[llvm-bugs] [Bug 40949] New: opt cannot terminate with "opt -mem2reg -loop-unswitch -reg2mem -licm -structurizecfg -reg2mem -licm"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40949

            Bug ID: 40949
           Summary: opt cannot terminate with "opt -mem2reg -loop-unswitch
                    -reg2mem -licm -structurizecfg -reg2mem -licm"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: cszide at 163.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 21558
  --> https://bugs.llvm.org/attachment.cgi?id=21558&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:  8512 Killed           
      "$@"

Compiler returned: 137

opt 7:
compiler-explorer/c-preload/compiler-wrapper: line 21: 13372 Killed            
     "$@"

Compiler returned: 137

opt 6:
/compiler-explorer/c-preload/compiler-wrapper: line 21: 18355 Killed           
      "$@"

Compiler returned: 137

The followings are my test environment and test steps.

$clang -v
clang version 9.0.0 (trunk 355281)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm/build4/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 -mem2reg -loop-unswitch -reg2mem -licm -structurizecfg -reg2mem -licm 
small.bc -o small-opt.bc

The following is the source code of small.c

#include "csmith.h"
a() {
  int32_t b[8];
  uint32_t c;
  uint64_t d = 4073709551610;
  for (;;) {
    uint8_t e;
    for (; 8;)
      for (;; c++) {
        if (b)
          return 0;
        if (d)
          break;
      }
  }
}

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