Fix some faulty logic in the libcall inserter.

Since calls return more than one value, don't bail if one of their uses
happens to be a node that's not an MVT::Other when following the chain
from CALLSEQ_START to CALLSEQ_END.

Once we've found a CALLSEQ_START, we can just return; there's no need to
tail-recurse further up the graph.

Most importantly, just because something only has one use doesn't mean we
should use it's one use to follow from start to end.  This faulty logic
caused us to follow a chain of one-use FP operations back to a much earlier
call, putting a cycle in the graph from a later start to an earlier end.

This is a better fix that reverting to the workaround committed earlier
today.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23620 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 19 deletions

diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 2250c7f431..17ea3edf20 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -623,20 +623,9 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
     Tmp1 = LegalizeOp(Node->getOperand(0));  // Legalize the chain.
     // Do not try to legalize the target-specific arguments (#1+)
     Tmp2 = Node->getOperand(0);
-    if (Tmp1 != Tmp2) {
+    if (Tmp1 != Tmp2)
       Node->setAdjCallChain(Tmp1);
       
-      // If moving the operand from pointing to Tmp2 dropped its use count to 1,
-      // this will cause the maps used to memoize results to get confused.
-      // Create and add a dummy use, just to increase its use count.  This will
-      // be removed at the end of legalize when dead nodes are removed.
-      if (Tmp2.Val->hasOneUse()) {
-        // FIXME: find out why this code is necessary
-        DAG.getNode(ISD::PCMARKER, MVT::Other, Tmp2, 
-                    DAG.getConstant(0, MVT::i32));
-      }
-    }
-      
     // Note that we do not create new CALLSEQ_DOWN/UP nodes here.  These
     // nodes are treated specially and are mutated in place.  This makes the dag
     // legalization process more efficient and also makes libcall insertion
@@ -2630,8 +2619,11 @@ static void FindLatestCallSeqStart(SDNode *Node, SDNode *&Found) {
   // Otherwise, scan the operands of Node to see if any of them is a call.
   assert(Node->getNumOperands() != 0 &&
          "All leaves should have depth equal to the entry node!");
-  for (unsigned i = 0, e = Node->getNumOperands()-1; i != e; ++i)
+  for (unsigned i = 0, e = Node->getNumOperands()-1; i != e; ++i) {
     FindLatestCallSeqStart(Node->getOperand(i).Val, Found);
+    if (Found->getOpcode() == ISD::CALLSEQ_START)
+      return;
+  }
 
   // Tail recurse for the last iteration.
   FindLatestCallSeqStart(Node->getOperand(Node->getNumOperands()-1).Val,
@@ -2672,13 +2664,11 @@ static SDNode *FindCallSeqEnd(SDNode *Node) {
   if (Node->use_empty())
     return 0;   // No CallSeqEnd
 
-  if (Node->hasOneUse())  // Simple case, only has one user to check.
-    return FindCallSeqEnd(*Node->use_begin());
-
   SDOperand TheChain(Node, Node->getNumValues()-1);
   if (TheChain.getValueType() != MVT::Other)
     TheChain = SDOperand(Node, 0);
-  assert(TheChain.getValueType() == MVT::Other && "Is not a token chain!");
+  if (TheChain.getValueType() != MVT::Other)
+    return 0;
 
   for (SDNode::use_iterator UI = Node->use_begin(),
          E = Node->use_end(); UI != E; ++UI) {
@@ -2722,10 +2712,12 @@ static SDOperand FindInputOutputChains(SDNode *OpNode, SDNode *&OutChain,
   // previous call in the function.  LatestCallStackDown may in that case be
   // the entry node itself.  Do not attempt to find a matching CALLSEQ_END
   // unless LatestCallStackDown is an CALLSEQ_START.
-  if (LatestCallSeqStart->getOpcode() == ISD::CALLSEQ_START)
+  if (LatestCallSeqStart->getOpcode() == ISD::CALLSEQ_START) {
     LatestCallSeqEnd = FindCallSeqEnd(LatestCallSeqStart);
-  else
+    //std::cerr<<"Found end node: "; LatestCallSeqEnd->dump(); std::cerr <<"\n";
+  } else {
     LatestCallSeqEnd = Entry.Val;
+  }
   assert(LatestCallSeqEnd && "NULL return from FindCallSeqEnd");
 
   // Finally, find the first call that this must come before, first we find the