[Bug tree-optimization/18487] Warnings for pure and const functions that are not actually pure or const

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=18487

--- Comment #10 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
fizzbooze: you were asking on IRC about where the existing implementation is;
see gcc/ipa-pure-const.c - though I believe that merely covers tracking the
user-provided flags interprocedurally; I don't think it covers walking
individual stmts and detecting side-effects.