llvm dev - Dec 2021 - What is the difference between bitcode file and naive output file which is compiled with -flto option from same c file?

Hello everyone:    I have known that when a file(for example:
a.c) is compiled with -flto flag, llvm will output a bitcode file(a.o), command
is (clang -flto -c a.c -o a.o). Then I compile same file to bitcode file a.bc,
command is (clang -emit-llvm -o a.bc -c a.c). I want to know what difference
between a.o and a.bc ?
a.c content is like below:
```
#include "a.h"


static signed int i = 0;


void foo2(void) {
  i = -1;
}


static int foo3() {
  foo4();
  return 10;
}


int foo1(void) {
  int data = 0;


&nbsp; if (i < 0)
&nbsp; &nbsp; data = foo3();


&nbsp; data = data + 42;
&nbsp; return data;
}

```
Thanks
lzx
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