Can compiler optimization introduce bugs?

Question

Today I had a discussion with a friend of mine and we debated for a couple of hours about \"compiler optimization\".

I defended the point that sometimes

Answer 1

Just one example: a few days ago, someone discovered that gcc 4.5 with the option -foptimize-sibling-calls (which is implied by -O2) produces an Emacs executable that segfaults on startup.

This has apparently been fixed since.