[llvm-bugs] [Bug 39738] New: Passing double to isnan() triggers -Wconversion

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Nov 21 00:04:54 PST 2018


            Bug ID: 39738
           Summary: Passing double to isnan() triggers -Wconversion
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: sylvestre at debian.org
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Given this simple program:

-- >8 --
#include <math.h>

int main(void)
    double f = 2.0;

    if (isnan(f))
      return 1;

    return 0;
-- >8 --

we get conversion warnings when using clang, but not gcc.  This is
particularly annoying when trying to keep a project warning free and
using -Werror.

$ clang -Wconversion -o foo foo.c
foo.c:7:12: warning: implicit conversion loses floating-point precision:
'double' to 'float' [-Wconversion]
        if (isnan(f))
/usr/include/math.h:644:46: note: expanded from macro 'isnan'
#  define isnan(x) __MATH_TG ((x), __isnan, (x))
/usr/include/math.h:559:16: note: expanded from macro '__MATH_TG'
   ? FUNC ## f ARGS                             \
     ~~~~~~~~~ ^~~~
1 warning generated.

$ gcc -Wconversion -o foo foo.c

reported https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914201

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