Hi, I'm trying to generate some SPARCv8 assembly for a sparc target that doesn't have an FPU. I'm unable to get the flow to generate calls to a soft-float library. Since I wasn't able to find a definitive answer, I was hoping someone might be able to offer some pointers or shed some light. Running "clang -c -emit-llvm -msoft-float test.c -o test.bc" doesn't generate IR with soft-float library calls (perhaps understandably) - only hard float instructions. I would expect the frontend to at least be able to generate the library calls even though I'm not asking it to link to any library yet. Running "llc -march=sparc -soft-float test.bc -o test.s" next still does not replace the hard float instructions with soft-float calls. Is this a known issue, am I doing something wrong, etc.? Just as a test, I see that running "llc -march=arm -soft-float test.bc -o test.s" will indeed generate the appropriate soft-float library call. I checked using mips, x86, ppc32, etc. and it seems that only the arm target actually generates the soft-float call. Is there a reason many of the backend targets will not generate the library call? Is there some way to fix this? Thanks, Eric -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140923/cabff5cd/attachment.html>
Hi Eric,> Running "clang -c -emit-llvm -msoft-float test.c -o test.bc" doesn't generate IR with soft-float library calls (perhaps understandably) - only hard float instructions. I would expect the frontend to at least be able to generate the library calls even though I'm not asking it to link to any library yet.I think you have to explicitly pass the target. For an example: ./clang -c -emit-llvm -msoft-float test.c -o test.bc -### Does not show -msoft-float passed into the backend. Whereas the following invocation does: ./clang -target sparc-none-linux-gnu -c -emit-llvm -msoft-float test.c -o test.bc -### May be give this a try and see if it produces the correct lib calls? I happened to be working on something related (for ARM). - Asiri -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2557590 ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2548782
And, Apologies for the footer. Wrong account. Best, - Asiri -----Original Message----- From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Asiri Rathnayake Sent: 25 September 2014 10:48 To: Eric Cheng; llvmdev at cs.uiuc.edu Subject: Re: [LLVMdev] Support for Soft-float Hi Eric,> Running "clang -c -emit-llvm -msoft-float test.c -o test.bc" doesn'tgenerate IR with soft-float library calls (perhaps understandably) - only hard float instructions. I would expect the frontend to at least be able to generate the library calls even though I'm not asking it to link to any library yet. I think you have to explicitly pass the target. For an example: ./clang -c -emit-llvm -msoft-float test.c -o test.bc -### Does not show -msoft-float passed into the backend. Whereas the following invocation does: ./clang -target sparc-none-linux-gnu -c -emit-llvm -msoft-float test.c -o test.bc -### May be give this a try and see if it produces the correct lib calls? I happened to be working on something related (for ARM). - Asiri -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2557590 ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2548782 _______________________________________________ LLVM Developers mailing list LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
Hi Asiri,
Unfortunately, I had also tried using the -target switch previously
("-target sparc", "-target arm", etc.). However, since it
ultimately made
difference, I left it out of my example for brevity.
Thanks,
Eric
On Thu, Sep 25, 2014 at 3:02 AM, Asiri Rathnayake <asiri.rathnayake at
arm.com>
wrote:
> And, Apologies for the footer. Wrong account.
>
> Best,
>
> - Asiri
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On
> Behalf Of Asiri Rathnayake
> Sent: 25 September 2014 10:48
> To: Eric Cheng; llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] Support for Soft-float
>
> Hi Eric,
>
> > Running "clang -c -emit-llvm -msoft-float test.c -o test.bc"
doesn't
> generate IR with soft-float library calls (perhaps understandably) - only
> hard float instructions. I would expect the frontend to at least be able to
> generate the library calls even though I'm not asking it to link to any
> library yet.
>
> I think you have to explicitly pass the target. For an example:
>
> ./clang -c -emit-llvm -msoft-float test.c -o test.bc -###
>
> Does not show -msoft-float passed into the backend. Whereas the following
> invocation does:
>
> ./clang -target sparc-none-linux-gnu -c -emit-llvm -msoft-float test.c -o
> test.bc -###
>
> May be give this a try and see if it produces the correct lib calls?
>
> I happened to be working on something related (for ARM).
>
> - Asiri
>
> -- IMPORTANT NOTICE: The contents of this email and any attachments are
> confidential and may also be privileged. If you are not the intended
> recipient, please notify the sender immediately and do not disclose the
> contents to any other person, use it for any purpose, or store or copy the
> information in any medium. Thank you.
>
> ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ,
> Registered in England & Wales, Company No: 2557590
> ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ,
> Registered in England & Wales, Company No: 2548782
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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On 24 September 2014 07:02, Eric Cheng <eccheng at stanford.edu> wrote:> Running "clang -c -emit-llvm -msoft-float test.c -o test.bc" doesn't > generate IR with soft-float library calls (perhaps understandably) - only > hard float instructions. I would expect the frontend to at least be able to > generate the library calls even though I'm not asking it to link to any > library yet.Hi Eric, If you mean "IR floating point instructions", than this is correct. The front-end doesn't know what the back-end is capable of (hard multiply, divide etc), so it emits "fp instructions" and the back-end will then generate the correct call/instruction for each separate case.> Running "llc -march=sparc -soft-float test.bc -o test.s" next still does not > replace the hard float instructions with soft-float calls. Is this a known > issue, am I doing something wrong, etc.?Maybe the Sparc back-end is not able (or willing) to transform the instructions into library calls. The ARM back-end certainly does.> Is there a reason many of the backend targets will not generate the library > call? Is there some way to fix this?It may be that they never found it relevant? Or that your options is not correctly propagated (as Asiri commented). Looking at X86ISelLowering.cpp, there aren't that many calls to setLibcallName(), which there are zillions for ARM. The Sparc back-end has more than the X86, but mostly to round numbers and convert from FP to Int and vice-versa, so I doubt it'll ever call a library function to multiply or divide floating points. If that's the only problem, the way to fix this is to repeat the pattern in the ARM back-end, and add *all* library call hooks and make sure they're called when -msoft-float is specified. Also, if you do so, please add as many tests as necessary to make sure both soft and hard float are covered correctly. cheers, --renato