Relax an invariant that block placement was trying to assert a bit

[oota-llvm.git] / lib / CodeGen / MachineBlockPlacement.cpp

diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index 4cbc94e0b7dbbfb0d98a16bee5d266774fe23893..45d5af293039c941d408dbd7793902003213d8f6 100644 (file)
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -488,7 +488,10 @@ MachineBasicBlock *MachineBlockPlacement::getFirstUnplacedBlock(
       continue;
     if (BlockToChain[I] != &PlacedChain) {
       PrevUnplacedBlockIt = I;
-      return I;
+      // Now select the head of the chain to which the unplaced block belongs
+      // as the block to place. This will force the entire chain to be placed,
+      // and satisfies the requirements of merging chains.
+      return *BlockToChain[I]->begin();
     }
   }
   return 0;
@@ -501,7 +504,6 @@ void MachineBlockPlacement::buildChain(
     const BlockFilterSet *BlockFilter) {
   assert(BB);
   assert(BlockToChain[BB] == &Chain);
-  assert(*Chain.begin() == BB);
   MachineFunction &F = *BB->getParent();
   MachineFunction::iterator PrevUnplacedBlockIt = F.begin();
 
@@ -611,8 +613,7 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F,
       if (!LoopBlockSet.erase(*BCI)) {
         // We don't mark the loop as bad here because there are real situations
         // where this can occur. For example, with an unanalyzable fallthrough
-        // from a loop block to a non-loop block.
-        // FIXME: Such constructs shouldn't exist. Track them down and fix them.
+        // from a loop block to a non-loop block or vice versa.
         dbgs() << "Loop chain contains a block not contained by the loop!\n"
                << "  Loop header:  " << getBlockName(*L.block_begin()) << "\n"
                << "  Chain header: " << getBlockName(*LoopChain.begin()) << "\n"