[PATCH] D63972: [CodeGen] Do the Simple Early Return in block-placement pass to optimize the blocks

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang added a comment.

In D63972#1606967 <https://reviews.llvm.org/D63972#1606967>, @efriedma wrote:

> > Here, if I use F->erase(TBB), the memory leak error is still existed.
>
> What exactly is leaking? (If you're calling erase(), it isn't the MBB itself.)
>
> Of course, that isn't a substitute for calling `FunctionChain.remove` etc.
>
> Looking over this patch again, some of the other work involved in updating various data structures isn't complete here; the MachineDominatorTree/MachinePostDominatorTree isn't updated, MachineLoopInfo isn't updated.


I have made a mistake to say `if I use F->erase(TBB), the memory leak error is still existed.`.

The memory leak is TBB. I should say that if I use `F->remove()`, I will get `memory leak error`, but If use `F->erase(TBB)`, the `memory leak error` will disappear, but I will get `ERROR: AddressSanitizer: use-after-poison`.

Analyse the `ERROR: AddressSanitizer: use-after-poison` when using `F->erase(TBB)`

  2714   for (MachineBasicBlock *ChainBB : FunctionChain) {
  2715     Cond.clear();
  2716     MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
  2717     if (!TII->analyzeBranch(*ChainBB, TBB, FBB, Cond, /*AllowModify*/ true)) {

If I use `F->erase(TBB)`, the `FunctionChain` still has the element which I have removed, so I will get the `ERROR: AddressSanitizer: use-after-poison` when call `2717     if (!TII->analyzeBranch(*ChainBB, TBB, FBB, Cond, /*AllowModify*/ true)) {`.
I should remember those empty BasicBlocks,  and do the clean work  after the `2714 for loop` exit.


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