Re: [Boost-users] LLVM bitcode for Boost libraries?

Subject: Re: [Boost-users] LLVM bitcode for Boost libraries?
From: Osman Zakir (osmanzakir90_at_[hidden])
Date: 2018-11-30 12:47:16

So can I pass that flag to b2 when building Boost and have it generate bitcode?  How do I configure the Boost.Build to use LLVM/Clang as the compiler toolchain, though?  On Windows, of course.
________________________________
From: degski <degski_at_[hidden]>
Sent: Friday, November 30, 2018 11:03 AM
To: boost-users_at_[hidden]
Cc: osmanzakir90_at_[hidden]
Subject: Re: [Boost-users] LLVM bitcode for Boost libraries?

On Thu, 29 Nov 2018 at 18:09, Osman Zakir via Boost-users <boost-users_at_[hidden]<mailto:boost-users_at_[hidden]>> wrote:
And what about how to generate LLVM bitcode for Boost libraries?  Can I do it with the bootstrapper tool that comes with the Boost distribution when we download Boost source files?

 I'm cross-posting this from the cfe-dev list [I know nothing about this, just that the questions seem to be the same]

Date: Thu, 29 Nov 2018 09:48:58 +0100
From: Alex Denisov via cfe-dev <cfe-dev_at_[hidden]<mailto:cfe-dev_at_[hidden]>>
To: David Greene <dag_at_[hidden]<mailto:dag_at_[hidden]>>
Cc: "cfe-dev_at_[hidden]<mailto:cfe-dev_at_[hidden]>" <cfe-dev_at_[hidden]<mailto:cfe-dev_at_[hidden]>>
Subject: Re: [cfe-dev] Getting LLVM IR from clang
Message-ID: <268D2CEC-AFC2-4F32-94FE-E445E882A00D_at_[hidden]<mailto:268D2CEC-AFC2-4F32-94FE-E445E882A00D_at_[hidden]>>
Content-Type: text/plain;       charset=us-ascii

Hi David,

There are at least two robust ways to get the Bitcode/IR:

1. LTO. You can enable link-time optimization by adding -flto compiler flags, in the end all object files (*.o) will in fact be bitcode files. I.e.:

    > file gmock.dir/gmock-gtest-all.cc.o
    gmock.dir/gmock-gtest-all.cc.o: LLVM bitcode, wrapper x86_6

2. Embedded bitcode. Clang 3.9 and higher has an option -fembed-bitcode. When enabled, the resulting executable will contain additional section containing bitcode.
You can use this great tool[1] to extract the bitcode from an executable.

Both approaches produce bitcode (binary format), if you need IR (human-readable format), then you can post-process the bitcode by running llvm-dis against each bitcode file.

I hope it helps.

[1] https://github.com/JDevlieghere/LibEBC

> On 28. Nov 2018, at 23:22, David Greene via cfe-dev <cfe-dev_at_[hidden]<mailto:cfe-dev_at_[hidden]>> wrote:
>
> How do I get the LLVM IR produced by clang?  I know that -emit-llvm
> produces IR but it seems to be after processing by LLVM (things are
> optimized out, for example).  Is there an "official" way to get the IR
> coming right out of clang's codegen?  I can do a hack with -mllvm
> -print-before-all but that's icky.
>
> Thanks!
>
>                          -David
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degski
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