opt error expectedtop-level entity in code, that shouldn't create it

Question

Hello I've got a Problem. I try to use a built-in Pass from LLVM. Just to try it I used the Pass "DeadStoreElimination" dse. For that I wrote a simple code:

#include <stdio.h>

int main() {
  int x = 10;
  int y = 20;

  // Dead Store: Value of X is overwritten before its used
  x = 5;

  // Dead Store: Value y is never used
  y = 30;

  printf("The Value of x is: %d\n", x);

  return 0;
}

after running:

clang -c -o Spectre.bc Spectre.c

I use:

opt -passes=dse Spectre.bc -o Spectre.bc

which results to the Error:

opt: Spectre.bc:1:1: error: expected top-level entity
ELF>�@@    UH���E��E�

Or when I run:

opt -passes=dce Spectre.c -o Spectre.bc

it creates:

opt: Spectre.c:1:1: error: expected top-level entity
#include <stdio.h>
^

Can anyone help me? What am I doing wrong?

As written above I am not getting what I want to get. Other Posts on stackoverflow wouldn't solve my Problem

Answer 1

You need to use --emit-llvm for clang to produce LLVM IR. Still, for DSE likely few other pre-requisite passes would be necessary.