[llvm-bugs] [Bug 31186] New: opt crashes with "opt -loop-rotate -licm -loop-unroll -loop-vectorize": Assertion `Headers.size() >= 2 && "Expected irreducible CFG; -loop-info is likely invalid"' failed

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31186

            Bug ID: 31186
           Summary: opt crashes with "opt -loop-rotate -licm -loop-unroll
                    -loop-vectorize": Assertion `Headers.size() >= 2 &&
                    "Expected irreducible CFG; -loop-info is likely
                    invalid"' failed
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

$ clang -v
clang version 4.0.0 (trunk 287975)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/clang-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.2.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang -c -emit-llvm -o small.bc small.c
$ opt -loop-rotate -licm -loop-unroll -loop-vectorize -o small-opt.bc small.bc
opt:
/tmp/llvm-builder/llvm-source-trunk/lib/Analysis/BlockFrequencyInfoImpl.cpp:670:
void findIrreducibleHeaders(const llvm::BlockFrequencyInfoImplBase&, const
llvm::bfi_detail::IrreducibleGraph&, const std::vector<const
llvm::bfi_detail::IrreducibleGraph::IrrNode*>&,
llvm::BlockFrequencyInfoImplBase::LoopData::NodeList&,
llvm::BlockFrequencyInfoImplBase::LoopData::NodeList&): Assertion
`Headers.size() >= 2 && "Expected irreducible CFG; -loop-info is likely
invalid"' failed.
#0 0x0000000001c45a45 (opt+0x1c45a45)
#1 0x0000000001c43b2e (opt+0x1c43b2e)
#2 0x0000000001c43c90 (opt+0x1c43c90)
#3 0x00007fce8a932330 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x10330)
#4 0x00007fce8971ec37 gsignal
/build/eglibc-oGUzwX/eglibc-2.19/signal/../nptl/sysdeps/unix/sysv/linux/raise.c:56:0
#5 0x00007fce89722028 abort
/build/eglibc-oGUzwX/eglibc-2.19/stdlib/abort.c:91:0
#6 0x00007fce89717bf6 __assert_fail_base
/build/eglibc-oGUzwX/eglibc-2.19/assert/assert.c:92:0
#7 0x00007fce89717ca2 (/lib/x86_64-linux-gnu/libc.so.6+0x2fca2)
#8 0x0000000001290c8d (opt+0x1290c8d)
#9 0x0000000001286718 (opt+0x1286718)
#10 0x0000000001286dc0 (opt+0x1286dc0)
#11 0x000000000128704d (opt+0x128704d)
#12 0x00000000017dfe83 (opt+0x17dfe83)
#13 0x00000000017dff2c (opt+0x17dff2c)
#14 0x00000000017e0bda (opt+0x17e0bda)
#15 0x000000000078c9a1 (opt+0x78c9a1)
#16 0x00007fce89709f45 __libc_start_main
/build/eglibc-oGUzwX/eglibc-2.19/csu/libc-start.c:321:0
#17 0x00000000007e6f4b (opt+0x7e6f4b)
Stack dump:
0.      Program arguments: opt -loop-rotate -licm -loop-unroll -loop-vectorize
-o small-opt.bc small.bc 
1.      Running pass 'Function Pass Manager' on module 'small.bc'.
2.      Running pass 'Block Frequency Analysis' on function '@fn1'
Aborted (core dumped)
$ 


--------------------------------


int a, b;

void fn1 ()
{
  for (; a; a++)
    while (1) 
      {
        while (b) 
          ;
        if (a)
          break;
      }
}

int main ()
{
  fn1 ();
  return 0; 
}

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