[llvm-commits] [llvm] r83824 - /llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Nate Begeman]

Author: sampo
Date: Mon Oct 12 00:53:58 2009
New Revision: 83824

URL: http://llvm.org/viewvc/llvm-project?rev=83824&view=rev
Log:
More heuristics for Combiner-AA.  Still catches all important cases, but
compile time penalty on gnugo, the worst case in MultiSource, is down to
about 2.5% from 30%

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=83824&r1=83823&r2=83824&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Oct 12 00:53:58 2009
@@ -6230,13 +6230,28 @@
 
   // Starting off.
   Chains.push_back(OriginalChain);
-
+  unsigned Depth = 0;
+  
   // Look at each chain and determine if it is an alias.  If so, add it to the
   // aliases list.  If not, then continue up the chain looking for the next
   // candidate.
   while (!Chains.empty()) {
     SDValue Chain = Chains.back();
     Chains.pop_back();
+    
+    // For TokenFactor nodes, look at each operand and only continue up the 
+    // chain until we find two aliases.  If we've seen two aliases, assume we'll 
+    // find more and revert to original chain since the xform is unlikely to be
+    // profitable.
+    // 
+    // FIXME: The depth check could be made to return the last non-aliasing 
+    // chain we found before we hit a tokenfactor rather than the original
+    // chain.
+    if (Depth > 6 || Aliases.size() == 2) {
+      Aliases.clear();
+      Aliases.push_back(OriginalChain);
+      break;
+    }
 
     // Don't bother if we've been before.
     if (!Visited.insert(Chain.getNode()))
@@ -6268,8 +6283,7 @@
       } else {
         // Look further up the chain.
         Chains.push_back(Chain.getOperand(0));
-        // Clean up old chain.
-        AddToWorkList(Chain.getNode());
+        ++Depth;
       }
       break;
     }
@@ -6285,8 +6299,7 @@
       }
       for (unsigned n = Chain.getNumOperands(); n;)
         Chains.push_back(Chain.getOperand(--n));
-      // Eliminate the token factor if we can.
-      AddToWorkList(Chain.getNode());
+      ++Depth;
       break;
 
     default:
@@ -6312,7 +6325,7 @@
     // If a single operand then chain to it.  We don't need to revisit it.
     return Aliases[0];
   }
-
+  
   // Construct a custom tailored token factor.
   return DAG.getNode(ISD::TokenFactor, N->getDebugLoc(), MVT::Other, 
                      &Aliases[0], Aliases.size());