The default of the dispatch switch statement was to branch to a BB that executed

the 'unwind' instruction. However, later on that instruction was converted into
a jump to the basic block it was located in, causing an infinite loop when we
get there.

It turns out, we get there if the _Unwind_Resume_or_Rethrow call returns (which
it's not supposed to do). It returns if it cannot find a place to unwind
to. Thus we would get what appears to be a "hang" when in reality it's just that
the EH couldn't be propagated further along.

Instead of infinitely looping (or calling `unwind', which none of our back-ends
support (it's lowered into nothing...)), call the @llvm.trap() intrinsic
instead. This may not conform to specific rules of a particular language, but
it's rather better than infinitely looping.

<rdar://problem/9175843&9233582>

llvm-svn: 129302

1 files changed, 8 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SjLjEHPrepare.cpp b/llvm/lib/CodeGen/SjLjEHPrepare.cpp
index aaa8568c2f2..43904a76cf1 100644
--- a/llvm/lib/CodeGen/SjLjEHPrepare.cpp
+++ b/llvm/lib/CodeGen/SjLjEHPrepare.cpp
@@ -443,16 +443,17 @@ bool SjLjEHPass::insertSjLjEHSupport(Function &F) {
     BasicBlock::Create(F.getContext(), "eh.sjlj.setjmp.catch", &F);
 
   // Insert a load of the callsite in the dispatch block, and a switch on its
-  // value.  By default, we go to a block that just does an unwind (which is the
-  // correct action for a standard call).
-  BasicBlock *UnwindBlock =
-    BasicBlock::Create(F.getContext(), "unwindbb", &F);
-  Unwinds.push_back(new UnwindInst(F.getContext(), UnwindBlock));
+  // value. By default, we issue a trap statement.
+  BasicBlock *TrapBlock =
+    BasicBlock::Create(F.getContext(), "trapbb", &F);
+  CallInst::Create(Intrinsic::getDeclaration(F.getParent(), Intrinsic::trap),
+                   "", TrapBlock);
+  new UnreachableInst(F.getContext(), TrapBlock);
 
   Value *DispatchLoad = new LoadInst(CallSite, "invoke.num", true,
                                      DispatchBlock);
   SwitchInst *DispatchSwitch =
-    SwitchInst::Create(DispatchLoad, UnwindBlock, Invokes.size(),
+    SwitchInst::Create(DispatchLoad, TrapBlock, Invokes.size(),
                        DispatchBlock);
   // Split the entry block to insert the conditional branch for the setjmp.
   BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
@@ -561,7 +562,7 @@ bool SjLjEHPass::insertSjLjEHSupport(Function &F) {
   // Replace all unwinds with a branch to the unwind handler.
   // ??? Should this ever happen with sjlj exceptions?
   for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
-    BranchInst::Create(UnwindBlock, Unwinds[i]);
+    BranchInst::Create(TrapBlock, Unwinds[i]);
     Unwinds[i]->eraseFromParent();
   }