[llvm-bugs] [Bug 41542] New: Broken function found with "opt -lowerswitch -loop-instsimplify -jump-threading -loop-versioning-licm"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41542

            Bug ID: 41542
           Summary: Broken function found with "opt -lowerswitch
                    -loop-instsimplify  -jump-threading
                    -loop-versioning-licm"
           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 21802
  --> https://bugs.llvm.org/attachment.cgi?id=21802&action=edit
.bc file of the source code

$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 -lowerswitch -loop-instsimplify -jump-threading -loop-versioning-licm
small.bc -o small-opt.bc
PHI nodes must have at least one entry.  If the block is dead, the PHI should
be removed!
  %.lcssa = phi i32 
in function f
LLVM ERROR: Broken function found, compilation aborted!

By using godbolt, it shows that llvm 7/trunk version have this problem, but
llvm 6 is fine.

--------------------------------------------------------
struct a {};
struct {
  int b;
} c, d;
int e;
int f() {
  int g;
  for (; 7;)
  h:;
  {
    struct a *i[1];
    struct a j;
    int k[1];
    for (; e;)
      for (; g; g++)
        i[g] = &c;
    k[e] = 6;
    if (d.b)
      goto h;
    for (; 0;)
      return 0;
  }
}

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