IR: Fix BasicBlock::phis for empty blocks

[arsenm]

ping

[• dberlin]

lib/IR/BasicBlock.cpp

267

I would just use

// PHINodes, if they exist, come first in the block
PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin())

[davide]

Can you add a unittest to show this issue?

[arsenm]

r321567

lib/IR/BasicBlock.cpp

if (*SI != SuccBB)
       return nullptr;
     // The same successor appears multiple times in the successor list.
     // This is OK.
   }
   return SuccBB;
 }
 
 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
-  return make_range<phi_iterator>(dyn_cast<PHINode>(&front()), nullptr);
+  PHINode *P = nullptr;
+  auto I = begin();
+  if (I != end())
+    P = dyn_cast<PHINode>(&*I);
+
+  return make_range<phi_iterator>(P, nullptr);
 }
 
 /// This method is used to notify a BasicBlock that the
 /// specified Predecessor of the block is no longer able to reach it.  This is
 /// actually not used to update the Predecessor list, but is actually used to
 /// update the PHI nodes that reside in the block.  Note that this should be
 /// called while the predecessor still refers to this block.
 ///