[llvm-bugs] [Bug 39746] New: Crash - reinterpret_cast<> from forward declared class followed by array access

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39746

            Bug ID: 39746
           Summary: Crash - reinterpret_cast<> from forward declared class
                    followed by array access
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: kobalicek.petr at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Sample code, compiled by clang 7 and trunk:

struct Something;
extern Something xxx[32];

class C {
public:
  void* p;
};

const C& f() noexcept {
  return reinterpret_cast<const C*>(xxx)[16];
}

Compiler explorer reproducible:

https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(j:1,lang:c%2B%2B,source:'%0Astruct+Something%3B%0A%0Aextern+Something+xxx%5B32%5D%3B%0A%0Aclass+C+%7B%0Apublic:%0A++void*+p%3B%0A%7D%3B%0A%0Aconst+C%26+f()+noexcept+%7B%0A++return+reinterpret_cast%3Cconst+C*%3E(xxx)%5B16%5D%3B%0A%7D'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),k:50,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:clang_trunk,filters:(b:'0',binary:'1',commentOnly:'0',demangle:'0',directives:'0',execute:'1',intel:'0',trim:'1'),lang:c%2B%2B,libs:!(),options:'-O3',source:1),l:'5',n:'0',o:'x86-64+clang+(trunk)+(Editor+%231,+Compiler+%231)+C%2B%2B',t:'0')),k:50,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4

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