[Valgrind-developers] small ir_opt.c tweak

[Florian K. <br...@ac...>]

In fold_Expr use a switch instead of an if-chain for clarity and
efficiency. Previously, the code would test a Unop node with a
non-constant subtree for being a Binop and Mux0X. Likewise all Binop
nodes would subsequently be tested for being a Mux0X.
The attached patch fixes that. In favour of having a small patch I did
not re-indent the code.  OK?  Regtested on x86 and x86_64.

   Florian