[llvm-commits] [llvm] r134428 - /llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Tue Jul  5 13:46:42 2011
New Revision: 134428

URL: http://llvm.org/viewvc/llvm-project?rev=134428&view=rev
Log:
Break infinite loop when the Hopfield network oscillates.

This is impossible in theory, I can prove it. In practice, our near-zero
threshold can cause the network to oscillate between equally good
solutions.

<rdar://problem/9720596>

Modified:
    llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp

Modified: llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp?rev=134428&r1=134427&r2=134428&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp Tue Jul  5 13:46:42 2011
@@ -649,8 +649,6 @@
 
   for (;;) {
     ArrayRef<unsigned> NewBundles = SpillPlacer->getRecentPositive();
-    if (NewBundles.empty())
-      break;
     // Find new through blocks in the periphery of PrefRegBundles.
     for (int i = 0, e = NewBundles.size(); i != e; ++i) {
       unsigned Bundle = NewBundles[i];
@@ -670,12 +668,12 @@
       }
     }
     // Any new blocks to add?
-    if (ActiveBlocks.size() > AddedTo) {
-      ArrayRef<unsigned> Add(&ActiveBlocks[AddedTo],
-                             ActiveBlocks.size() - AddedTo);
-      addThroughConstraints(Intf, Add);
-      AddedTo = ActiveBlocks.size();
-    }
+    if (ActiveBlocks.size() == AddedTo)
+      break;
+    addThroughConstraints(Intf,
+                          ArrayRef<unsigned>(ActiveBlocks).slice(AddedTo));
+    AddedTo = ActiveBlocks.size();
+
     // Perhaps iterating can enable more bundles?
     SpillPlacer->iterate();
   }