[IR] Reformulate LLVM's EH funclet IR

While we have successfully implemented a funclet-oriented EH scheme on
top of LLVM IR, our scheme has some notable deficiencies:
- catchendpad and cleanupendpad are necessary in the current design
  but they are difficult to explain to others, even to seasoned LLVM
  experts.
- catchendpad and cleanupendpad are optimization barriers.  They cannot
  be split and force all potentially throwing call-sites to be invokes.
  This has a noticable effect on the quality of our code generation.
- catchpad, while similar in some aspects to invoke, is fairly awkward.
  It is unsplittable, starts a funclet, and has control flow to other
  funclets.
- The nesting relationship between funclets is currently a property of
  control flow edges.  Because of this, we are forced to carefully
  analyze the flow graph to see if there might potentially exist illegal
  nesting among funclets.  While we have logic to clone funclets when
  they are illegally nested, it would be nicer if we had a
  representation which forbade them upfront.

Let's clean this up a bit by doing the following:
- Instead, make catchpad more like cleanuppad and landingpad: no control
  flow, just a bunch of simple operands;  catchpad would be splittable.
- Introduce catchswitch, a control flow instruction designed to model
  the constraints of funclet oriented EH.
- Make funclet scoping explicit by having funclet instructions consume
  the token produced by the funclet which contains them.
- Remove catchendpad and cleanupendpad.  Their presence can be inferred
  implicitly using coloring information.

N.B.  The state numbering code for the CLR has been updated but the
veracity of it's output cannot be spoken for.  An expert should take a
look to make sure the results are reasonable.

Reviewers: rnk, JosephTremoulet, andrew.w.kaylor

Differential Revision: http://reviews.llvm.org/D15139

llvm-svn: 255422

9 files changed, 148 insertions, 79 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 218e3e96c23..91bb3337509 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -2684,12 +2684,12 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     setOrigin(&I, getCleanOrigin());
   }
 
-  void visitCleanupPadInst(CleanupPadInst &I) {
+  void visitCatchSwitchInst(CatchSwitchInst &I) {
     setShadow(&I, getCleanShadow(&I));
     setOrigin(&I, getCleanOrigin());
   }
 
-  void visitCatchPad(CatchPadInst &I) {
+  void visitFuncletPadInst(FuncletPadInst &I) {
     setShadow(&I, getCleanShadow(&I));
     setOrigin(&I, getCleanOrigin());
   }
@@ -2699,16 +2699,6 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     // Nothing to do here.
   }
 
-  void visitCatchEndPadInst(CatchEndPadInst &I) {
-    DEBUG(dbgs() << "CatchEndPad: " << I << "\n");
-    // Nothing to do here.
-  }
-
-  void visitCleanupEndPadInst(CleanupEndPadInst &I) {
-    DEBUG(dbgs() << "CleanupEndPad: " << I << "\n");
-    // Nothing to do here.
-  }
-
   void visitGetElementPtrInst(GetElementPtrInst &I) {
     handleShadowOr(I);
   }
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index fa2f7d995c6..13d9b6d4fee 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -947,8 +947,6 @@ static Value *NegateValue(Value *V, Instruction *BI,
     if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
       if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
         InsertPt = II->getNormalDest()->begin();
-      } else if (auto *CPI = dyn_cast<CatchPadInst>(InstInput)) {
-        InsertPt = CPI->getNormalDest()->begin();
       } else {
         InsertPt = ++InstInput->getIterator();
       }
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 52281d4e044..2fca803adde 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -480,8 +480,10 @@ private:
   void visitExtractValueInst(ExtractValueInst &EVI);
   void visitInsertValueInst(InsertValueInst &IVI);
   void visitLandingPadInst(LandingPadInst &I) { markAnythingOverdefined(&I); }
-  void visitCleanupPadInst(CleanupPadInst &CPI) { markAnythingOverdefined(&CPI); }
-  void visitCatchPadInst(CatchPadInst &CPI) {
+  void visitFuncletPadInst(FuncletPadInst &FPI) {
+    markAnythingOverdefined(&FPI);
+  }
+  void visitCatchSwitchInst(CatchSwitchInst &CPI) {
     markAnythingOverdefined(&CPI);
     visitTerminatorInst(CPI);
   }
diff --git a/llvm/lib/Transforms/Scalar/Sink.cpp b/llvm/lib/Transforms/Scalar/Sink.cpp
index 7c0ac7aa6fa..64109b2df11 100644
--- a/llvm/lib/Transforms/Scalar/Sink.cpp
+++ b/llvm/lib/Transforms/Scalar/Sink.cpp
@@ -169,7 +169,8 @@ static bool isSafeToMove(Instruction *Inst, AliasAnalysis *AA,
         return false;
   }
 
