[Bug c++/77832] New: isnan() check causes signal 8 with signaling nans

[gmc at synopsys dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77832

            Bug ID: 77832
           Summary: isnan() check causes signal 8 with signaling nans
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gmc at synopsys dot com
  Target Milestone: ---

Created attachment 39741
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39741&action=edit
test program

The example prog shows incorrect isnan() behavior when used with signaling
NaNs. (isnan() itself should not generate a signal AFAIK)

Run the test prog is run with a SINGLE argument(0 => use quiet Nan ; 1 => use
signaling Nan):
 - quite NaNs behave as expected
 - for signaling NaNs:
     - the optimized exe behaves correctly and does NOT trigger a signal
     - the debug exe gets signal 8 on the isnan()

If you then run the exact same program with an additional arg (any old value)
then the optimized exe will now ALSO trigger a signal on isnan() .

Attachment 'run' runs the test prog in each of these variants - none are
expected to signal.

OS: RedHat 6.6
Works with GCC version 5.4 
Does not work on GCC versions 6.1 and 6.
Compiler is built as follows:
$ g++ -v
Using built-in specs.
COLLECT_GCC=/remote/sweifs/PST/gmc/Gnu/GCC_6.2.0/bin/g++
COLLECT_LTO_WRAPPER=/remote/sweifs/PST/gmc/Gnu/GCC_6.2.0/libexec/gcc/x86_64-redhat-linux/6.2.0/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../src/gcc-6.2.0/configure
--prefix=/remote/sweifs/PST/gmc/Gnu/GCC_6.2.0 --enable-bootstrap
--enable-threads=posix --disable-checking --with-system-zlib
--enable-__cxa_atexit --disable-libunwind-exceptions
--enable-languages=c,c++,fortran --disable-libgcj --with-cpu=generic
--build=x86_64-redhat-linux
Thread model: posix
gcc version 6.2.0 (GCC)