LLVM IR basic blocks meaningful names

Question

I'm trying to have meaningful names for the basic blocks in LLVM IR. That is, instead of the name 6 for this loop header, I would like it to be something like: loop.header.6. I'm pretty sure previous llvm/opt versions had this option, but I can't seem to find it in llvm-13. The actual source code for this is probably irrelevant, but given below for completeness

$ sed -n "18,23p" main.ll
6:                                                ; preds = %27, %1
  %7 = load i32, i32* %4, align 4
  %8 = load i32, i32* %3, align 4
  %9 = icmp slt i32 %7, %8
  br i1 %9, label %10, label %30

Source code + compilation flags:

$ cat ~/main.cpp
#include <stdio.h>
bool isPrime(int p) {
    for (int i=2;i<p;i++)
        for (int j=2;j<p;j++)
            if (i*j == p)
                return 0;
    return 1; }
int main(int argc, char **argv) {
    printf("%d\n", isPrime(7));
}
$ ./clang -O0 -c -emit-llvm ~/main.cpp -o main.bc
$ ./llvm-dis ./main.bc -o main.ll

Answer 1

The value names are only added by a frontend (clang) if it is compiled in debug mode / with assertions enabled.

Note that the names might become misleading after optimizations, etc.