[llvm-bugs] [Bug 46041] New: Inconsistent debug info between break and stepi at -O1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46041

            Bug ID: 46041
           Summary: Inconsistent debug info between break and stepi at -O1
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: yangyibiao at hust.edu.cn
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Created attachment 23523
  --> https://bugs.llvm.org/attachment.cgi?id=23523&action=edit
the binary

$ clang --version
clang version 11.0.0 (/home/yibiao/.cache/yay/llvm-git/llvm-project
871beba234a83a2a02da9dedbd59b91a1bfbd7af)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

$ lldb --version
lldb version 11.0.0
  clang revision 871beba234a83a2a02da9dedbd59b91a1bfbd7af
  llvm revision 871beba234a83a2a02da9dedbd59b91a1bfbd7af



$ clang -O1 -g small.c

$ lldb a.out
(lldb) target create "a.out"
Current executable set to '/home/yibiao/Debugger/a.out' (x86_64).
(lldb) b 5 
Breakpoint 1: where = a.out`f + 21 at small.c:5:1, address = 0x0000000000401125
(lldb) r
Process 46982 launched: '/home/yibiao/Debugger/a.out' (x86_64)
Process 46982 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401125 a.out`f(x=-216) at small.c:5:1
   2      if (x==-216 || x==-132)
   3         return 1;
   4      return 0;
-> 5    }
   6    
   7    int main () {
   8      volatile int i;
(lldb) fr var x
(int) x = -216
(lldb) 



/************************************
As showed, when setting breakpoint on Line 5 (first hit), the value of "x" is
-216.
However, when step-i to Line 5, the value of "x" is -230 which is as expected:
************************************/



$ clang -O1 -g small.c; lldb a.out
(lldb) target create "a.out"
Current executable set to '/home/yibiao/Debugger/a.out' (x86_64).
(lldb) b main
Breakpoint 1: where = a.out`main + 5 at small.c:9:10, address =
0x0000000000401135
(lldb) r
Process 45549 launched: '/home/yibiao/Debugger/a.out' (x86_64)
Process 45549 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401135 a.out`main at small.c:9:10
   6    
   7    int main () {
   8      volatile int i;
-> 9      for (i = -230; i < -120; i++)
   10       if (f(i) != (i==-216 || i==-132))
   11         return 1;
   12     return 0;
(lldb) si -c 14
Process 45549 stopped
* thread #1, name = 'a.out', stop reason = instruction step into
    frame #0: 0x0000000000401128 a.out`f(x=-230) at small.c:5:1
   2      if (x==-216 || x==-132)
   3         return 1;
   4      return 0;
-> 5    }
   6    
   7    int main () {
   8      volatile int i;
(lldb) fr var x
(int) x = -230
(lldb)



/******************* the small.c *************/

$ cat small.c
int f(int x) {
  if (x==-216 || x==-132)
     return 1;
  return 0;
}

int main () {
  volatile int i;
  for (i = -230; i < -120; i++)
    if (f(i) != (i==-216 || i==-132))
      return 1;
  return 0;
}

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