Auto merge of #29757 - dotdash:mir_simplify_cfg, r=nikomatsakis

For now, this pass does some easy transformations, like eliminating
empty blocks that just jump to another block, some trivial
conversion of If terminators into Gotos and removal of dead blocks.

r? @nikomatsakis

diff --cc src/librustc_mir/mir_map.rs
index 9362aeb6005c148757f4df155a0e8dc1e3a2dda1,1e488ceedfd883e25463d13bb2eb24049ed6e271..1359cbc82a662541f84bb4d70b8d2f5467a195e6
--- 1/src/librustc_mir/mir_map.rs
--- 2/src/librustc_mir/mir_map.rs
+++ b/src/librustc_mir/mir_map.rs
@@@ -22,8 -22,9 +22,9 @@@ extern crate rustc_front
  
  use build;
  use dot;
+ use transform::*;
  use repr::Mir;
 -use hair::cx::{PatNode, Cx};
 +use hair::cx::Cx;
  use std::fs::File;
  
  use self::rustc::middle::infer;

diff --cc src/librustc_mir/repr.rs
Simple merge