Created attachment 53484 [details]
Minimal reproducer

Building `program.ada` with optimisation -O2 or above:

% gnatmake -O2 -flto main.adb

Causes linker warning:
```
gcc -c -O2 -flto main.adb
gcc -c -O2 -flto test.adb
gnatbind -x main.ali
gnatlink main.ali -O2 -flto
test.adb: In function 'test__assign':
test.adb:6:21: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
    6 |       The_Array (1) := AAAAA_Enum;
      |                     ^
test.ads:11:4: note: at offset -9223372036854775808 into destination object 'F' of size 4
   11 |    The_Array : T_Array;
      |    ^
```

The program is essentially:
   type First_Enum is (AAAAA_Enum);
   subtype Second_Enum is First_Enum;
   type T_Array is array (Integer range -1 .. 2) of Second_Enum;
   -- Change 'First to something >= 0 and the warning disappears.
   -- Using the First_Enum instead of Second_Enum and the warning disappears.

GNATMAKE 12.1.0 - cause warning
GNATMAKE 11.2.0 - cause warning
GNATMAKE 10.3.0 - cause no warning