[Bug c++/113852] -Wsign-compare doesn't warn on unsigned result types

[admin at computerquip dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113852

--- Comment #7 from Zachary L  ---
(In reply to Richard Biener from comment #6)
> Well, given athat a1 * a2 is carried out in 'int' you are invoking undefined
> behavior if it overflows.  GCC assumes that doesn't happen so it's correct
> to elide the diagnostic.  Unless you make overflow well-defined with -fwrapv.
> 
> I think that errors on the right side for the purpose of -Wsign-compare.

Removing a diagnostic because the program could be ill-formed seems backwards
to me, especially since it seems like there's already logic in performing this
diagnostic. Perhaps I've misunderstood the situation?

[Bug c++/113852] -Wsign-compare doesn't warn on unsigned result types

[admin at computerquip dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113852

--- Comment #1 from Zachary L  ---
Sorry, that should say "If *both* a1 or a2 are constexpr, the warning will
occur."

[Bug c++/113852] New: -Wsign-compare doesn't warn on unsigned result types

[admin at computerquip dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113852

Bug ID: 113852
   Summary: -Wsign-compare doesn't warn on unsigned result types
   Product: gcc
   Version: 14.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: admin at computerquip dot com
  Target Milestone: ---

I haven't quite figured out the pattern here so the title may not be great.
Some code may help explain better: https://godbolt.org/z/d8cqd1WqP

```
#include 
#include 
#include 

int main()
{
uint16_t a1 = std::numeric_limits::max();
uint16_t a2 = std::numeric_limits::max();

/* a1 * a2 should be 4294836225 in math terms */
uint64_t a3 = 4294836225;

/*
 * The result of (a1 * a2) is of type int and the result is negative.
 * (a1 * a2) ends up as some bogus high number because the common
 * type here ends up as uint64_t and sign-extension occurs.
 */
if ((a1 * a2) > a3) {
std::cout << "this will print\n";
}
}
```

Some observations I've noticed:
* If either a1 or a2 are constexpr, the warning will occur.
* This used to warn up until 8.1.
* Clang also doesn't warn here but MSVC will with /W3 or higher.
* This seems like a slight variation of
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101645

[Bug libstdc++/111145] New: istream::operator>>(streambuf*) does not set gcount

[admin at computerquip dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45

Bug ID: 45
   Summary: istream::operator>>(streambuf*) does not set gcount
   Product: gcc
   Version: 13.2.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: libstdc++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: admin at computerquip dot com
  Target Milestone: ---

Example code: https://godbolt.org/z/cW9Pe1c85
```
#include 
#include 

int main()
{
std::ostringstream oss;
std::istringstream iss("test");

iss >> oss.rdbuf();

std::cout << "gcount is " << iss.gcount() << "\n";
}
```

Here I'm expecting `iss.gcount()` to return 4 as `iss >> oss.rdbuf();`, as far
as I can tell, fits under the conditions that should set the value accessed by
gcount().

As per the godbolt link, it instead returns 0.