[llvm-bugs] [Bug 47215] New: Common code between acquire-release not sunk

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47215

            Bug ID: 47215
           Summary: Common code between acquire-release not sunk
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: hiraditya at msn.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

$ cat test.cpp
```
struct foo {
    [[gnu::weak]] foo() noexcept;
    [[gnu::weak]] ~foo();
    foo* begin() { return this; }
    foo* end() { return this; }
};

__attribute__((noinline))
void bar(foo* i, foo* j) {}

foo* go_leaky() { static foo *f = new foo(); return f; }

int main() {
    bar(go_leaky()->begin(), go_leaky()->end());
    return 0;
}
```

Interesting disassembly code: with clang++ -O3 -std=c++17 -fno-exceptions

```
main:
 push   rbx
 mov    al,BYTE PTR [rip+0x2e81]        # 404058 <guard variable for
go_leaky()::f>
 test   al,al
 je     4011e9 <main+0x19>
 mov    al,BYTE PTR [rip+0x2e77]        # 404058 <guard variable for
go_leaky()::f>
 test   al,al
 je     40121f <main+0x4f>
 xor    eax,eax
 pop    rbx
 ret    
 mov    edi,0x404058
 call   401060 <__cxa_guard_acquire at plt> /// < -------start of acquire-release
 test   eax,eax
 je     4011db <main+0xb>
 mov    edi,0x1
 call   401050 <operator new(unsigned long)@plt>
 mov    rbx,rax
 mov    rdi,rax
 call   401030 <foo::foo()@plt>
 mov    QWORD PTR [rip+0x2e3d],rbx        # 404050 <go_leaky()::f>
 mov    edi,0x404058
 call   401040 <__cxa_guard_release at plt> /// < -------end of acquire-release
 jmp    4011db <main+0xb>
 mov    edi,0x404058
 call   401060 <__cxa_guard_acquire at plt> /// < -------start of acquire-release
 test   eax,eax
 je     4011e5 <main+0x15>
 mov    edi,0x1
 call   401050 <operator new(unsigned long)@plt>
 mov    rbx,rax
 mov    rdi,rax
 call   401030 <foo::foo()@plt>
 mov    QWORD PTR [rip+0x2e07],rbx        # 404050 <go_leaky()::f>
 mov    edi,0x404058
 call   401040 <__cxa_guard_release at plt> /// < -------end of acquire-release
 xor    eax,eax
 pop    rbx
 ret    
 nop    WORD PTR [rax+rax*1+0x0]```

The compiler should be able to fold/sink the common code to a common successor.
Even -gvn-sink didn't seem to help.

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