GVN-hoist: invalidate MD cache (PR29144)

[sebpop]

Summary

Without invalidating the entries in the MD cache we would try to access instructions
that were removed in previous iterations of hoisting.

llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp

for (const HoistingPointInfo &HP : HPL) {
             MemoryAccess *OldMA = MSSA->getMemoryAccess(I);
             OldMA->replaceAllUsesWith(NewMemAcc);
             MSSA->removeMemoryAccess(OldMA);
           }
 
           Repl->intersectOptionalDataWith(I);
           combineKnownMetadata(Repl, I);
           I->replaceAllUsesWith(Repl);
+          // Also invalidate the Alias Analysis cache.
+          MD->removeInstruction(I);
           I->eraseFromParent();
         }
 
       // Remove MemorySSA phi nodes with the same arguments.
       if (NewMemAcc) {
         SmallPtrSet<MemoryPhi *, 4> UsePhis;
         for (User *U : NewMemAcc->users())
           if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(U))