[llvm-dev] C++ JIT Compiler with LLVM on Windows 10 - part 5
Lang Hames via llvm-dev
llvm-dev at lists.llvm.org
Tue May 5 11:12:08 PDT 2020
Hi Emmanuel,
Thank you very much for these! I will check them out today and see what's
going on.
Regards,
Lang.
On Mon, Apr 27, 2020 at 8:35 PM Emmanuel Roche <roche.emmanuel at gmail.com>
wrote:
> Hi Lang,
>
> Thank you for your feedback on the blog post, please find below some
> additional inputs from my side on the comments you provided:
>
> > Regarding emulated TLS deactivation: I've never looking into how/whether
> this works on Windows. If it doesn't make sense to have it on by default
> there we can change the default for Windows targets.
>
> I'm really no expert, so you probably want to collect additional
> inputs/checks on this point, but yes, from my current perspective, it seems
> that it doesn't really work to try to use Emulated TLS in LLJIT on Windows,
> but one should keep in mind that this is when using the microsoft crt from
> Visual Studio (FYI, I'm using version 2017 for now, maybe it was different
> in previous versions too): I would expect things to be different if you are
> using another compiler as base (?) [I mean, if you change the default, this
> might then break previously working code that was based on mingw for
> instance... But not sure if this should be a concern or not for a not yet
> released version of LLVM ;-)]
>
> > I think that anything that llvm-link can merge should, in theory, be
> safe to add to the JIT. This actually sounds like a bug. Are you able to
> share the full modules that you were merging?
>
> Initially, the test I made on this point was using the Lest test framework
> as described in my post, but your feedback above got me thinking, and I
> could actually come up with a more simple setup without any C++ library
> dependency: this new test is simply based on a couple of C++ functions that
> are using exceptions. I used the attached lua script "exception3.lua" to
> generate the bitcode files and load the corresponding modules [of course I
> don't expect you to run lua scripts, but I thought that this could help
> understanding the code generation context anyway]. So with that script I
> generated the test_func1.bc/test_func2.bc/test_func1_and_func2.bc and the
> corresponding .ll file (generated from the .bc files using llvm-dis): all
> those files are attached to this email too.
>
> => So, I can load for instance the module corresponding to test_func1.bc
> in my main JITDylib, but then, if I try to load the test_func2 IR module in
> the same Dylib, I get the following error:
>
> *Duplicate definition of symbol '??_7exception at std@@6B@'*
>
> In all the .ll files you will find multiple references of that symbol...
> but unfortunately, my skills won't get me any further than that [=> ie. I
> have no idea what to think about the content of those files :-)].
>
> But anyway, if you notice anything interesting yourself, or you have an
> idea you think I should try, or you need more info on anything here please
> let me know.
>
> PS: I'm thinking maybe the command line arguments I'm providing to the
> compilerInvocation might also be important here so, just in case: here is
> the list of args I'm using currently:
>
> { "-triple=x86_64-pc-windows-msvc19.16.27030",
> "-x", "c++",
> "-mrelax-all",
> "-mincremental-linker-compatible",
> "-disable-free",
> "-discard-value-names",
> "-mrelocation-model", "pic",
> "-pic-level", "2",
> "-mthread-model", "posix",
> "-mframe-pointer=none",
> "-relaxed-aliasing",
> "-fmath-errno",
> "-fno-rounding-math",
> "-mconstructor-aliases",
> "-munwind-tables",
> "-target-cpu", "x86-64",
> "-mllvm",
> "-x86-asm-syntax=intel",
> "-stack-protector","2",
> "-fcxx-exceptions",
> "-fexceptions",
> "-fexternc-nounwind",
> "-fms-volatile",
> "-fdiagnostics-format", "msvc",
> "-dwarf-column-info",
> "-Wall",
> "-std=c++17",
> "-fdeprecated-macro",
> "-ferror-limit","19",
> "-fmessage-length=174",
> "-fms-extensions",
> "-fms-compatibility",
> "-fms-compatibility-version=19.16.27030",
> "-fdelayed-template-parsing",
> "-fcolor-diagnostics",
> "-fobjc-runtime=gcc",
> "-faddrsig",
> }
>
> Regards,
> Manu.
>
>
> Le lun. 27 avr. 2020 à 20:41, Lang Hames <lhames at gmail.com> a écrit :
>
>> I was just reading the blog post -- very cool!
>>
>> Regarding Globals construction & destruction: There definitely has been a
>> lot of churn in that area. There will probably be more before LLVM 11 is
>> released, but I can see light at the end of the tunnel. I think the Right
>> Way to run initializers in a JITDylib is to treat it as equivalent to a
>> dlopen operation (with extra allowances for the fact that new initializers
>> can be added to a JITDylib at runtime). This is what the LLJIT::initialize
>> method is doing. Now we just need to generalize it to support
>> out-of-process JITs. That will at least require a new remote-target
>> abstraction, and an RPC implementation for testing in-tree.
>>
>> Regarding emulated TLS deactivation: I've never looking into how/whether
>> this works on Windows. If it doesn't make sense to have it on by default
>> there we can change the default for Windows targets.
>>
>> Regarding merging of multiple modules:
>>
>> "But of course this would not work because as soon as I try to load the
>> second script, I get a duplicate symbol error from LLVM (and this
>> completely makes sense):
>>
>> [ERROR]: LLVM error: Duplicate definition of symbol '??_7success at lest
>> @@6B@'"
>>
>> I think that anything that llvm-link can merge should, in theory, be safe
>> to add to the JIT. This actually sounds like a bug. Are you able to share
>> the full modules that you were merging?
>>
>> Regards,
>> Lang.
>>
>>
>> On Mon, Apr 27, 2020 at 11:11 AM David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>>> +Lang for LLVM Orc things
>>>
>>> On Mon, Apr 27, 2020 at 3:34 AM Emmanuel Roche via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Hello LLVM developers!
>>>>
>>>> So, I'm continuing my journey with my toy C++ JIT compiler
>>>> implementation, and I wrote another article on the issues/solutions I've
>>>> been working on in the past few days, mainly:
>>>>
>>>> - Precompiled header handling,
>>>> - Emulated TLS desactivation,
>>>> - Globals construction & destruction,
>>>> - C++ exceptions handling,
>>>> - Multi modules linking,
>>>>
>>>> => In case this could be helpful to anyone, you will find this article
>>>> here:
>>>> http://wiki.nervtech.org/doku.php?id=blog:2020:0425_jit_compiler_part5_improvements
>>>>
>>>> And of course, if you have any questions for me, just let me know.
>>>>
>>>> Meanwhile, happy hacking everyone ;-)!
>>>>
>>>> Best regards,
>>>> Manu.
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>
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