[PATCH] D28126: [MemDep] Handle gep with zeros for invariant.group

[Jonas Devlieghere via Phabricator via llvm-commits]

JDevlieghere added inline comments.


================
Comment at: lib/Analysis/MemoryDependenceAnalysis.cpp:383-384
+      // U = bitcast Ptr  ||  U = getelementptr Ptr, 0, 0...
+      auto *BCI = dyn_cast<BitCastInst>(U);
+      auto *GEP = dyn_cast<GetElementPtrInst>(U);
+      if (BCI || (GEP && GEP->hasAllZeroIndices())) {
----------------
Prazek wrote:
> Prazek wrote:
> > chandlerc wrote:
> > > It would be nice to avoid going through the type lookup machinery twice here.
> > Code elegance your concern here right?
> > I can put it in ifs like
> > 
> >   if (isa<BitCastInst>(U)) {
> >     TryInsertToQueue(U);
> >     continue;
> >   }
> >   if (auto *GEP = dyn_cast<GetElementPtr>(U)) {
> >     if(GEP->hasAllZeroIndices())
> >       TryInsertToQueue(U);
> >     continue;
> >   }
> > 
> > I am not sure if it will be cleaner (specially because of nested if)
> > 
> >   
> >   
> 
> if (auto *GEP = dyn_cast<GetElementPtr>(U); GEP && GEP->hasAllZeroIndices()) {
>   TryInsertToQueue(U);
>   continue;
> }
> 
> This is exactly why I really would love to use C++17 in LLVM :)
Alternatively you could switch on `U->getOpcode()` and use a regular cast. This way you have to check the type only once, at the expense of adding more clutter. Wouldn't do it here though. 


https://reviews.llvm.org/D28126