Fix a nasty problem with dominance calculation for unreachable blocks.

If we had a CFG that look like Entry -> B, Unreachable -> B, then we would
not correctly determine that Entry dominated B, because Entry did not
apparently dominate "unreachable".  This patch fixes this by making the entry
node dominate all blocks, including unreachable ones.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4037 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 20 insertions, 5 deletions

diff --git a/lib/VMCore/Dominators.cpp b/lib/VMCore/Dominators.cpp
index 99fda80751..37e7d48c28 100644
--- a/lib/VMCore/Dominators.cpp
+++ b/lib/VMCore/Dominators.cpp
@@ -61,6 +61,18 @@ void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
 	  if (PredSet.size())
 	    set_intersect(WorkingSet, PredSet);
 	}
+      } 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
+        // dominates this unreachable node.  This isn't exactly true, because
+        // there is no path from the entry node to this node, but it is sorta
+        // true because any paths to this node would have to go through the
+        // entry node.
+        //
+        // This allows for dominator properties to be built for unreachable code
+        // in a reasonable manner.
+        //
+        WorkingSet = Doms[Root];
       }
 	
       WorkingSet.insert(BB);           // A block always dominates itself
@@ -95,9 +107,8 @@ bool DominatorSet::runOnFunction(Function &F) {
   // unreachable blocks.
   //
   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-    if (Doms[I].empty()) {
+    if (Doms[I].count(I) == 0)
       calculateDominatorsFromBlock(I);
-    }
 
   return false;
 }
@@ -166,10 +177,14 @@ void ImmediateDominatorsBase::calcIDoms(const DominatorSetBase &DS) {
 }
 
 void ImmediateDominatorsBase::print(std::ostream &o) const {
-  for (const_iterator I = begin(), E = end(); I != E; ++I)
+  for (const_iterator I = begin(), E = end(); I != E; ++I) {
     o << "=============================--------------------------------\n"
-      << "\nImmediate Dominator For Basic Block\n" << *I->first
-      << "is: \n" << *I->second << "\n";
+      << "\nImmediate Dominator For Basic Block:";
+    WriteAsOperand(o, I->first, false);
+    o << " is:";
+    WriteAsOperand(o, I->second, false);
+    o << "\n";
+  }
 }