Assert that dominates is not given a multiple edge. Finding out if we have

multiple edges between two blocks is linear. If the caller is iterating all
edges leaving a BB that would be a square time algorithm. It is more efficient
to have the callers handle that case.

Currently the only callers are:
* GVN: already avoids the multiple edge case.
* Verifier: could only hit this assert when looking at an invalid invoke. Since
it already rejects the invoke, just avoid computing the dominance for it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162113 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/Verifier.cpp

@@ -1575,6 +1575,13 @@ void Verifier::visitLandingPadInst(LandingPadInst &LPI) {
 
 void Verifier::verifyDominatesUse(Instruction &I, unsigned i) {
   Instruction *Op = cast<Instruction>(I.getOperand(i));
+  // If the we have an invalid invoke, don't try to compute the dominance.
+  // We already reject it in the invoke specific checks and the dominance
+  // computation doesn't handle multiple edges.
+  if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
+    if (II->getNormalDest() == II->getUnwindDest())
+      return;
+  }
 
   const Use &U = I.getOperandUse(i);
   Assert2(InstsInThisBlock.count(Op) || DT->dominates(Op, U),