[llvm-bugs] [Bug 52577] New: Signaling NaNs are seem supported but __SUPPORT_SNAN__ is not defined

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52577

            Bug ID: 52577
           Summary: Signaling NaNs are seem supported but __SUPPORT_SNAN__
                    is not defined
           Product: clang
           Version: 13.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C
          Assignee: unassignedclangbugs at nondot.org
          Reporter: pavel.morozkin at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Note: this may not be a bug, but the subject needs a clarification.

This code:
#define _WANT_SNAN
#ifdef __SUPPORT_SNAN__
#pragma message "__SUPPORT_SNAN__ is defined"
#else
#pragma message "__SUPPORT_SNAN__ is not defined"
#endif

compiled with:
$ clang -std=c11 -pedantic -Wall -Wextra -ffp-model=strict -c

leads to:
<source>:5:9: warning: __SUPPORT_SNAN__ is not defined [-W#pragma-messages]

However, according to some tests signaling NaNs are supported.

Then what is the real reason to not define __SUPPORT_SNAN__?

It may be useful to mention the status of support of signaling NaNs in User's
Manual: https://clang.llvm.org/docs/UsersManual.html.

Version: clang 13.0.0 on x86_64 on Linux

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