[llvm-commits] [llvm] r168581 - /llvm/trunk/lib/VMCore/PassManager.cpp

[Chandler Carruth]

Zhou, this patch was never removed. Please do not commit patches without
review first. Please revert and ping the review thread.

While it might seem like this patch is "obvious" two things make it clear
that it is not:

On Sun, Nov 25, 2012 at 9:45 PM, Zhou Sheng <zhousheng00 at gmail.com> wrote:

> Author: sheng
> Date: Sun Nov 25 23:45:53 2012
> New Revision: 168581
>
> URL: http://llvm.org/viewvc/llvm-project?rev=168581&view=rev
> Log:
> Fix a PassManager pointer use-after-free bug.
> The bug can be triggered when we require LoopInfo analysis ahead of
> DominatorTree construction in a Module Pass.


Then you should include a test case which demonstrates the bug under
valgrind, or some other use-after-free detection system.


> The cause is that the LoopInfo analysis itself also invokes DominatorTree
> construction, therefore, when PassManager schedules LoopInfo, it will add
> DominatorTree first. Then after that, when the PassManger turns to schedule
> DominatorTree invoked by the above ModulePass, it finds there is already a
> DominatorTree, so it delete the redundant one. However, somehow it still
> try to access that pass pointer after free as code pasted below, which
> results in segment fault.
>

"somehow" isn't a good enough explanation for this fix being the correct
fix. You need to actually understand the complete issue. Also, the comments
below don't really seem to match your description here.


Anyways, we should take the rest of this to the code review thread, and
continue there until the review is complete before committing.
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