-Wfloat-equal does not catch comparision with constant value

[Quuxplusone]

Bugzilla Link	PR38331
Status	NEW
Importance	P enhancement
Reported by	David Bolvansky (david.bolvansky@gmail.com)
Reported on	2018-07-26 10:51:56 -0700
Last modified on	2021-04-15 22:30:43 -0700
Version	trunk
Hardware	PC Linux
CC	andrew.v.tischenko@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, tdiff@yandex.ru
Fixed by commit(s)
Attachments
Blocks
Blocked by
See also

Code compiled with -Wfloat-equal:
bool compare (const float lhs, const float rhs)
{
  return lhs == rhs; // Clang warns
}

bool compare2 (const float lhs, const float rhs)
{
  return lhs == 1.0; // No warning from Clang, GCC warns
}

[Quuxplusone]

Ok, I checked the code and I see this is disabled by default.

https://github.com/llvm-mirror/clang/blob/2100b0595fd952fab745d8f53e6619ca0c0d06b2/lib/Sema/SemaChecking.cpp#L8104

Maybe we can reconsider that special case?

Or if you are disagree to turn it on for constants - maybe we could add "-
Wfloat-equal-constant" (or similar name) to handle this case (off by default)?

[Quuxplusone]

However the same warning is produced if the constant was specified as an
integer:

double f(double x)
{
    return x == 0 ? x : -x;
}

<source>:3:14: warning: comparing floating point with == or != is unsafe [-
Wfloat-equal]
    return x == 0 ? x : -x;