Avoid exponential blow-up when printing DAGs.

David Greene changed CannotYetSelect() to print the full DAG including multiple
copies of operands reached through different paths in the DAG.  Unfortunately
this blows up exponentially in some cases.  The depth limit of 100 is way too
high to prevent this -- I'm seeing a message string of 150MB with a depth of
only 40 in one particularly bad case, even though the DAG has less than 200
nodes.  Part of the problem is that the printing code is following chain
operands, so if you fail to select an operation with a chain, the printer will
follow all the chained operations back to the entry node.

llvm-svn: 126899

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9120288921e..6a8c92e64ec 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6226,6 +6226,9 @@ static void printrWithDepthHelper(raw_ostream &OS, const SDNode *N,
     return;
 
   for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    // Don't follow chain operands.
+    if (N->getOperand(i).getValueType() == MVT::Other)
+      continue;
     OS << '\n';
     printrWithDepthHelper(OS, N->getOperand(i).getNode(), G, depth-1, indent+2);
   }
@@ -6238,7 +6241,7 @@ void SDNode::printrWithDepth(raw_ostream &OS, const SelectionDAG *G,
 
 void SDNode::printrFull(raw_ostream &OS, const SelectionDAG *G) const {
   // Don't print impossibly deep things.
-  printrWithDepth(OS, G, 100);
+  printrWithDepth(OS, G, 10);
 }
 
 void SDNode::dumprWithDepth(const SelectionDAG *G, unsigned depth) const {
@@ -6247,7 +6250,7 @@ void SDNode::dumprWithDepth(const SelectionDAG *G, unsigned depth) const {
 
 void SDNode::dumprFull(const SelectionDAG *G) const {
   // Don't print impossibly deep things.
-  dumprWithDepth(G, 100);
+  dumprWithDepth(G, 10);
 }
 
 static void DumpNodes(const SDNode *N, unsigned indent, const SelectionDAG *G) {