[LLVMdev] LICM ilist question.

Gang-Ryung Uh guh at boisestate.edu
Mon Jan 11 10:57:29 PST 2010

I am using LLVM 2.6 and I have a question on the use of the
BasicBlock::iterator to hoist loop invariant instructions to the loop
preheader. When I process the instructions backward as shown in the
following code, I got the following error right after the "hoist(I)" is
done. Can anyone advise whether I am misusing BasicBlock::iterator?

/opt/llvms/src/llvm_26/ include/llvm/ADT/ilist.h:213:
llvm::ilist_iterator<NodeTy>& llvm::ilist_iterator<NodeTy>::operator--()
[with NodeTy = llvm::Instruction]: Assertion `NodePtr && "--'d off the
beginning of an ilist!"' failed.

*LICM::HOistRegion(DomTreeNode *N)*
    assert(N != 0 && "Null dominator tree node?");
    BasicBlock *BB = N->getBlock();


   * for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) *{

               Instruction &I = *--II;

               if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
                   * hoist(I);*

-- UGR
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