-  if (isa<TerminatorInst>(Inst) || isa<PHINode>(Inst) || Inst->isEHPad())
+  if (isa<TerminatorInst>(Inst) || isa<PHINode>(Inst) || Inst->isEHPad() ||
+      Inst->mayThrow())
     return false;
 
   // Convergent operations cannot be made control-dependent on additional
@@ -194,6 +195,11 @@ bool Sinking::IsAcceptableTarget(Instruction *Inst,
   if (Inst->getParent() == SuccToSinkTo)
     return false;
 
+  // It's never legal to sink an instruction into a block which terminates in an
+  // EH-pad.
+  if (SuccToSinkTo->getTerminator()->isExceptional())
+    return false;
+
   // If the block has multiple predecessors, this would introduce computation
   // on different code paths.  We could split the critical edge, but for now we
   // just punt.
diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index 8ee596e5323..823696d88e6 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -560,8 +560,8 @@ emitCallAndSwitchStatement(Function *newFunction, BasicBlock *codeReplacer,
           // Restore values just before we exit
           Function::arg_iterator OAI = OutputArgBegin;
           for (unsigned out = 0, e = outputs.size(); out != e; ++out) {
-            // For an invoke/catchpad, the normal destination is the only one
-            // that is dominated by the result of the invocation
+            // For an invoke, the normal destination is the only one that is
+            // dominated by the result of the invocation
             BasicBlock *DefBlock = cast<Instruction>(outputs[out])->getParent();
 
             bool DominatesDef = true;
@@ -569,8 +569,6 @@ emitCallAndSwitchStatement(Function *newFunction, BasicBlock *codeReplacer,
             BasicBlock *NormalDest = nullptr;
             if (auto *Invoke = dyn_cast<InvokeInst>(outputs[out]))
               NormalDest = Invoke->getNormalDest();
-            if (auto *CatchPad = dyn_cast<CatchPadInst>(outputs[out]))
-              NormalDest = CatchPad->getNormalDest();
 
             if (NormalDest) {
               DefBlock = NormalDest;
diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index cafd1818fed..74ece385581 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Attributes.h"
@@ -192,8 +193,6 @@ HandleCallsInBlockInlinedThroughInvoke(BasicBlock *BB, BasicBlock *UnwindEdge) {
     // instructions require no special handling.
     CallInst *CI = dyn_cast<CallInst>(I);
 
-    // If this call cannot unwind, don't convert it to an invoke.
-    // Inline asm calls cannot throw.
     if (!CI || CI->doesNotThrow() || isa<InlineAsm>(CI->getCalledValue()))
       continue;
 
@@ -327,40 +326,10 @@ static void HandleInlinedEHPad(InvokeInst *II, BasicBlock *FirstNewBlock,
     }
   };
 
