[Bug c++/109686] New: Errorneous infinite loop detection (-Winfinite-recursion)

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109686

Bug ID: 109686
   Summary: Errorneous infinite loop detection
(-Winfinite-recursion)
   Product: gcc
   Version: 14.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: madhur4127 at gmail dot com
  Target Milestone: ---

This code: 

```
#define myassert(x) \
do { \
if (! (x) ) \
abort(); \
}  while (false)

static void recursive(int n) {
myassert(n > 0);
recursive(n - 1);
printf("%d\n", n);
}
```

should not result in infinite recursion. Assert fails for all non-positive
integers. For positive numbers it counts down to 0 and then fails.

This affect GCC12, GCC13 and trunk: https://compiler-explorer.com/z/57qrnzdEK

[Bug middle-end/107334] Incorrect "infinite recursion detected" warning if base case aborts

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107334

Madhur Chauhan  changed:

   What|Removed |Added

 CC||madhur4127 at gmail dot com

--- Comment #2 from Madhur Chauhan  ---
*** Bug 109686 has been marked as a duplicate of this bug. ***

[Bug middle-end/109686] Errorneous infinite loop detection (-Winfinite-recursion)

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109686

Madhur Chauhan  changed:

   What|Removed |Added

 Resolution|--- |DUPLICATE
 Status|UNCONFIRMED |RESOLVED

--- Comment #2 from Madhur Chauhan  ---
Yes it's a dupe. Sorry.

*** This bug has been marked as a duplicate of bug 107334 ***

[Bug middle-end/107334] Incorrect "infinite recursion detected" warning if base case aborts

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107334

--- Comment #3 from Madhur Chauhan  ---
I feel changing the warning text will still cause troubles for people using
-Werror. This forces to use ignore pragmas or disable this warning completely,
none of them are ideal.

Maybe disable warning in this case?

[Bug c++/110383] New: Missed optimiztion: Default operator== with trivial struct can be replaced with bcmp

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110383

Bug ID: 110383
   Summary: Missed optimiztion: Default operator== with trivial
struct can be replaced with bcmp
   Product: gcc
   Version: 14.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: madhur4127 at gmail dot com
  Target Milestone: ---

Godbolt: https://compiler-explorer.com/z/Gr8E5zfo5

Default operator== produces inefficient assembly where it checks for each data
member therefore having a lot of branches. Clang produces better assembly with
memcmp / bcmp.

I know its hard to generalize performance claims but in the worst case having 8
branches (one for each member), is not more efficient than a bcmp.

[Bug target/116414] New: Missed optimization: Branch elimination and memory writes

[madhur4127 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116414

Bug ID: 116414
   Summary: Missed optimization: Branch elimination and memory
writes
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: target
  Assignee: unassigned at gcc dot gnu.org
  Reporter: madhur4127 at gmail dot com
  Target Milestone: ---

Godbolt: https://godbolt.org/z/oKrGfh34z

Code:

```
#include 
#include 

std::optional x(uint16_t x) 
{ return x <= 1 ? std::nullopt : std::optional{x}; }
```

GCC trunk generates a branch and uses memory writes whereas it could just use
`eax` like clang

```
x(unsigned short):
cmp di, 1
jbe .L5
mov WORD PTR [rsp-4], di
mov BYTE PTR [rsp-2], 1
mov eax, DWORD PTR [rsp-4]
ret
.L5:
mov BYTE PTR [rsp-2], 0
mov eax, DWORD PTR [rsp-4]
ret
```

clang:
```
x(unsigned short):
xor eax, eax
cmp di, 2
setae   al
shl eax, 16
or  eax, edi
ret
```