[llvm-bugs] [Bug 34929] New: AST being modified while iteration

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https://bugs.llvm.org/show_bug.cgi?id=34929

            Bug ID: 34929
           Summary: AST being modified while iteration
           Product: libraries
           Version: 3.8
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: vbganesh79 at gmail.com
                CC: llvm-bugs at lists.llvm.org

In the LICM.cpp, we see that the AST (AliasSet Tracker) object is being
iterated over all the alias sets it contains and modified at the same time (in
LLVM 3.8). We like to know if it is safe to do so. 

We have a similar usage of AST in a transformation we developed and that causes
crashes. Additionally, we also see LICM crash sometimes but never able to
reproduce deterministic. So we think this style of using AST tracker object
might be a potential bug. We very well are aware of the fact that without
reproduction steps it's impossible to debug. However, if we can be assured that
it is safe to mutate AST object while iterating over the alias sets of the
object, at least we can eliminate this possibility for the crash.

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