[Bug c++/111245] New: miscompilation: missing assignment when exception thrown

[Bug c++/111245] New: miscompilation: missing assignment when exception thrown

[briangreenery at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111245

            Bug ID: 111245
           Summary: miscompilation: missing assignment when exception
                    thrown
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: briangreenery at gmail dot com
  Target Milestone: ---

gcc version 13.2.0 (Compiler-Explorer-Build-gcc--binutils-2.40) 
Target: x86_64-linux-gnu

It looks like initialization is incorrectly skipped when:

* The initialization is overwritten by an unconditional assignment from a
function
* However, that function throws an exception which avoids the assignment

The following code should return 5, but it returns random garbage on -O1 or
-O2.

https://godbolt.org/z/T3qTnheYW

# 0 "/app/example.cpp"
# 1 "/app//"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "/app/example.cpp"
struct Int {
  int value;
};

__attribute__((noipa)) Int always_throws() { throw 123; }

void foo(Int &x) {
  try {
    x = always_throws();
  } catch (...) {
  }
}

int main() {
  Int x;
  x.value = 5;
  foo(x);
  return x.value;
}

[Bug ipa/111245] miscompilation: missing assignment when exception thrown

[briangreenery at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111245

--- Comment #1 from Brian Green <briangreenery at gmail dot com> ---
It seems working on gcc 11.4 or earlier, but broken since gcc 12.1 on all
versions I could test on godbolt.org.

[Bug ipa/111245] [12/13/14 Regression] miscompilation: missing assignment when exception thrown

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111245

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|miscompilation: missing     |[12/13/14 Regression]
                   |assignment when exception   |miscompilation: missing
                   |thrown                      |assignment when exception
                   |                            |thrown
      Known to work|                            |11.4.0
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Target Milestone|---                         |12.4
   Last reconfirmed|                            |2023-08-30

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.  I thought I saw another one almost the exact same but I can't find
it right now.

[Bug ipa/111245] [12/13/14 Regression] miscompilation: missing assignment when exception thrown

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111245

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r12-5244-g64f3e71c302b4a13e61656ee509e7050b9bce978

[Bug ipa/111245] [12/13/14 Regression] miscompilation: missing assignment when exception thrown since r12-5244-g64f3e71c302b4a13e61656ee509e7050b9bce978

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111245

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Sounds like call LHS analysis mistake in modref.