[Bug libstdc++/102573] optimized code removes the underlying elements of the std::initializer_list being copied

["13508417 at qq dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102573

--- Comment #2 from wjf <13508417 at qq dot com> ---
(In reply to Andrew Pinski from comment #1)
> GCC warns:
> <source>: In function 'int main()':
> <source>:9:19: warning: assignment from temporary 'initializer_list' does
> not extend the lifetime of the underlying array [-Winit-list-lifetime]
>     9 |     il = {111, 222};
>       |                   ^
> 
> Plus at runtime with -fsanitize=address:
> 
> =================================================================
> ==1==ERROR: AddressSanitizer: stack-use-after-scope on address
> 0x7ffcff6b4e10 at pc 0x00000040147d bp 0x7ffcff6b4dc0 sp 0x7ffcff6b4db8
> READ of size 4 at 0x7ffcff6b4e10 thread T0
>     #0 0x40147c in main /app/example.cpp:13
>     #1 0x7f5915fc70b2 in __libc_start_main
> (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
>     #2 0x40118d in _start (/app/output.s+0x40118d)
> 
> Address 0x7ffcff6b4e10 is located in stack of thread T0 at offset 32 in frame
>     #0 0x401255 in main /app/example.cpp:7
> 
>   This frame has 2 object(s):
>     [32, 40) '<unknown>' <== Memory access at offset 32 is inside this
> variable
>     [64, 80) 'il' (line 8)
> HINT: this may be a false positive if your program uses some custom stack
> unwind mechanism, swapcontext or vfork
>       (longjmp and C++ exceptions *are* supported)
> SUMMARY: AddressSanitizer: stack-use-after-scope /app/example.cpp:13 in main
> Shadow bytes around the buggy address:
>   0x10001fece970: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece990: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece9a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece9b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1
> =>0x10001fece9c0: f1 f1[f8]f2 f2 f2 00 00 f3 f3 00 00 00 00 00 00
>   0x10001fece9d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece9e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fece9f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fecea00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x10001fecea10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> Shadow byte legend (one shadow byte represents 8 application bytes):
>   Addressable:           00
>   Partially addressable: 01 02 03 04 05 06 07 
>   Heap left redzone:       fa
>   Freed heap region:       fd
>   Stack left redzone:      f1
>   Stack mid redzone:       f2
>   Stack right redzone:     f3
>   Stack after return:      f5
>   Stack use after scope:   f8
>   Global redzone:          f9
>   Global init order:       f6
>   Poisoned by user:        f7
>   Container overflow:      fc
>   Array cookie:            ac
>   Intra object redzone:    bb
>   ASan internal:           fe
>   Left alloca redzone:     ca
>   Right alloca redzone:    cb
> ==1==ABORTING
> initializer_list size: 2
> initializer_list underlying elements: 
> 
> 
> clang also errors out the same way.

----

Hi Andrew,

I know that adding "-fsanitize=address" could detect the stack-use-after-scope
in runtime. But why not just delete the copy member in std::initializer_list
implementation? I don't see much sense to permit the copy operation.