1 files changed, 199 insertions, 0 deletions
diff --git a/lib/CodeGen/UnreachableBlockElim.cpp b/lib/CodeGen/UnreachableBlockElim.cpp
new file mode 100644
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+++ b/lib/CodeGen/UnreachableBlockElim.cpp
@@ -0,0 +1,199 @@
+//===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is an extremely simple version of the SimplifyCFG pass.  Its sole
+// job is to delete LLVM basic blocks that are not reachable from the entry
+// node.  To do this, it performs a simple depth first traversal of the CFG,
+// then deletes any unvisited nodes.
+//
+// Note that this pass is really a hack.  In particular, the instruction
+// selectors for various targets should just not generate code for unreachable
+// blocks.  Until LLVM has a more systematic way of defining instruction
+// selectors, however, we cannot really expect them to handle additional
+// complexity.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Constant.h"
+#include "llvm/Instructions.h"
+#include "llvm/Function.h"
+#include "llvm/Pass.h"
+#include "llvm/Type.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+using namespace llvm;
+
+namespace {
+  class VISIBILITY_HIDDEN UnreachableBlockElim : public FunctionPass {
+    virtual bool runOnFunction(Function &F);
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    UnreachableBlockElim() : FunctionPass(&ID) {}
+  };
+}
+char UnreachableBlockElim::ID = 0;
+static RegisterPass<UnreachableBlockElim>
+X("unreachableblockelim", "Remove unreachable blocks from the CFG");
+
+FunctionPass *llvm::createUnreachableBlockEliminationPass() {
+  return new UnreachableBlockElim();
+}
+
+bool UnreachableBlockElim::runOnFunction(Function &F) {
+  SmallPtrSet<BasicBlock*, 8> Reachable;
+
+  // Mark all reachable blocks.
+  for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > I =
+       df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); I != E; ++I)
+    /* Mark all reachable blocks */;
+
+  // Loop over all dead blocks, remembering them and deleting all instructions
+  // in them.
+  std::vector<BasicBlock*> DeadBlocks;
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
+    if (!Reachable.count(I)) {
+      BasicBlock *BB = I;
+      DeadBlocks.push_back(BB);
+      while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+        PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
+        BB->getInstList().pop_front();
+      }
+      for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
+        (*SI)->removePredecessor(BB);
+      BB->dropAllReferences();
+    }
+
+  // Actually remove the blocks now.
+  for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
+    DeadBlocks[i]->eraseFromParent();
+
+  return DeadBlocks.size();
+}
+
+
+namespace {
+  class VISIBILITY_HIDDEN UnreachableMachineBlockElim :
+        public MachineFunctionPass {
+    virtual bool runOnMachineFunction(MachineFunction &F);
+    MachineModuleInfo *MMI;
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    UnreachableMachineBlockElim() : MachineFunctionPass(&ID) {}
+  };
+}
+char UnreachableMachineBlockElim::ID = 0;
+
+static RegisterPass<UnreachableMachineBlockElim>
+Y("unreachable-mbb-elimination",
+  "Remove unreachable machine basic blocks");
+
+const PassInfo *const llvm::UnreachableMachineBlockElimID = &Y;
+
+bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
+  SmallPtrSet<MachineBasicBlock*, 8> Reachable;
+
+  MMI = getAnalysisIfAvailable<MachineModuleInfo>();
+
+  // Mark all reachable blocks.
+  for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
+       I = df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable);
+       I != E; ++I)
+    /* Mark all reachable blocks */;
+
+  // Loop over all dead blocks, remembering them and deleting all instructions
+  // in them.
+  std::vector<MachineBasicBlock*> DeadBlocks;
+  for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    MachineBasicBlock *BB = I;
+
+    // Test for deadness.
+    if (!Reachable.count(BB)) {
+      DeadBlocks.push_back(BB);
+
+      while (BB->succ_begin() != BB->succ_end()) {
+        MachineBasicBlock* succ = *BB->succ_begin();
+
+        MachineBasicBlock::iterator start = succ->begin();
+        while (start != succ->end() &&
+               start->getOpcode() == TargetInstrInfo::PHI) {
+          for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
+            if (start->getOperand(i).isMBB() &&
+                start->getOperand(i).getMBB() == BB) {
+              start->RemoveOperand(i);
+              start->RemoveOperand(i-1);
+            }
+
+          start++;
+        }
+
+        BB->removeSuccessor(BB->succ_begin());
+      }
+    }
+  }
+
+  // Actually remove the blocks now.
+  for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
+    MachineBasicBlock *MBB = DeadBlocks[i];
+    // If there are any labels in the basic block, unregister them from
+    // MachineModuleInfo.
+    if (MMI && !MBB->empty()) {
+      for (MachineBasicBlock::iterator I = MBB->begin(),
+             E = MBB->end(); I != E; ++I) {
+        if (I->isLabel())
+          // The label ID # is always operand #0, an immediate.
+          MMI->InvalidateLabel(I->getOperand(0).getImm());
+      }
+    }
+    MBB->eraseFromParent();
+  }
+
+  // Cleanup PHI nodes.
+  for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    MachineBasicBlock *BB = I;
+    // Prune unneeded PHI entries.
+    SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
+                                             BB->pred_end());
+    MachineBasicBlock::iterator phi = BB->begin();
+    while (phi != BB->end() &&
+           phi->getOpcode() == TargetInstrInfo::PHI) {
+      for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
+        if (!preds.count(phi->getOperand(i).getMBB())) {
+          phi->RemoveOperand(i);
+          phi->RemoveOperand(i-1);
+        }
+
+      if (phi->getNumOperands() == 3) {
+        unsigned Input = phi->getOperand(1).getReg();
+        unsigned Output = phi->getOperand(0).getReg();
+
+        MachineInstr* temp = phi;
+        ++phi;
+        temp->eraseFromParent();
+
+        if (Input != Output)
+          F.getRegInfo().replaceRegWith(Output, Input);
+
+        continue;
+      }
+
+      ++phi;
+    }
+  }
+
+  F.RenumberBlocks();
+
+  return DeadBlocks.size();
+}