Check out "Finding and Understanding Bugs in C Compilers": http://www.cs.utah.edu/~regehr/papers/pldi11-preprint.pdf.

The paper explains what-is-bug/what-causes-it/what-is-impact for selected bugs. Complete list of 282 compiler bugs found (79 GCC, 203 LLVM) is also available online: http://embed.cs.utah.edu/csmith/.