Repository: rust
Issue: LLDB show a non existing variable at O1
Labels: A-debuginfo,E-needs-test,A-macros,T-compiler

LLDB show variable 'res' (when stepping at line 12) that does not exists in the code.

```bash

$ cat -n a.rs 
     1  // run-pass
     2  use std::ptr;
     3  use std::rc::Rc;
     4  use std::sync::Arc;
     5
     6  fn main() {
     7      let p: *const u8 = ptr::null();
     8      let rc = Rc::new(1usize);
     9      let arc = Arc::new(1usize);
    10      let b = Box::new("hi");
    11
    12      let _ = format!("{:p}{:p}{:p}",
    13                      rc, arc, b);
    14
    15      if cfg!(target_pointer_width = "32") {
    16          assert_eq!(format!("{:#p}", p),
    17                     "0x00000000");
    18      } else {
    19          assert_eq!(format!("{:#p}", p),
    20                     "0x0000000000000000");
    21      }
    22      assert_eq!(format!("{:p}", p),
    23                 "0x0");
    24  }

$ cat a.rs 
// run-pass
use std::ptr;
use std::rc::Rc;
use std::sync::Arc;
fn main() {
    let p: *const u8 = ptr::null();
    let rc = Rc::new(1usize);
    let arc = Arc::new(1usize);
    let b = Box::new("hi");
    let _ = format!("{:p}{:p}{:p}",
                    rc, arc, b);
    if cfg!(target_pointer_width = "32") {
        assert_eq!(format!("{:#p}", p),
                   "0x00000000");
    } else {
        assert_eq!(format!("{:#p}", p),
                   "0x0000000000000000");
    }
    assert_eq!(format!("{:p}", p),
               "0x0");
}

$ rustc --version
+rustc 1.46.0-nightly (3503f565e 2020-07-02)

$ lldb -v
lldb version 11.0.0
  clang revision ee26a31e7b02e124d71091d47f2ae624774e5e0a
  llvm revision ee26a31e7b02e124d71091d47f2ae624774e5e0a

$ rustc -g -C opt-level=1 -o opt a.rs

$ lldb opt
lldb opt 
(lldb) target create "opt"
Current executable set to 'opt' (x86_64).
(lldb) b -l 12
Breakpoint 1: 2 locations.
(lldb) r
Process 62 launched: 'opt' (x86_64)
Process 62 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.1
    frame #0: 0x00005555555590f6 opt`a::main::h1122ef72fcd4218b at a.rs:12:13
   9        let arc = Arc::new(1usize);
   10       let b = Box::new("hi");
   11  
-> 12       let _ = format!("{:p}{:p}{:p}",
   13                       rc, arc, b);
   14  
   15       if cfg!(target_pointer_width = "32") {
(lldb) frame var
(unsigned char *) p = <empty constant data>
(alloc::rc::Rc<unsigned long>) rc = <variable not available>
(alloc::sync::Arc<unsigned long>) arc = <variable not available>
(&str *) b = 0x000055555578fa80
(lldb) c
Process 62 resuming
Process 62 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.2
    frame #0: 0x000055555555918f opt`a::main::h1122ef72fcd4218b at a.rs:12:13
   9        let arc = Arc::new(1usize);
   10       let b = Box::new("hi");
   11  
-> 12       let _ = format!("{:p}{:p}{:p}",
   13                       rc, arc, b);
   14  
   15       if cfg!(target_pointer_width = "32") {
(lldb) frame var
(unsigned char *) p = <empty constant data>
(alloc::rc::Rc<unsigned long>) rc = <variable not available>
(alloc::sync::Arc<unsigned long>) arc = <variable not available>
(&str *) b = <variable not available>
(alloc::string::String) res = {
  vec = {
    buf = {
      ptr = (pointer = "0x55555578fa500x55555578fa700x55555578fa80\U00000002", _marker = core::marker::PhantomData<unsigned char> @ 0x00007fffffffe290)
```