-  // Forward EH terminator instructions to the caller's invoke destination.
-  // This is as simple as connect all the instructions which 'unwind to caller'
-  // to the invoke destination.
+  // This connects all the instructions which 'unwind to caller' to the invoke
+  // destination.
   for (Function::iterator BB = FirstNewBlock->getIterator(), E = Caller->end();
        BB != E; ++BB) {
-    Instruction *I = BB->getFirstNonPHI();
-    if (I->isEHPad()) {
-      if (auto *CEPI = dyn_cast<CatchEndPadInst>(I)) {
-        if (CEPI->unwindsToCaller()) {
-          CatchEndPadInst::Create(CEPI->getContext(), UnwindDest, CEPI);
-          CEPI->eraseFromParent();
-          UpdatePHINodes(&*BB);
-        }
-      } else if (auto *CEPI = dyn_cast<CleanupEndPadInst>(I)) {
-        if (CEPI->unwindsToCaller()) {
-          CleanupEndPadInst::Create(CEPI->getCleanupPad(), UnwindDest, CEPI);
-          CEPI->eraseFromParent();
-          UpdatePHINodes(&*BB);
-        }
-      } else if (auto *TPI = dyn_cast<TerminatePadInst>(I)) {
-        if (TPI->unwindsToCaller()) {
-          SmallVector<Value *, 3> TerminatePadArgs;
-          for (Value *ArgOperand : TPI->arg_operands())
-            TerminatePadArgs.push_back(ArgOperand);
-          TerminatePadInst::Create(TPI->getContext(), UnwindDest,
-                                   TerminatePadArgs, TPI);
-          TPI->eraseFromParent();
-          UpdatePHINodes(&*BB);
-        }
-      } else {
-        assert(isa<CatchPadInst>(I) || isa<CleanupPadInst>(I));
-      }
-    }
-
     if (auto *CRI = dyn_cast<CleanupReturnInst>(BB->getTerminator())) {
       if (CRI->unwindsToCaller()) {
         CleanupReturnInst::Create(CRI->getCleanupPad(), UnwindDest, CRI);
@@ -368,6 +337,40 @@ static void HandleInlinedEHPad(InvokeInst *II, BasicBlock *FirstNewBlock,
         UpdatePHINodes(&*BB);
       }
     }
+
+    Instruction *I = BB->getFirstNonPHI();
+    if (!I->isEHPad())
+      continue;
+
+    Instruction *Replacement = nullptr;
+    if (auto *TPI = dyn_cast<TerminatePadInst>(I)) {
+      if (TPI->unwindsToCaller()) {
+        SmallVector<Value *, 3> TerminatePadArgs;
+        for (Value *ArgOperand : TPI->arg_operands())
+          TerminatePadArgs.push_back(ArgOperand);
+        Replacement = TerminatePadInst::Create(TPI->getParentPad(), UnwindDest,
+                                               TerminatePadArgs, TPI);
+      }
+    } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(I)) {
+      if (CatchSwitch->unwindsToCaller()) {
+        auto *NewCatchSwitch = CatchSwitchInst::Create(
+            CatchSwitch->getParentPad(), UnwindDest,
+            CatchSwitch->getNumHandlers(), CatchSwitch->getName(),
+            CatchSwitch);
+        for (BasicBlock *PadBB : CatchSwitch->handlers())
+          NewCatchSwitch->addHandler(PadBB);
+        Replacement = NewCatchSwitch;
+      }
+    } else if (!isa<FuncletPadInst>(I)) {
+      llvm_unreachable("unexpected EHPad!");
+    }
+
+    if (Replacement) {
+      Replacement->takeName(I);
+      I->replaceAllUsesWith(Replacement);
+      I->eraseFromParent();
+      UpdatePHINodes(&*BB);
+    }
   }
 
   if (InlinedCodeInfo.ContainsCalls)
@@ -1090,6 +1093,53 @@ bool llvm::InlineFunction(CallSite CS, InlineFunctionInfo &IFI,
       return false;
   }
 
+  // We need to figure out which funclet the callsite was in so that we may
+  // properly nest the callee.
+  Instruction *CallSiteEHPad = nullptr;
+  if (CalledPersonality && CallerPersonality) {
+    EHPersonality Personality = classifyEHPersonality(CalledPersonality);
+    if (isFuncletEHPersonality(Personality)) {
+      DenseMap<BasicBlock *, ColorVector> CallerBlockColors =
+          colorEHFunclets(*Caller);
+      ColorVector &CallSiteColors = CallerBlockColors[OrigBB];
+      size_t NumColors = CallSiteColors.size();
+      // There is no single parent, inlining will not succeed.
+      if (NumColors > 1)
+        return false;
+      if (NumColors == 1) {
+        BasicBlock *CallSiteFuncletBB = CallSiteColors.front();
+        if (CallSiteFuncletBB != Caller->begin()) {
+          CallSiteEHPad = CallSiteFuncletBB->getFirstNonPHI();
+          assert(CallSiteEHPad->isEHPad() && "Expected an EHPad!");
+        }
+      }
+
+      // OK, the inlining site is legal.  What about the target function?
+
+      if (CallSiteEHPad) {
+        if (Personality == EHPersonality::MSVC_CXX) {
+          // The MSVC personality cannot tolerate catches getting inlined into
+          // cleanup funclets.
+          if (isa<CleanupPadInst>(CallSiteEHPad)) {
+            // Ok, the call site is within a cleanuppad.  Let's check the callee
+            // for catchpads.
+            for (const BasicBlock &CalledBB : *CalledFunc) {
+              if (isa<CatchPadInst>(CalledBB.getFirstNonPHI()))
+                return false;
+            }
+          }
+        } else if (isAsynchronousEHPersonality(Personality)) {
+          // SEH is even less tolerant, there may not be any sort of exceptional
+          // funclet in the callee.
+          for (const BasicBlock &CalledBB : *CalledFunc) {
+            if (CalledBB.isEHPad())
+              return false;
+          }
+        }
+      }
+    }
+  }
+
   // Get an iterator to the last basic block in the function, which will have
   // the new function inlined after it.
   Function::iterator LastBlock = --Caller->end();
@@ -1381,6 +1431,30 @@ bool llvm::InlineFunction(CallSite CS, InlineFunctionInfo &IFI,
     }
   }
 
