[llvm-bugs] [Bug 37861] New: Analyzer crashes (Unexpected CFG element at front of block) with widen-loops=true

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37861

            Bug ID: 37861
           Summary: Analyzer crashes (Unexpected CFG element at front of
                    block) with widen-loops=true
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
          Assignee: dcoughlin at apple.com
          Reporter: warren_ristow at playstation.sony.com
                CC: llvm-bugs at lists.llvm.org

The following test-case crashes in the Static Analyzer with an UNREACHABLE:
  Unexpected CFG element at front of block

when widen-loops=true.

$ cat t.cpp
//////////////// "t.cpp" ///////////////
class A {
public:
  void m_fn1();
};
bool g;
void fn1() {
  A a;
  A *b = &a;
  for (;;) {
    g = !b;
    b->m_fn1();
  }
}
////////////////////////////////////////
$ clang --analyze -Xanalyzer -analyzer-config -Xanalyzer widen-loops=true t.cpp
Unexpected CFG element at front of block
UNREACHABLE executed at clang/lib/StaticAnalyzer/Core/PathDiagnostic.cpp:740!
Stack dump:
  ...
clang: error: clang frontend command failed due to signal ...
clang version 7.0.0 (trunk 335000)
Target: x86_64-unknown-linux-gnu
  ...
$

As an aside, prior to r319333 it crashed with a different UNREACHABLE, but in
the same area of "StaticAnalyzer/Core/PathDiagnostic.cpp":
  Unexpected ProgramPoint

That "Unexpected ProgramPoint" crash was reported with a different test-case,
as bug 25609.  Just cross-referencing here, since they may be related.

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