I saw this topic for the visual Fortran compiler for Windows, I get the same warning on OSX for a code that I didn't write.
#6375: Because of COMMON, the alignment of object is inconsistent with its type
What does it mean? what are the "potential performance impact"?
For example, you might have an odd number of 32 bit data followed by 64 bit data. That could result in a data access requiring references to 2 cache lines and the hardware piecing the 2 together or splitting them, which may be slow even though you probably have a hardware platform which supports it.
Isn't there a preferred practice, when using COMMON, to list variables largest first, e.g., 64-bit, then in decreasing order of size? Of course, you need to change all references to the common block.