[PATCH] D15798: Fix for Bug 24852 (crash with -debug -instcombine)

[Duncan P. N. Exon Smith via llvm-commits]

> On 2016-Jan-06, at 14:28, Mehdi AMINI <mehdi.amini at apple.com> wrote:
> 
> joker.eph added a comment.
> 
> David: I have the same question. It turns out that to reproduce you need to print an instruction that has a metadata attached, but does not have a parent.

That seems easier to reproduce with a unit test rather than a
lit test.

> 
> Here is the offending code in InstCombine (with comment from me on what happens):
> 
>  DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
>  DEBUG(dbgs() << "IC: Visiting: " << OrigI << '\n');
> 
>  if (Instruction *Result = visit(*I)) {   // <-- Result does not have a parent, neither a dbgloc at this point
>    ++NumCombined;
>    // Should we replace the old instruction with a new one?
>    if (Result != I) {
>      DEBUG(dbgs() << "IC: Old = " << *I << '\n'
>                   << "    New = " << *Result << '\n');      // <-- This print succeed because there is no debug location
> 
>      if (I->getDebugLoc())
>        Result->setDebugLoc(I->getDebugLoc());   // <-- here we set the debug location, still no parent
>      // Everything uses the new instruction now.
>      I->replaceAllUsesWith(Result);    // <- we are in a state where we have user but still no parent, is it valid?
> 
>      // Move the name to the new instruction first.
>      Result->takeName(I);
> 
>      // Push the new instruction and any users onto the worklist.
>      Worklist.Add(Result);               // <- This is where we will try to print again, but this time with a debug location and no parent (->crash)
>      Worklist.AddUsersToWorkList(*Result);
> 
>      // Insert the new instruction into the basic block...
>      BasicBlock *InstParent = I->getParent();
>      BasicBlock::iterator InsertPos = I->getIterator();
> 
> 
> http://reviews.llvm.org/D15798
> 
> 
>