[llvm-dev] Suboptimal code generated by clang+llc in quite a common scenario (?)

[Danila Malyutin via llvm-dev]

Making the pointer const appears to be enough too.

--
Danila

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Jakub (Kuba) Kuderski via llvm-dev
Sent: Thursday, August 8, 2019 20:23
To: Joan Lluch <joan.lluch at icloud.com>
Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Suboptimal code generated by clang+llc in quite a common scenario (?)

You can add __builtin_assume(scscx == pp); if that's your invariant -- this causes the loads to be gone using the clang from trunk.

On Thu, Aug 8, 2019 at 1:01 PM Joan Lluch via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hi Tim and Alex

Thanks for your replies.

So just to make it clear for me: does this imply that there’s indeed no way on the current version to tell the compiler or Clang to optimize this?

Thanks,

Joan


> On 8 Aug 2019, at 18:30, Tim Northover via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
>
> On Thu, 8 Aug 2019 at 17:08, Alex Brachet-Mialot via llvm-dev
> <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
>> This might not be the workaround you want because it is only available in C, but you can use restrict to allow such optimizations.
>
> It also doesn't work in Clang unfortunately. We can only represent
> restrict on function arguments at the moment.
>
> Cheers.
>
> Tim.
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--
Jakub Kuderski
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