[llvm-bugs] [Bug 50580] New: Emitted binary code changes when -g is enabled at -O1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50580

            Bug ID: 50580
           Summary: Emitted binary code changes when -g is enabled at -O1
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: tlwang at uwaterloo.ca
                CC: llvm-bugs at lists.llvm.org

The .text section for the following program (program.c) changes after toggling
the -g flag.

$ cat program.c
short a;
int b, c;
long d, e;
long f() {
  long g = ({ d == 0 ? c : c / d; }), h = e;
  int i = b & g;
  if (i) {
    a = 0;
    return b;
  }
  return h;
}
int main() {}
$
$ clang-trunk -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
8a96993da5ef408847505ec2e470805a71c30392)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/cnsun/usr/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$
$ clang-trunk -O1 -w program.c ; objdump --disassemble a.out > "no-g.txt"
$ clang-trunk -O1 -g -w program.c ; objdump --disassemble a.out > "g.txt"
$ diff no-g.txt g.txt
113,115c113,116
<   401141:     48 8b 05 f8 2e 00 00    mov    0x2ef8(%rip),%rax        #
404040 <e>
<   401148:     c3                      retq
<   401149:     0f 1f 80 00 00 00 00    nopl   0x0(%rax)
---
>   401141:	48 8b 0d f8 2e 00 00 	mov    0x2ef8(%rip),%rcx        # 404040 <e>
>   401148:	48 89 c8             	mov    %rcx,%rax
>   40114b:	c3                   	retq
>   40114c:	0f 1f 40 00          	nopl   0x0(%rax)

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