[llvm-dev] Preserving Call to Intrinsic function
Pierre-Andre Saulais via llvm-dev
llvm-dev at lists.llvm.org
Fri Jan 27 10:03:22 PST 2017
Hi Kumail,
That's strange.
When you are generating the .ll file from clang, do you have two
intrinsic calls in the IR?
If that's the case, I'd run llc with -print-after-all to identify which
LLVM pass removes the second call, and then debug the pass to see what
is going on.
Pierre-Andre
On 27/01/17 17:50, Kumail Ahmed wrote:
> Hi Pierre,
>
> Thank you for your swift response!
>
> I've tried almost everything that you mentioned, but it seems like
> LLVM simply doesn't care about the flags I pass to it.
>
> Best regards,
> Kumail Ahmed
>
> On Fri, Jan 27, 2017 at 6:05 PM, Pierre-Andre Saulais
> <pierre-andre at codeplay.com <mailto:pierre-andre at codeplay.com>> wrote:
>
> Hi Kumail,
>
> There is a flag that does what you are looking for (see
> Intrinsics.td for definitions):
>
> // IntrNoduplicate - Calls to this intrinsic cannot be duplicated.
> // Parallels the noduplicate attribute on LLVM IR functions.
> def IntrNoDuplicate : IntrinsicProperty;
>
> Another thing to check is whether your intrinsic is marked as
> having side-effects or not. Intrinsics with no side effects may be
> optimized by LLVM. If you inspect the DAG using llc, an intrinsic
> with side-effects should have a chain (blue dashed edge) going to
> and coming from its node:
>
> llc -O1 foo.ll -view-isel-dags
>
> If it doesn't, you can mark it as having side-effects using one of
> the following attributes:
>
> // IntrReadMem - This intrinsic only reads from memory. It does
> not write to
> // memory and has no other side effects. Therefore, it cannot be
> moved across
> // potentially aliasing stores. However, it can be reordered
> otherwise and can
> // be deleted if dead.
> def IntrReadMem : IntrinsicProperty;
>
> // IntrWriteMem - This intrinsic only writes to memory, but does
> not read from
> // memory, and has no other side effects. This means dead stores
> before calls
> // to this intrinsics may be removed.
> def IntrWriteMem : IntrinsicProperty;
>
> By default intrinsics returning void are assumed to have side effects.
>
> Pierre-Andre
>
>
> On 27/01/17 16:33, Kumail Ahmed via llvm-dev wrote:
>> Hello everyone,
>>
>>
>> Consider we have this following set of code:
>>
>> int foo() {
>>
>> int a,b;
>> a = __builtin_XX(0x11);
>> b = __builtin_XX(0x11);
>> return a+b;
>> }
>>
>> The problem currently is that LLVM eliminated the second call and
>> copied the result from the first call into a new set of
>> registers. Is there is a way to force LLVM to generate two
>> explicit calls to a builtin function. The builtin takes in an
>> integer type, and also returns back an integer type:
>>
>> def int_XX : GCCBuiltin<"__builtin_XX">,
>> Intrinsic<[llvm_i32_ty], [llvm_i32_ty]>;
>>
>> Is there some flag that I'm missing? Your help will be really
>> appreciated.
>>
>>
>> Best Regards,
>> Kumail Ahmed
>>
>>
>>
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>
> --
> Pierre-Andre Saulais
> Principal Software Engineer, Compilers
> Codeplay Software Ltd
> Level C Argyle House, 3 Lady Lawson Street, Edinburgh, United Kingdom, EH3 9DR
> Tel: +44 (0)131 466 0503 <tel:+44%20131%20466%200503>
> Website: http://www.codeplay.com
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>
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> --
> Best Regards, Kumail Ahmed M.Sc. Student TU Kaiserslautern
--
Pierre-Andre Saulais
Principal Software Engineer, Compilers
Codeplay Software Ltd
Level C Argyle House, 3 Lady Lawson Street, Edinburgh, United Kingdom, EH3 9DR
Tel: +44 (0)131 466 0503
Website: http://www.codeplay.com
Twitter: https://twitter.com/codeplaysoft
This email and any attachments may contain confidential and /or privileged information and is for use by the addressee only. If you are not the intended recipient, please notify Codeplay Software Ltd immediately and delete the message from your computer. You may not copy or forward it, or use or disclose its contents to any other person. Any views or other information in this message which do not relate to our business are not authorized by Codeplay software Ltd, nor does this message form part of any contract unless so stated.
As internet communications are capable of data corruption Codeplay Software Ltd does not accept any responsibility for any changes made to this message after it was sent. Please note that Codeplay Software Ltd does not accept any liability or responsibility for viruses and it is your responsibility to scan any attachments.
Company registered in England and Wales, number: 04567874
Registered office: Regent House, 316 Beulah Hill, London, United Kingdom, SE19 3HF
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