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

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/VMCore/Dominators.cpp b/lib/VMCore/Dominators.cpp
index 60bdeac16b..77b2403d87 100644
--- a/lib/VMCore/Dominators.cpp
+++ b/lib/VMCore/Dominators.cpp
@@ -161,6 +161,11 @@ bool DominatorTree::dominates(const Instruction *Def,
 
 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
                               const BasicBlock *UseBB) const {
+  // Assert that we have a single edge. We could handle them by simply
+  // returning false, but since isSingleEdge is linear on the number of
+  // edges, the callers can normally handle them more efficiently.
+  assert(BBE.isSingleEdge());
+
   // If the BB the edge ends in doesn't dominate the use BB, then the
   // edge also doesn't.
   const BasicBlock *Start = BBE.getStart();
@@ -207,6 +212,11 @@ bool DominatorTree::dominates(const BasicBlockEdge &BBE,
 
 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
                               const Use &U) const {
+  // Assert that we have a single edge. We could handle them by simply
+  // returning false, but since isSingleEdge is linear on the number of
+  // edges, the callers can normally handle them more efficiently.
+  assert(BBE.isSingleEdge());
+
   Instruction *UserInst = cast<Instruction>(U.getUser());
   // A PHI in the end of the edge is dominated by it.
   PHINode *PN = dyn_cast<PHINode>(UserInst);