+  // Update the lexical scopes of the new funclets.  Anything that had 'none' as
+  // its parent is now nested inside the callsite's EHPad.
+  if (CallSiteEHPad) {
+    for (Function::iterator BB = FirstNewBlock->getIterator(),
+                            E = Caller->end();
+         BB != E; ++BB) {
+      Instruction *I = BB->getFirstNonPHI();
+      if (!I->isEHPad())
+        continue;
+
+      if (auto *TPI = dyn_cast<TerminatePadInst>(I)) {
+        if (isa<ConstantTokenNone>(TPI->getParentPad()))
+          TPI->setParentPad(CallSiteEHPad);
+      } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(I)) {
+        if (isa<ConstantTokenNone>(CatchSwitch->getParentPad()))
+          CatchSwitch->setParentPad(CallSiteEHPad);
+      } else {
+        auto *FPI = cast<FuncletPadInst>(I);
+        if (isa<ConstantTokenNone>(FPI->getParentPad()))
+          FPI->setParentPad(CallSiteEHPad);
+      }
+    }
+  }
+
   // If we are inlining for an invoke instruction, we must make sure to rewrite
   // any call instructions into invoke instructions.
   if (auto *II = dyn_cast<InvokeInst>(TheCall)) {
diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
index 12a8c71d829..ef2f5042169 100644
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -84,15 +84,13 @@ static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
 
   ++NumLCSSA; // We are applying the transformation
 
-  // Invoke/CatchPad instructions are special in that their result value is not
-  // available along their unwind edge. The code below tests to see whether
-  // DomBB dominates the value, so adjust DomBB to the normal destination block,
+  // Invoke instructions are special in that their result value is not available
+  // along their unwind edge. The code below tests to see whether DomBB
+  // dominates the value, so adjust DomBB to the normal destination block,
   // which is effectively where the value is first usable.
   BasicBlock *DomBB = Inst.getParent();
   if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
     DomBB = Inv->getNormalDest();
-  if (auto *CPI = dyn_cast<CatchPadInst>(&Inst))
-    DomBB = CPI->getNormalDest();
 
   DomTreeNode *DomNode = DT.getNode(DomBB);
 
