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From: "ibrbulat at yandex dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99858] New: Wrong throw-expression behaviour with reference
 to pointer
Date: Wed, 31 Mar 2021 21:21:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99858

            Bug ID: 99858
           Summary: Wrong throw-expression behaviour with reference to
                    pointer
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ibrbulat at yandex dot ru
  Target Milestone: ---

If you catch an exception of pointer type by reference to pointer, change t=
he
value of the pointer inside this catch block and then rethrow it via *throw*
with no operand, compiler will create a copy of initial exception(!) and no
changes will be seen in the next handler.
Minimal example is here https://godbolt.org/z/T11939EYM

This behavior is contrary to the C ++ language standard (e.g. C++17):
[expr.throw]: "... 3. A throw-expression with no operand rethrows the curre=
ntly
handled exception (18.3). The exception is reactivated with the existing
exception object; no new exception object is created. ..."
[except.throw]: "... If a handler exits by rethrowing, control is passed to
another handler for the same exception object.  ..."

However it works well with other (non-pointer) types - no additional copy is
created, all handlers work with the same object and see each other changes
(example: https://godbolt.org/z/Ea6r1z7rE)=