[LLVMbugs] [Bug 4398] New: passManager should always call releaseMemory to avoid use-after-free bugs

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=4398

           Summary: passManager should always call releaseMemory to avoid
                    use-after-free bugs
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: edwintorok at gmail.com
                CC: gohman at apple.com, llvmbugs at cs.uiuc.edu


Currently some passes call releaseMemory (or their equivalent) in their run
function, some don't (for example ScalarEvolution).

According to the documentation "This method is called after the run* method for
the class, before the next call of run* in your pass." 

However the PassManager doesn't do this for on-the-fly passes, which can cause
use-after-free bugs if you are using ScalarEvolution from a ModulePass 
(LoopInfo is rerun, but ScalarEvolution still has stale data from the previous
LoopInfo run).

As discusses on llvm-commits the following should happen:
 - PassManager should call releaseMemory for on-the-fly passes too
 - PassManager should assert if it forgot to call releaseMemory
 - passes that have a releaseMemory equivalent should have the method renamed
to releaseMemory
 - passes should no longer call releaseMemory in their run function


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