[WinEHPrepare] Replace unreasonable funclet terminators with unreachable

It is possible to be in a situation where more than one funclet token is
a valid SSA value.  If we see a terminator which exits a funclet which
doesn't use the funclet's token, replace it with unreachable.

Differential Revision: http://reviews.llvm.org/D12074

llvm-svn: 245238

1 files changed, 33 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/WinEHPrepare.cpp b/llvm/lib/CodeGen/WinEHPrepare.cpp
index a299c4fcfb1..4fb08ac200e 100644
--- a/llvm/lib/CodeGen/WinEHPrepare.cpp
+++ b/llvm/lib/CodeGen/WinEHPrepare.cpp
@@ -3085,6 +3085,33 @@ bool WinEHPrepare::prepareExplicitEH(Function &F) {
         RemapInstruction(&I, VMap, RF_IgnoreMissingEntries);
   }
 
+  // Remove implausible terminators and replace them with UnreachableInst.
+  for (auto &Funclet : FuncletBlocks) {
+    BasicBlock *FuncletPadBB = Funclet.first;
+    std::set<BasicBlock *> &BlocksInFunclet = Funclet.second;
+    Instruction *FirstNonPHI = FuncletPadBB->getFirstNonPHI();
+    auto *CatchPad = dyn_cast<CatchPadInst>(FirstNonPHI);
+    auto *CleanupPad = dyn_cast<CleanupPadInst>(FirstNonPHI);
+
+    for (BasicBlock *BB : BlocksInFunclet) {
+      TerminatorInst *TI = BB->getTerminator();
+      // CatchPadInst and CleanupPadInst can't transfer control to a ReturnInst.
+      bool IsUnreachableRet = isa<ReturnInst>(TI) && (CatchPad || CleanupPad);
+      // The token consumed by a CatchReturnInst must match the funclet token.
+      bool IsUnreachableCatchret = false;
+      if (auto *CRI = dyn_cast<CatchReturnInst>(TI))
+        IsUnreachableCatchret = CRI->getReturnValue() != CatchPad;
+      // The token consumed by a CleanupPadInst must match the funclet token.
+      bool IsUnreachableCleanupret = false;
+      if (auto *CRI = dyn_cast<CleanupReturnInst>(TI))
+        IsUnreachableCleanupret = CRI->getReturnValue() != CleanupPad;
+      if (IsUnreachableRet || IsUnreachableCatchret || IsUnreachableCleanupret) {
+        new UnreachableInst(BB->getContext(), TI);
+        TI->eraseFromParent();
+      }
+    }
+  }
+
   // Clean-up some of the mess we made by removing useles PHI nodes, trivial
   // branches, etc.
   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE;) {
@@ -3094,9 +3121,6 @@ bool WinEHPrepare::prepareExplicitEH(Function &F) {
     MergeBlockIntoPredecessor(BB);
   }
 
-  // TODO: Do something about cleanupblocks which branch to implausible
-  // cleanuprets.
-
   // We might have some unreachable blocks after cleaning up some impossible
   // control flow.
   removeUnreachableBlocks(F);
@@ -3215,6 +3239,12 @@ void WinEHPrepare::insertPHIStore(
 void WinEHPrepare::demoteNonlocalUses(Value *V,
                                       std::set<BasicBlock *> &ColorsForBB,
                                       Function &F) {
+  // Tokens can only be used non-locally due to control flow involving
+  // unreachable edges.  Don't try to demote the token usage, we'll simply
+  // delete the cloned user later.
+  if (isa<CatchPadInst>(V) || isa<CleanupPadInst>(V))
+    return;
+
   DenseMap<BasicBlock *, Value *> Loads;
   AllocaInst *SpillSlot = nullptr;
   for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); UI != UE;) {