[llvm-bugs] [Bug 40937] New: opt cannot terminate with "opt -instcombine -structurizecfg -loop-extract -loop-rotate -newgvn -loop-versioning -loop-extract"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40937

            Bug ID: 40937
           Summary: opt cannot terminate with "opt -instcombine
                    -structurizecfg -loop-extract -loop-rotate -newgvn
                    -loop-versioning -loop-extract"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: cszide at 163.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 21553
  --> https://bugs.llvm.org/attachment.cgi?id=21553&action=edit
.bc file of the source code

For this test case, opt cannot terminate. I have tested it using godbolt, and
the opt 6/7/truck versions all have this problem. The outputs of opt 6/7/truck
are as follows.

opt truck:
/compiler-explorer/c-preload/compiler-wrapper: line 21: 20300 Killed           
      "$@"

Compiler returned: 137

opt 7:
/compiler-explorer/c-preload/compiler-wrapper: line 21: 20621 Killed           
      "$@"

Compiler returned: 137

opt 6:
/compiler-explorer/c-preload/compiler-wrapper: line 21: 12475 Killed           
      "$@"

Compiler returned: 137

The followings are my test environment and test steps.

$clang -v
clang version 9.0.0 (trunk 354742)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm/build/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64

$clang -O3 -c -emit-llvm  -mllvm -disable-llvm-optzns small.c -o small.bc

$opt -instcombine -structurizecfg -loop-extract -loop-rotate -newgvn
-loop-versioning -loop-extract  small.bc -o small-opt.bc

The following is the source code of small.c
a;
b() {
  int c = 0;
  for (; c; ++c)
    if (a)
      break;
}

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