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

[briangreenery at gmail dot com via Gcc-bugs]

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;
}