[LLVMdev] Proposal for ""llvm.mem.vectorize.safelen"

[Humphreys, Jonathan]

Yes, I think the 2 outcomes are:
 - the current spec is unclear and will be clarified
 - in order to support safelen() and even the simd construct itself, LLVM will require infrastructure work to know when a lexically backwards dependence may have been introduced.

Jon

-----Original Message-----
From: Tian, Xinmin [mailto:xinmin.tian at intel.com] 
Sent: Monday, September 29, 2014 10:43 AM
To: Renato Golin; Hal Finkel
Cc: Humphreys, Jonathan; Robison, Arch; LLVM Dev
Subject: RE: [LLVMdev] Proposal for ""llvm.mem.vectorize.safelen"

Renato, I think Hal meant to ensure partial ordering, e.g. not to convert lexical forward data dep to lexical backward data dep due to statement ordering if any. 
'
Xinmin 

-----Original Message-----
From: Renato Golin [mailto:renato.golin at linaro.org] 
Sent: Monday, September 29, 2014 1:06 AM
To: Hal Finkel
Cc: Tian, Xinmin; Jonathan Humphreys; Robison, Arch; LLVM Dev
Subject: Re: [LLVMdev] Proposal for ""llvm.mem.vectorize.safelen"

On 28 September 2014 22:09, Hal Finkel <hfinkel at anl.gov> wrote:
> Thanks Xinmin!
>
> So we'll need a method to ensure the correct (partial) ordering.

I thought that the idea was to avoid computing loop dependencies when safelen is specified, at least at that level. We might do it to a greater length, but we should assume it to be safe for distances < VL.

We still need the method, I agree, for everything else, though.

cheers,
--renato