[llvm-dev] llvm optimizer turning musttail into tail

[Carlo Kok via llvm-dev]

That looks like it should work, but seems to check the callee only, not 
the call itself, so :

   musttail call void bitcast (i32 (i32, i8*, %"Type"*)* @"Method" to 
void (i32, i8*)*)(i32 %0, i8* %1) #3

attributes #3 = { "thunk"="true" }

doesn't work, and I can't place this on the actual method, since that 
one isn't a thunk.

On 2016-11-27 21:57, David Majnemer wrote:
> Try using the "thunk"
> attribute: http://llvm.org/docs/LangRef.html#function-attributes
>
> InstCombine has logic to avoid getting rid of the cast in such
> situations: https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/InstCombineCalls.cpp#L2821
>
>
>
> On Sun, Nov 27, 2016 at 7:40 AM, Carlo Kok <ck at remobjects.com
> <mailto:ck at remobjects.com>> wrote:
>
>     Inst combine yes. However it shouldn't drop this bit cast in the
>     first place, since the last parameter isn't available. (It only
>     works because of this must tail)
>
>
>     On 27 November 2016 01:37:43 CET, Sean Silva <chisophugis at gmail.com
>     <mailto:chisophugis at gmail.com>> wrote:
>
>         r287955 seems like it might be related.
>
>         -- Sean Silva
>
>         On Sat, Nov 26, 2016 at 4:06 PM, Sean Silva
>         <chisophugis at gmail.com <mailto:chisophugis at gmail.com>> wrote:
>
>             This sounds buggy to me. What pass is doing this?
>
>             -- Sean Silva
>
>             On Thu, Nov 24, 2016 at 5:39 AM, Carlo Kok via llvm-dev
>             <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
>             wrote:
>
>
>                 I've got some calls like:
>
>                 musttail call void bitcast (i32 (i32, i8*, %Type*)*
>                 @MyMethod to void (i32, i8*)*)(i32 %0, i8* %1)
>                 ret void
>
>                 Into something like:
>                 %8 = tail call i32 @MyMethod(i32 %0, i8* %1, %Type* null)
>                 ret void
>
>                 I realize I'm losing a parameter there, but this is an
>                 interface jump trick I use and relies on the end code
>                 being a 'jmp' (x86). I realize i can probably use noopt
>                 & noinline to do this trick, but I do want llvm to
>                 optimize and inline calls if it can prove it always
>                 calls a given method. Any way i can do this?
>
>                 --
>                 Carlo Kok
>                 RemObjects Software
>                 _______________________________________________
>                 LLVM Developers mailing list
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>
>
>
>
>     --
>     Carlo Kok
>     RemObjects Software
>
>

-- 
Carlo Kok
RemObjects Software