[Bug libstdc++/63780] New: std::remquo returns wrong quotient

[charles at karney dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63780

            Bug ID: 63780
           Summary: std::remquo returns wrong quotient
           Product: gcc
           Version: 4.8.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: charles at karney dot com

Created attachment 33921
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33921&action=edit
intermediate output from compiler

This code:

#include <cmath>
#include <iostream>

int main() {
  int n;
  double x = 3419, m = 360;
  double y = std::remainder(x, m);
  double z = std::remquo(x, m, &n);
  std::cout << "result " << y << " " << z << " " << n << "\n";
}

compiled with

g++ --std=c++11 -O0 -o remquo-bug remquo-bug.cpp && ./remquo-bug

produces

result 179 539 8

The correct output is produced by -O1

result 179 179 9

Here is the output from g++ -v

Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.3/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-isl=/builddir/build/BUILD/gcc-4.8.3-20140911/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.3-20140911/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.3 20140911 (Red Hat 4.8.3-7) (GCC) 

Output from -save-temps attached