[llvm-bugs] [Bug 45118] New: Verifier - nullptr dereference warning

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45118

            Bug ID: 45118
           Summary: Verifier - nullptr dereference warning
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Core LLVM classes
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: anemet at apple.com, aprantl at apple.com,
                    llvm-bugs at lists.llvm.org, orlando.hyams at sony.com

http://lab.llvm.org:8080/coverage/coverage-reports/llvm/coverage/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/lib/IR/Verifier.cpp.html

Static analysis warns that the SP variable is dereferenced as null:

    DILocalScope *Scope = DL->getInlinedAtScope();
    if (Scope && !Seen.insert(Scope).second)
      return;

    DISubprogram *SP = Scope ? Scope->getSubprogram() : nullptr;

    // Scope and SP could be the same MDNode and we don't want to skip
    // validation in that case
    if (SP && ((Scope != SP) && !Seen.insert(SP).second))
      return;

    AssertDI(SP->describes(&F),
             "!dbg attachment points at wrong subprogram for function", N, &F,
             &I, DL, Scope, SP);

AFAICT the Scope variable will always be non-null (and we should just assert
that it is), allowing us to simplify the code to something like the below (my
main concern is I'm not sure on how the verifier assertions are supposed to be
implemented):

    DILocalScope *Scope = DL->getInlinedAtScope();
    assert(Scope && "Unknown inlined scope"); <-- NOT FAMILIAR WITH THE
VERIFIER ASSERTION MECHANISM
    if (!Seen.insert(Scope).second)
      return;

    DISubprogram *SP = Scope->getSubprogram();
    assert(SP && "Unknown scope subprogram"); <-- NOT FAMILIAR WITH THE
VERIFIER ASSERTION MECHANISM

    // Scope and SP could be the same MDNode and we don't want to skip
    // validation in that case
    if (((Scope != SP) && !Seen.insert(SP).second))
      return;

    AssertDI(SP->describes(&F),
             "!dbg attachment points at wrong subprogram for function", N, &F,
             &I, DL, Scope, SP);

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