Program w. gcc-4.7.4 yields diff. res. at every run (res. not reproducible) since 28/3/19 --but earlier NOT. Why? W. other gcc versions (4.6.3 or 9.1.0) no such error.

I have been using gcc-4.7.4 for a long series of computations: solving large ODE systems using the CVODE integrator software. The results were completely reproducible and accurate. I finished those computations on the 9 March 2019. After a break, I restarted computations in April. 2019 Then I noticed that the results were irreproducible: at every run of excatly the same code with exactly the same input data, I obtained somewhat, but not wildly, different results, which varied apparently randomly. In the program code, no random numbers are generated, which could have caused such a result. To try to find out the reason for this error, I used two other versions of gcc: gcc-4.6.3 and gcc-9.1.0, which I have just freshly built. Both of the produced reproducible results with the same program code. Moreover the results produced by the two different versions were identical but were slightly different from the original results (obtained up to 9 March). My question is: how that could have happened?

Browsing the files related to gcc-4.7.4, I noticed that the directory
/usr/include/x86_64-linux-gnu was updated on Mar 28 17:56
and the directory
/usr/lib/x86_64-linux-gnu on Apr 11,
justr before the day when I started the computations again. The updates must have happened automatically, since i was not aware of them an certainly did not carry them out.

Here is, how gcc-4.7.4 was configured

~ $ /usr/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.7.4-3ubuntu12' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --enable-objc-gc --with-cloog --enable-cloog-backend=ppl --disable-cloog-version-check --disable-ppl-version-check --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.4 (Ubuntu/Linaro 4.7.4-3ubuntu12)

Ths Linux system I use is Linux Mint 18.3 (Sylvia)
uname -a
Linux tph-desk-502 4.13.0-45-generic #50~16.04.1-Ubuntu SMP Wed May 30 11:18:27 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

My aim is to get (somehow) the original and proper workings of the compiler gcc-4.7.4 restored. I would be grateful to you if you could help me in achieving this aim.

Dr. T.I. Toth
University of Cologne, Cologne, Germany