[llvm-bugs] [Bug 25217] New: GlobalsAAResult possible dangling reference

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25217

            Bug ID: 25217
           Summary: GlobalsAAResult possible dangling reference
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: yaron.keren at gmail.com
                CC: chandlerc at gmail.com, llvm-bugs at lists.llvm.org
    Classification: Unclassified

lib/Analysis/GlobalsModRef.cpp:491 sets FunctionInfo &FI as reference into the
DenseMap FunctionInfos. 

    FunctionInfo &FI = FunctionInfos[SCC[0]->getFunction()];

lib/Analysis/GlobalsModRef.cpp:590 copies FI into all FunctionInfo[SCC
members].

    for (unsigned i = 1, e = SCC.size(); i != e; ++i)
      FunctionInfos[SCC[i]->getFunction()] = FI;

DenseMap iterators are not stable and the loop could potentially invalidate the
reference FI, continuing using the invalidated reference.

Practically, that may be a rare case since 1) FunctionInfos may already have
all the required entries 2) DenseMap iterators are usually stable even when
inserting entry 3) The invalidate reference may still contain the right data.

The issue could be fixed by keeping a local copy of FI

    FunctionInfo StackFI = FI;
    for (unsigned i = 1, e = SCC.size(); i != e; ++i)
      FunctionInfos[SCC[i]->getFunction()] = StackFI;

or not using the unstable reference FI while inserting entries

    for (unsigned i = 1, e = SCC.size(); i != e; ++i)
      FunctionInfos[SCC[i]->getFunction()] =
FunctionInfos[SCC[0]->getFunction()];

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