Possible C compiler bug

Hello everyone, the attached test program gives wrong results when compiled with -O1 using the compiler versions 12.1.1, 12.1.6, 13.1.3, or 14.0.1 while it produces the expected results with gcc 4.4.7. The code was distilled from a physics simulation that does a lot of matrix operations. In this test program, a pointer to a nested structure of doubles is passed to a function that modifies these doubles. It seems the wrong operands are used here.