Subzero: Prune unreachable nodes after constructing the Cfg.

src/IceCfg.cpp

 //===- subzero/src/IceCfg.cpp - Control flow graph implementation ---------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the Cfg class, including constant pool
@@ skipping 90 matching lines @@
 
   // The set of translation passes and their order are determined by
   // the target.
   getTarget()->translate();
 
   dump("Final output");
   if (getFocusedTiming())
     getContext()->dumpTimers();
 }
 
-void Cfg::computePredecessors() {
+void Cfg::computeInOutEdges() {
+  // Compute the out-edges.
   for (CfgNode *Node : Nodes)
-    Node->computePredecessors();
+    Node->computeSuccessors();
+
+  // Prune any unreachable nodes before computing in-edges.
+  SizeT NumNodes = getNumNodes();
+  llvm::BitVector Reachable(NumNodes);
+  llvm::BitVector Pending(NumNodes);
+  Pending.set(getEntryNode()->getIndex());
+  while (true) {
+    int Index = Pending.find_first();
+    if (Index == -1)
+      break;
+    Pending.reset(Index);
+    Reachable.set(Index);
+    CfgNode *Node = Nodes[Index];
+    assert(Node->getIndex() == (SizeT)Index);
+    for (CfgNode *Succ : Node->getOutEdges()) {
+      SizeT SuccIndex = Succ->getIndex();
+      if (!Reachable.test(SuccIndex))
+        Pending.set(SuccIndex);
+    }
+  }
+  SizeT Dest = 0;
+  for (SizeT Source = 0; Source < NumNodes; ++Source) {
+    if (Reachable.test(Source)) {
+      Nodes[Dest] = Nodes[Source];
+      Nodes[Dest]->resetIndex(Dest);
+      // Compute the in-edges.
+      Nodes[Dest]->computePredecessors();
+      ++Dest;
+    }
+  }
+  Nodes.resize(Dest);
 }
 
 void Cfg::renumberInstructions() {
   TimerMarker T(TimerStack::TT_renumberInstructions, this);
   NextInstNumber = Inst::NumberInitial;
   for (CfgNode *Node : Nodes)
     Node->renumberInstructions();
 }
 
 // placePhiLoads() must be called before placePhiStores().
@@ skipping 385 matching lines @@
     }
   }
   // Print each basic block
   for (CfgNode *Node : Nodes)
     Node->dump(this);
   if (isVerbose(IceV_Instructions))
     Str << "}\n";
 }
 
 } // end of namespace Ice