X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=utils%2FTableGen%2FDAGISelMatcherGen.cpp;h=d32d3a7b132d957322b98fa19d25c9091e66f611;hb=92d3ada814f33e3e1d10f0e5e3a15333b0cca849;hp=afa258718f1549a899290ce5533a58bd9fa52242;hpb=da272d1a704bd564272e88cbdbcf14712e3abbdc;p=oota-llvm.git

diff --git a/utils/TableGen/DAGISelMatcherGen.cpp b/utils/TableGen/DAGISelMatcherGen.cpp
index afa258718f1..d32d3a7b132 100644
--- a/utils/TableGen/DAGISelMatcherGen.cpp
+++ b/utils/TableGen/DAGISelMatcherGen.cpp
@@ -186,22 +186,57 @@ void MatcherGen::EmitOperatorMatchCode(const TreePatternNode *N,
   // If this node has a chain, then the chain is operand #0 is the SDNode, and
   // the child numbers of the node are all offset by one.
   unsigned OpNo = 0;
-  if (N->NodeHasProperty(SDNPHasChain, CGP))
+  if (N->NodeHasProperty(SDNPHasChain, CGP)) {
     OpNo = 1;
 
-  if (N->TreeHasProperty(SDNPHasChain, CGP)) {
-    // FIXME: Handle Chains with multiple uses etc.
-    //         [ld]
+    // If this node is not the root and the subtree underneath it produces a
+    // chain, then the result of matching the node is also produce a chain.
+    // Beyond that, this means that we're also folding (at least) the root node
+    // into the node that produce the chain (for example, matching
+    // "(add reg, (load ptr))" as a add_with_memory on X86).  This is
+    // problematic, if the 'reg' node also uses the load (say, its chain).
+    // Graphically:
+    //
+    //         [LD]
     //         ^  ^
-    //         |  |
-    //        /   \---
-    //      /        [YY]
-    //      |         ^
-    //     [XX]-------|
+    //         |  \                              DAG's like cheese.
+    //        /    |
+    //       /    [YY]
+    //       |     ^
+    //      [XX]--/
+    //
+    // It would be invalid to fold XX and LD.  In this case, folding the two
+    // nodes together would induce a cycle in the DAG, making it a 'cyclic DAG'
+    // To prevent this, we emit a dynamic check for legality before allowing
+    // this to be folded.
+    //
+    const TreePatternNode *Root = Pattern.getSrcPattern();
+    if (N != Root) {                             // Not the root of the pattern.
+      // If there is a node between the root and this node, then we definitely
+      // need to emit the check.
+      bool NeedCheck = !Root->hasChild(N);
+      
+      // If it *is* an immediate child of the root, we can still need a check if
+      // the root SDNode has multiple inputs.  For us, this means that it is an
+      // intrinsic, has multiple operands, or has other inputs like chain or
+      // flag).
+      if (!NeedCheck) {
+        const SDNodeInfo &PInfo = CGP.getSDNodeInfo(Root->getOperator());
+        NeedCheck =
+          Root->getOperator() == CGP.get_intrinsic_void_sdnode() ||
+          Root->getOperator() == CGP.get_intrinsic_w_chain_sdnode() ||
+          Root->getOperator() == CGP.get_intrinsic_wo_chain_sdnode() ||
+          PInfo.getNumOperands() > 1 ||
+          PInfo.hasProperty(SDNPHasChain) ||
+          PInfo.hasProperty(SDNPInFlag) ||
+          PInfo.hasProperty(SDNPOptInFlag);
+      }
+      
+      if (NeedCheck)
+        AddMatcherNode(new CheckFoldableChainNodeMatcherNode());
+    }
   }
       
-  // FIXME: Handle Flags & .hasOneUse()
-  
   for (unsigned i = 0, e = N->getNumChildren(); i != e; ++i, ++OpNo) {
     // Get the code suitable for matching this child.  Move to the child, check
     // it then move back to the parent.