[Bug middle-end/64101] New: GCC considers that the erf math function does not set errno

[niva at niisi dot msk.ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64101

            Bug ID: 64101
           Summary: GCC considers that the erf math function does not set
                    errno
           Product: gcc
           Version: 4.7.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: niva at niisi dot msk.ru

Created attachment 34131
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34131&action=edit
The preprocessed source of the test program

We use a cross-conpiler configured as follows: 
/home/niva/src/gcc-4.7.4/configure --target=mips64-none-elf --enable-threads=no
--disable-shared --enable-long-long --enable-c99 --enable-languages=c
--enable-multilib --enable-symvers=gnu --disable-libmudflap --disable-libssp
--disable-libgcc_eh --with-newlib --with-dwarf2 --with-system-zlib
--enable-generated-files-in-srcdir --verbose --prefix=/home/niva/local
--enable-cpp

The following program (the preprocessed source is attached)

#include <assert.h>
#include <errno.h>
#include <math.h>

int main ()
{
   double res;
   errno = 0;
   res = erf (-1.2553634935946022721708238314E-308);
   assert (errno == ERANGE);
   return 0;
}

compiled as

  mips64-none-elf-gcc -O1 tst_erf.c

produces an assertion though we use a POSIX-compliant math
library and the erf function sets errno = ERANGE
according to erf description in POSIX Programmer's Manual.  

The test program works correctly (i.e. without the assertion)
if we compile it with -fno-builtin-erf.

Apparently GCC treats erf as a "clean" or "pure" function
(see gcc/builtins.def). IMHO this is not correct. 

ISO C 99 (see 7.12.8.1) does not state directly whether erf
may set errno. But in 7.12.1 (6) it is stated that
"If the result underflows, the function returns an
implementation-defined value whose magnitude is no greater than the smallest
normalized positive number in the specified type; if the integer expression
math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
value ERANGE is implementation-defined; if the integer expression
math_errhandling & MATH_ERREXCEPT is nonzero, whether the ‘‘underflow’’
floating-point exception is raised is implementation-defined."

In many Linux erf man pages we read that 
"These functions do not set errno". 

But there is a bug report
https://sourceware.org/bugzilla/show_bug.cgi?id=6785 :
"When erf() is given a subnormal argument, it raises an underflow exception. 
However errno is not set.  It should be set to ERANGE."