[PATCH] D89149: [SelectionDAG] Fix alias checking with potential later stack reuse

[Yonghong Song via llvm-commits]

On 12/1/20 5:44 AM, Nirav wrote:
> I've checked that I've permission with my current employer to 
> contribute code, so now I just need to find time to resurrect a 
> working repo on a reasonable machine which will probably need to wait 
> until the end of this month.
> 
> If you're inclined to look at it deeper in the meanwhile, I did look at 
> the cases to consider and I think the fix should just be on line 22262 
> where we're removing the dependence between two memory operations if the 
> locations don't alias (which now needs to check they're referring 
> potentially aliasable frames).

Thanks Nirav for the pointer. At the same time, I will also take a look 
at this piece of code.

> 
> case ISD::LIFETIME_START 
> <https://llvm.org/doxygen/namespacellvm_1_1ISD.html#a22ea9cec080dd5f4f47ba234c2f59110aada0b926e7ebc2bc55d158d4c37bdcca>:
> 22259 case ISD::LIFETIME_END 
> <https://llvm.org/doxygen/namespacellvm_1_1ISD.html#a22ea9cec080dd5f4f47ba234c2f59110ab49301b20458a7f312a0919e3c8abdb2>: 
> {
> 22260 // We can forward past any lifetime start/end that can be proven 
> not to
> 22261 // alias the memory access.
> 22262 if (!isAlias(N, C 
> <https://llvm.org/doxygen/NVVMIntrRange_8cpp.html#a2ae53ee71b2ccbb52b883c0b4f59f8c2>.getNode())) 
> {
> 22263 // Look further up the chain.
> 22264 C 
> <https://llvm.org/doxygen/NVVMIntrRange_8cpp.html#a2ae53ee71b2ccbb52b883c0b4f59f8c2> 
> = C 
> <https://llvm.org/doxygen/NVVMIntrRange_8cpp.html#a2ae53ee71b2ccbb52b883c0b4f59f8c2>.getOperand 
> <https://llvm.org/doxygen/classllvm_1_1User.html#abe1de1520a21f77ac57cc210bf0fb0b4>(0);
> 22265 return true;
> 22266  }
> 
> 
> On Tue, Dec 1, 2020 at 2:38 AM Yonghong Song via Phabricator 
> <reviews at reviews.llvm.org <mailto:reviews at reviews.llvm.org>> wrote:
> 
>     yonghong-song added a comment.
> 
>      > As an alternative, we could update ImproveChain (and
>     visitLIFETIME_END) to limit the aliasing
>      > around lifetime_start / end to disallow improving the chain
>     dependence of a mem op node
>      >  from a different lifetime node that may alias. That should
>     prohibit access from two aliasable
>      > frame indices from being concurrent while still allowing us to
>     leverage that disjoint allocs should be disjoint.
> 
>     @niravd Any update on this?
> 
> 
>     Repository:
>        rG LLVM Github Monorepo
> 
>     CHANGES SINCE LAST ACTION
>     https://reviews.llvm.org/D89149/new/
>     <https://reviews.llvm.org/D89149/new/>
> 
>     https://reviews.llvm.org/D89149
>     <https://reviews.llvm.org/D89149>
>