Fix bug: Dominators/2003-05-12-UnreachableCode.ll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6158 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/VMCore/Dominators.cpp b/lib/VMCore/Dominators.cpp
index a9479aa635517de8430e993069b530152d4ffe4b..be9984bb122bcca5963b9dc355cded2127f47dab 100644 (file)
--- a/lib/VMCore/Dominators.cpp
+++ b/lib/VMCore/Dominators.cpp
@@ -51,16 +51,25 @@ void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
       if (PI != PEnd) {                // Is there SOME predecessor?
        // Loop until we get to a predecessor that has had it's dom set filled
        // in at least once.  We are guaranteed to have this because we are
-       // traversing the graph in DFO and have handled start nodes specially.
+       // traversing the graph in DFO and have handled start nodes specially,
+       // except when there are unreachable blocks.
        //
-       while (Doms[*PI].empty()) ++PI;
-       WorkingSet = Doms[*PI];
-
-       for (++PI; PI != PEnd; ++PI) { // Intersect all of the predecessor sets
-         DomSetType &PredSet = Doms[*PI];
-         if (PredSet.size())
-           set_intersect(WorkingSet, PredSet);
-       }
+       while (PI != PEnd && Doms[*PI].empty()) ++PI;
+        if (PI != PEnd) {     // Not unreachable code case?
+          WorkingSet = Doms[*PI];
+
+          // Intersect all of the predecessor sets
+          for (++PI; PI != PEnd; ++PI) {
+            DomSetType &PredSet = Doms[*PI];
+            if (PredSet.size())
+              set_intersect(WorkingSet, PredSet);
+          }
+        } else {
+          // Otherwise this block is unreachable.  it doesn't really matter what
+          // we use for the dominator set for the node...
+          //
+          WorkingSet = Doms[Root];
+        }
       } else if (BB != Root) {
         // If this isn't the root basic block and it has no predecessors, it
         // must be an unreachable block.  Fib a bit by saying that the root node