[llvm-bugs] [Bug 52240] New: Variable's value late availability after SimplifyCFG at Os

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52240

            Bug ID: 52240
           Summary: Variable's value late availability after SimplifyCFG
                    at Os
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: cristianassaiante at outlook.com
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Variable l_47 value is not available at line 9 even if it has been assigned.
The value become available again at line 10.
>From bisect, this behavior may be caused by SimplifyCFGPass on function (main).

$ cat a.c
int a,  c,  d;
int *b[4];
int main() 
  {
  int f; {
    int *l_47 = &a;
    int e = 0;
    for (; e < 4; e++)
      b[e] = &a;
    f =  c;
  }
  d = f; }

$ clang -v
clang version 13.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ lldb -v
lldb version 13.0.0

$ clang -g -Os -o opt a.c
$ lldb opt
(lldb) target create "opt"
Current executable set to '/home/stepping/64/reduce/opt' (x86_64).
(lldb) b 6
Breakpoint 1: where = opt`main at a.c:9:12, address = 0x0000000000400478
(lldb) run
Process 282 launched: '/home/stepping/64/reduce/opt' (x86_64)
Process 282 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.1
    frame #0: 0x0000000000400478 opt`main at a.c:9:12
   6        int *l_47 = &a;
   7        int e = 0;
   8        for (; e < 4; e++)
-> 9          b[e] = &a;
   10       f =  c;
   11     }
   12     d = f; }
(lldb) frame var
(int) f = <variable not available>

(int) e = 0
(int *) l_47 = <variable not available>

(lldb) n
Process 282 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x0000000000400497 opt`main at a.c:10:10
   7        int e = 0;
   8        for (; e < 4; e++)
   9          b[e] = &a;
-> 10       f =  c;
   11     }
   12     d = f; }
(lldb) frame var
(int) f = <variable not available>

(int) e = 0
(int *) l_47 = 0x0000000000601040

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