[llvm-dev] Removing a redundant unconditional branch

[Hiroshi Yamauchi via llvm-dev]

Perhaps, you'd need to also check that the block %15 has only one
predecessor and has no other users?

Posting the error message might help.

On Thu, Feb 6, 2020 at 8:17 PM Charitha Saumya via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> I want to remove a redundant unconditional branch from a Function. In the
> following example I want to remove br label %26 and merge them to a
> single basic block.
>
> ; <label>:9:                                      ; preds = %7
>   %10 = fadd float %5, %8
>   %11 = fmul float %5, %8
>   %12 = fadd float %10, %11
>   %13 = fdiv float %5, %8
>   %14 = fadd float %13, %12
>   br label %15
> ; <label>:15:                                     ; preds = %9
>   br label %26
>
> I tried to do this as follow but ended up getting runtime error. Can
> someone help?
>
> Thanks
>
> Charitha
> for(auto it1 = F.begin(); it1 != F.end(); it1++){
>     BasicBlock& bb = *it1;
>     auto BI = dyn_cast<BranchInst>(bb.getTerminator());
>     if(BI && BI->isUnconditional() && bb.size() == 1){
>
>         for (BasicBlock *pred : predecessors(&bb)) {
>             auto predBI = dyn_cast<BranchInst>(pred->getTerminator());
>             if(predBI && predBI->isUnconditional()){
>                     predBI->setSuccessor(0, bb.getSingleSuccessor());
>                     BI->dropAllReferences();
>                     BI->removeFromParent();
>             }
>         }
>     }
>
> }
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