[llvm-bugs] [Bug 52539] New: Emitted binary code changes when -g is enabled at -O2 with -flto

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52539

            Bug ID: 52539
           Summary: Emitted binary code changes when -g is enabled at -O2
                    with -flto
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: tlwang at uwaterloo.ca
                CC: cnsun at uwaterloo.ca, llvm-bugs at lists.llvm.org
            Blocks: 37728

The .text section for the following program (program0_preprocessed.c
) changes after toggling the -g flag.

$ clang-trunk -v
clang version 14.0.0 (https://github.com/llvm/llvm-project.git
82fc4cc60bec6d0eacad7e8575f404dcdf5144c5)
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
$ cat program0_preprocessed.c
int a, e;
int volatile b;
int *c;
short d;
void main() {
  int f;
  for (;;) {
    int g, h;
    int i[6];
    c = i;
    d ^= 4;
    f = d > i[5] ? 0 : d + i[5];
    g = h = f - a;
    int j = 2;
    e = 2 - h;
    b = e;
  }
}
$ clang-trunk -w -flto -O2 program0_preprocessed.c -o a.out; objdump
--disassemble --section=.text a.out > no_g.txt
$ clang-trunk -w -flto -O2 -g program0_preprocessed.c -o a.out; objdump
--disassemble --section=.text a.out > g.txt
$ diff no_g.txt g.txt
98,106c98,105
<   401144:     ba 02 00 00 00          mov    $0x2,%edx
<   401149:     29 f2                   sub    %esi,%edx
<   40114b:     29 fa                   sub    %edi,%edx
<   40114d:     39 fe                   cmp    %edi,%esi
<   40114f:     41 0f 4c d1             cmovl  %r9d,%edx
<   401153:     89 15 e3 2e 00 00       mov    %edx,0x2ee3(%rip)        #
40403c <b>
<   401159:     8b 74 24 fc             mov    -0x4(%rsp),%esi
<   40115d:     eb d1                   jmp    401130 <main+0x20>
<   40115f:     90                      nop
---
>   401144:	8d 0c 3e             	lea    (%rsi,%rdi,1),%ecx
>   401147:	ba 02 00 00 00       	mov    $0x2,%edx
>   40114c:	29 ca                	sub    %ecx,%edx
>   40114e:	39 fe                	cmp    %edi,%esi
>   401150:	41 0f 4c d1          	cmovl  %r9d,%edx
>   401154:	89 15 e2 2e 00 00    	mov    %edx,0x2ee2(%rip)        # 40403c <b>
>   40115a:	8b 74 24 fc          	mov    -0x4(%rsp),%esi
>   40115e:	eb d0                	jmp    401130 <main+0x20>
$


Referenced Bugs:

https://bugs.llvm.org/show_bug.cgi?id=37728
[Bug 37728] [meta] Make llvm passes debug info invariant
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