[llvm-bugs] [Bug 42449] New: loop-unroll-and-jam makes function broken with "opt -lowerswitch -inline -globalopt -jump-threading -lcssa -loop-unroll-and-jam"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42449

            Bug ID: 42449
           Summary: loop-unroll-and-jam makes function broken with "opt
                    -lowerswitch -inline -globalopt -jump-threading -lcssa
                    -loop-unroll-and-jam"
           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 22166
  --> https://bugs.llvm.org/attachment.cgi?id=22166&action=edit
.bc file of the source code

$clang -v
clang version 9.0.0 (trunk 363125)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm2/build1/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/7.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64


$clang -O3 -c -emit-llvm -femit-all-decls -mllvm -disable-llvm-optzns small.c

$opt -lowerswitch -inline -globalopt -jump-threading -lcssa
-loop-unroll-and-jam small.bc -o small-opt.bc
PHI nodes must have at least one entry.  If the block is dead, the PHI should
be removed!
  %cleanup.dest24.i5 = phi i32 
in function i
LLVM ERROR: Broken function found, compilation aborted!

------------------------------------------------
int a, c, e, f, g;
long b;
static int d;
unsigned h();
void i() {
  for (;;)
    h();
}
unsigned h() {
j:
  for (;;)
    for (;;) {
      int k;
      a = 0;
      for (; a >= 0; a)
        for (; d <= 0;)
          return e;
      if (f)
        break;
      for (; b;)
        for (;;) {
          int l[] = {1, 1, 1};
          for (; 0;)
            goto j;
          short m[7];
          int n[5];
          m[g];
          n[g];
          if (c)
            break;
          return 0;
        }
    }
}

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