[Bug c++/109281] New: use std::optional results in suboptimal code

[Bug c++/109281] New: use std::optional results in suboptimal code

[vincenzo.innocente at cern dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109281

            Bug ID: 109281
           Summary: use std::optional results in suboptimal code
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincenzo.innocente at cern dot ch
  Target Milestone: ---

In the following (almost real) code gcc emits suboptimal code if std::optional
is used w/r/t home made one and clang

see https://godbolt.org/z/Pba51Ye7Y


-----

code


#include <optional>

// #define USE_OPTIONAL

#ifdef USE_OPTIONAL
struct SubRingCrossings {
  SubRingCrossings(int ci, int ni, float nd) : closestIndex(ci), nextIndex(ni),
nextDistance(nd) {}

  int closestIndex;
  int nextIndex;
  float nextDistance;
};
#else
struct SubRingCrossings {
  SubRingCrossings() : valid(false) {}
  SubRingCrossings(int ci, int ni, float nd) : valid(true), closestIndex(ci),
nextIndex(ni), nextDistance(nd) {}

  bool valid;
  int closestIndex;
  int nextIndex;
  float nextDistance;
};
#endif

bool condition();

#ifdef USE_OPTIONAL
std::optional<SubRingCrossings> foo() {
    if (condition()) {
        return std::nullopt;
    }
    return SubRingCrossings(1, 2, 3.14);
}
#else
SubRingCrossings foo() {
    if (condition()) {
        return SubRingCrossings();
    }
    return SubRingCrossings(1, 2, 3.14);
}
#endif

int bar() {
    auto tmp = foo();
#ifdef USE_OPTIONAL
    if (tmp) {
        return tmp->closestIndex;
#else
    if (tmp.valid) {
        return tmp.closestIndex;
#endif
    } else {
        return 0;
    }
}

[Bug tree-optimization/109281] use std::optional results in suboptimal code

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109281

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |101326, 95405

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is same as PR 95405 and PR 101326


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95405
[Bug 95405] Unnecessary stores with std::optional
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101326
[Bug 101326] std::optional returns forced through stack

[Bug tree-optimization/109281] use std::optional results in suboptimal code

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109281

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug tree-optimization/109281] use std::optional results in suboptimal code

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109281
Bug 109281 depends on bug 101326, which changed state.

Bug 101326 Summary: std::optional returns forced through stack
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101326

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

[Bug tree-optimization/109281] use std::optional results in suboptimal code

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109281

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup.

*** This bug has been marked as a duplicate of bug 95405 ***