[llvm-dev] Skip redundant checks in AliasSet::aliasesUnknownInst

[Philip Reames via llvm-dev]

In addition to this, see my comments on the bug.  LICM is using AST in a 
particular usage pattern when most of the work done by add(AST&) ends up 
being redundant for perfectly nested loops.

Philip

On 01/24/2016 09:44 AM, Daniel Berlin via llvm-dev wrote:
> It sounds like UnknownInsts should really be a SmallSet, SmallPtrSet, 
> or DenseSet (if you can't do the others).
>
> Otherwise, even with your patch, we are still wasting time traversing 
> and copying and .... the unknown instructions.
>
> If that doesn't work, I suspect the way you get dupes is through 
> mergeSetIn, so you also could probably just change:
>
> 00061   }else  if  (ASHadUnknownInsts) {
> 00062     UnknownInsts.insert(UnknownInsts.end(), AS.UnknownInsts.begin(), AS.UnknownInsts.end());
> 00063     AS.UnknownInsts.clear();
> 00064   }
>
>
> You could insert the current unknown insts into a smallptrset, and 
> then only append them to UnknownInsts if they aren't in the set.
>
> This should remove your dupes.
>
>
>
> On Sun, Jan 24, 2016 at 5:28 AM, Roman Gareev via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     Dear llvm contributors,
>
>     Could you please advise me how to skip
>     checks, which are performed in AliasSet::aliasesUnknownInst, of
>     unknown instructions from different alias sets of an alias set tracker
>     that is a parameter of ‘AliasSetTracker::add(const AliasSetTracker
>     &AST)’?
>
>     If this wasn’t available at the moment and someone could review me, I
>     would try to implement it. A temporary patch can be found attached
>     (for example, ViewedInst can become a second parameter of
>     AliasSetTracker::addUnknown ). It
>     passes the LLVM regression tests and helps to reduce the runtime of
>     'opt -basicaa -licm out.opt.ll’ from 130ms to 67ms and the runtime of
>     'opt -basicaa -licm out.opt2.ll’ from 117ms to 62ms (out.opt.ll and
>     out.opt2.ll can be found on the following link
>     https://llvm.org/bugs/show_bug.cgi?id=23077).
>
>     Thank you for the attention!
>
>     --
>                                         Cheers, Roman Gareev.
>
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>
>
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