.org/docs/CommandGuide/opt.html
> http://llvm.org/docs/CommandGuide/llc.html
>
> "The llc command compiles LLVM source inputs into assembly language for a
> specified architecture."
>
> On 9 August 2016 at 04:16, Umesh Kalappa via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> Hi Guys ,
>
> We enabled the LTO on our code base and found that LTO uses the
> integrated/builtin assembler to emit the final optimized code .O
> (FileType= CGFT_ObjectFile) .
>
> Can we bypass this semantic ,for something like you emit .S  file
> (FileType=CGFT_AssemblyFile),
>
> Then we pass this  .S file to our native assembler and  the linker
> .....any switch/ options  do so ?
>
> i.e  something like as we have   "-no-integrated-as" for clang driver .
>
> Currently ,we thought of hacking the LTOCodeGenerator.cpp for the same .
>
> The bottom-line is that ,we need to use our native assembler ,not the
> builtin .
>
> Any thoughts on this ?
>
> Unfortunately there is no “ready-to-use” way, clang has a driver that can
> dump intermediate file (here the .s) and invoke a chain of commands. The
> linker plugin is not designed this way, it is invoked by the linker and
> given the input bitcode will produce one or multiple object files for the
> linker.
> What you want to do could be achieved by hacking the LTOCodeGenerator and do
> something like use posix_spawn and pipes to invoke your assembler.
> Otherwise you can also do something like what Kevin had in mind: ask
> LTOCodeGenerator to produce the bitcode before the backend and exit the
> linker process at this point, then run llc on it to get the assembly,
> assemble it, and re-invoke the linker. This is probably less convenient if
> you need to integrate with a build system.
>
> —
> Mehdi
>
>
>
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