[Bug c++/61597] Unexpected behavior at runtime

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61597

--- Comment #21 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The trunk can detect this with the reduced testcase in comment #16 with
-fsanitize=address (it could not in GCC 12 though):

=================================================================
==1==ERROR: AddressSanitizer: stack-use-after-return on address 0x7fed23a00020
at pc 0x000000401410 bp 0x7ffd3ef98df0 sp 0x7ffd3ef98de8
READ of size 4 at 0x7fed23a00020 thread T0
    #0 0x40140f in main /app/example.cpp:18
    #1 0x7fed26088082 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x24082) (BuildId:
1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #2 0x4010ed in _start (/app/output.s+0x4010ed) (BuildId:
eae82a9845e6e2c7baecc615e9a9cf9fe73eac81)

Address 0x7fed23a00020 is located in stack of thread T0 at offset 32 in frame
    #0 0x4011b5 in func(Iter, int) /app/example.cpp:11

  This frame has 1 object(s):
    [32, 36) 'iter' (line 11) <== Memory access at offset 32 is inside this
variable
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-return /app/example.cpp:18 in main
Shadow bytes around the buggy address:
  0x7fed239ffd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed239ffe00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed239ffe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed239fff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed239fff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x7fed23a00000: f5 f5 f5 f5[f5]f5 f5 f5 00 00 00 00 00 00 00 00
  0x7fed23a00080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed23a00100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed23a00180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed23a00200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7fed23a00280: 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