[LLVMdev] [llvm-commits] [llvm] r160610 - /llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp

[Kaylor, Andrew]

Hi Takumi,

I'm a bit confused as to what is supposed to happen in the cross building scenarios.  For instance, if host=x86_64-linux and target=i686-mingw32, what should the MCJIT tests do?  Should they be suppressed because the architectures don't match?  If so, what about the case where host=x86_64-linux and target=x86_64-mingw32?

I'm modifying the MCJIT tests so that they will provide an explicit target triple on the run line.  In the case where the host OS is Windows, I'm appending "-elf" to the target triple.  I think that should be sufficient to make things work in the cases where the host triple and the target triple are compatible, and then I can suppress the cases where host and target aren't compatible in the lit.local.cfg file.

Does that sound right?

My concern is that I don't quite know how to predict what will happen on some of the buildbots aside from checking something in and seeing what happens.  Hopefully any obvious problems will be caught in code review.

Aside from the testing, it seems to me that TargetSelect should always use the Module target triple, and if it isn't compatible with the host environment then it will just fail.

-Andy

-----Original Message-----
From: NAKAMURA Takumi [mailto:geek4civic at gmail.com] 
Sent: Tuesday, September 11, 2012 5:13 PM
To: Kaylor, Andrew
Cc: llvm-commits at cs.uiuc.edu; llvmdev
Subject: Re: [llvm-commits] [llvm] r160610 - /llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp

Andy,

Yes, it was wrong, as long as RemoteTarget is available for the target.

If you would revert it, please consider then;

  - non-MCJIT stuff
  - Running different environment on the JIT
    e.g.) --build=--host=i686-linux --target=x86_64-linux
  - Host-incapable target on the JIT
    e.g.) --build=--host=x86_64-linux ---target=i686-mingw32

If JIT is unavailable for the default target, tests in test/ExecutionEngine and unittests/ExecutionEngine/JIT should be suppressed. My r160610 intended to tweak tests on cross targets (not to suppress, but to appease).

I wonder if we should honor the triple in Module, though.

Feel free to update, unless breaking tests, thank you.

...Takumi


2012/9/12 Kaylor, Andrew <andrew.kaylor at intel.com>:
> Hi,
>
> I realize that this is an old commit, but I just came across a problem related to this change and was hoping to enquire as to the rationale here.
>
> It is possible to provide a target triple to lli via the '-mtriple' command line option.  However, as a result of the change below, the user specified triple gets ignored in favor of LLVM_HOSTTRIPLE.  This seems wrong.
>
> I recognize that problems can arise if you try to use a target other than the default host triple with JIT or MCJIT.  However, with MCJIT it may be desirable to provide an environment string via the triple to generate MachO or ELF objects on platforms that wouldn't normally use those formats.  In particular, I am working on adding support for generating ELF objects on Windows (because COFF isn't supported by MCJIT).
>
> The change below prevents that.  As such, I would like to revert this change, or at least modify this to pick-up the environment from the module's target triple.
>
> Does that seem reasonable?
>
> -Andy
>
>
> -----Original Message-----
> From: llvm-commits-bounces at cs.uiuc.edu 
> [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of NAKAMURA Takumi
> Sent: Saturday, July 21, 2012 8:05 PM
> To: llvm-commits at cs.uiuc.edu
> Subject: [llvm-commits] [llvm] r160610 - 
> /llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp
>
> Author: chapuni
> Date: Sat Jul 21 22:04:57 2012
> New Revision: 160610
>
> URL: http://llvm.org/viewvc/llvm-project?rev=160610&view=rev
> Log:
> ExecutionEngine/TargetSelect.cpp: Override default triple as LLVM_HOSTTRIPLE.
>
> In current implementation, JIT should run only on host.
>
> Modified:
>     llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp
>
> Modified: llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/Tar
> getSelect.cpp?rev=160610&r1=160609&r2=160610&view=diff
> ======================================================================
> ========
> --- llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp (original)
> +++ llvm/trunk/lib/ExecutionEngine/TargetSelect.cpp Sat Jul 21 
> +++ 22:04:57
> +++ 2012
> @@ -26,7 +26,7 @@
>  using namespace llvm;
>
>  TargetMachine *EngineBuilder::selectTarget() {
> -  Triple TT(M->getTargetTriple());
> +  Triple TT(LLVM_HOSTTRIPLE);
>    return selectTarget(TT, MArch, MCPU, MAttrs);  }