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 391ed685766..cb17b603ae5 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1338,19 +1338,22 @@ void llvm::removeUnwindEdge(BasicBlock *BB) {
   if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
     NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
     UnwindDest = CRI->getUnwindDest();
-  } else if (auto *CEP = dyn_cast<CleanupEndPadInst>(TI)) {
-    NewTI = CleanupEndPadInst::Create(CEP->getCleanupPad(), nullptr, CEP);
-    UnwindDest = CEP->getUnwindDest();
-  } else if (auto *CEP = dyn_cast<CatchEndPadInst>(TI)) {
-    NewTI = CatchEndPadInst::Create(CEP->getContext(), nullptr, CEP);
-    UnwindDest = CEP->getUnwindDest();
   } else if (auto *TPI = dyn_cast<TerminatePadInst>(TI)) {
     SmallVector<Value *, 3> TerminatePadArgs;
     for (Value *Operand : TPI->arg_operands())
       TerminatePadArgs.push_back(Operand);
-    NewTI = TerminatePadInst::Create(TPI->getContext(), nullptr,
+    NewTI = TerminatePadInst::Create(TPI->getParentPad(), nullptr,
                                      TerminatePadArgs, TPI);
     UnwindDest = TPI->getUnwindDest();
+  } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
+    auto *NewCatchSwitch = CatchSwitchInst::Create(
+        CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
+        CatchSwitch->getName(), CatchSwitch);
+    for (BasicBlock *PadBB : CatchSwitch->handlers())
+      NewCatchSwitch->addHandler(PadBB);
+
+    NewTI = NewCatchSwitch;
+    UnwindDest = CatchSwitch->getUnwindDest();
   } else {
     llvm_unreachable("Could not find unwind successor");
   }
@@ -1358,6 +1361,7 @@ void llvm::removeUnwindEdge(BasicBlock *BB) {
   NewTI->takeName(TI);
   NewTI->setDebugLoc(TI->getDebugLoc());
   UnwindDest->removePredecessor(BB);
+  TI->replaceAllUsesWith(NewTI);
   TI->eraseFromParent();
 }
 
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index fe9fd18292c..cbb8cf234aa 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3254,8 +3254,8 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
   // updated to continue to the unwind destination of the cleanup pad being
   // simplified.
   BasicBlock *BB = RI->getParent();
-  Instruction *CPInst = dyn_cast<CleanupPadInst>(BB->getFirstNonPHI());
-  if (!CPInst)
+  CleanupPadInst *CPInst = RI->getCleanupPad();
+  if (CPInst->getParent() != BB)
     // This isn't an empty cleanup.
     return false;
 
@@ -3265,9 +3265,10 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
     if (!isa<DbgInfoIntrinsic>(I))
       return false;
 
-  // If the cleanup return we are simplifying unwinds to the caller, this
-  // will set UnwindDest to nullptr.
+  // If the cleanup return we are simplifying unwinds to the caller, this will
+  // set UnwindDest to nullptr.
   BasicBlock *UnwindDest = RI->getUnwindDest();
+  Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
 
   // We're about to remove BB from the control flow.  Before we do, sink any
   // PHINodes into the unwind destination.  Doing this before changing the
@@ -3278,7 +3279,7 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
     // First, go through the PHI nodes in UnwindDest and update any nodes that
     // reference the block we are removing
     for (BasicBlock::iterator I = UnwindDest->begin(),
-                              IE = UnwindDest->getFirstNonPHI()->getIterator();
+                              IE = DestEHPad->getIterator();
          I != IE; ++I) {
       PHINode *DestPN = cast<PHINode>(I);
 
@@ -3322,7 +3323,7 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
     }
 
     // Sink any remaining PHI nodes directly into UnwindDest.
-    Instruction *InsertPt = UnwindDest->getFirstNonPHI();
+    Instruction *InsertPt = DestEHPad;
     for (BasicBlock::iterator I = BB->begin(),
                               IE = BB->getFirstNonPHI()->getIterator();
          I != IE;) {
@@ -3492,18 +3493,16 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
         }
     } else if ((isa<InvokeInst>(TI) &&
                 cast<InvokeInst>(TI)->getUnwindDest() == BB) ||
-               isa<CatchEndPadInst>(TI) || isa<TerminatePadInst>(TI)) {
+               isa<TerminatePadInst>(TI) || isa<CatchSwitchInst>(TI)) {
       removeUnwindEdge(TI->getParent());
       Changed = true;
-    } else if (isa<CleanupReturnInst>(TI) || isa<CleanupEndPadInst>(TI)) {
+    } else if (isa<CleanupReturnInst>(TI)) {
       new UnreachableInst(TI->getContext(), TI);
       TI->eraseFromParent();
       Changed = true;
     }
-    // TODO: If TI is a CatchPadInst, then (BB must be its normal dest and)
-    // we can eliminate it, redirecting its preds to its unwind successor,
-    // or to the next outer handler if the removed catch is the last for its
-    // catchendpad.
+    // TODO: We can remove a catchswitch if all it's catchpads end in
+    // unreachable.
   }
 
   // If this block is now dead, remove it.