[Bug c++/64141] New: Add option, -Wextra-copy

[r.p.nicholl at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64141

Bug ID: 64141
   Summary: Add option, -Wextra-copy
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: enhancement
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: r.p.nicholl at gmail dot com

I am suggesting to add -Wextra-copy. When you copy from a value in local scope
which is not accessed again afterwards, then this warning is triggered.


So for example:

extern std::string bar();
extern void foo(std::string);

int main()
{
  std::string s = bar();
  foo(s);
  return 0;
}

This would cause a warning at the call to foo(s), because it could be replaced
with a move-call in most cases.

[Bug c++/64142] New: Add option, -felide-copies

[r.p.nicholl at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64142

Bug ID: 64142
   Summary: Add option, -felide-copies
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: enhancement
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: r.p.nicholl at gmail dot com

See also https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64141

Very simply, when you copy from a value, and the compiler can prove that this
is the last use of the value before it goes out of scope, then the compiler
should change this to a move operation.

[Bug c++/64142] Add option, -felide-copies

[r.p.nicholl at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64142

--- Comment #1 from Ryan Nicholl  ---
The option would be -felide-copies, incase the title needs to be changed later.

[Bug other/64143] New: Add option -felide-aliases

[r.p.nicholl at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64143

Bug ID: 64143
   Summary: Add option -felide-aliases
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: enhancement
  Priority: P3
 Component: other
  Assignee: unassigned at gcc dot gnu.org
  Reporter: r.p.nicholl at gmail dot com

I am suggesting to add the option -felide-aliases.

For certian functions, perhaps those marked "hot", where the compiler can
determine the widths of access of any pointers used, the compiler would check
on entry, if certian pointers alias eachother or not, and then choose between
multiple overloads of the function depending on if this pointer aliasing
occured.

So for example, when multiplying to matricies and putting the results in an
index, if this optimization was enabled, on entry, it would check if the result
and the other arguments overlap or not. Then it would jump to the correct
function depending of the result of that check.

It is also possible, during profiling, that the compiler may check which types
of aliasing are more common, such as the case where the two inputs overlap
commonly, but it is unlikey for the inputs to overlap with the output.