Revert [CodeGen] Do the Simple Early Return in block-placement pass to optimize the blocks

This reverts r368997 (git commit 2a903c0b)

It looks like this commit adds invalid predecessors to MBBs. The example
below fails the verifier after MachineBlockPlacement (run llc
-verify-machineinstrs):

@global.4 = external constant i8*

declare i32 @zot(...)

define i16* @snork.67() personality i8* bitcast (i32 (...)* @zot to i8*) {
bb:
  invoke void undef()
          to label %bb5 unwind label %bb4

bb4:                                              ; preds = %bb
  %tmp = landingpad { i8*, i32 }
          catch i8* null
  unreachable

bb5:                                              ; preds = %bb
  %tmp6 = load i32, i32* null, align 4
  %tmp7 = icmp eq i32 %tmp6, 0
  br i1 %tmp7, label %bb14, label %bb8

bb8:                                              ; preds = %bb11, %bb5
  invoke void undef()
          to label %bb9 unwind label %bb11

bb9:                                              ; preds = %bb8
  %tmp10 = invoke i16* undef()
          to label %bb14 unwind label %bb11

bb11:                                             ; preds = %bb9, %bb8
  %tmp12 = landingpad { i8*, i32 }
          cleanup
          catch i8* bitcast (i8** @global.4 to i8*)
  %tmp13 = icmp ult i64 undef, undef
  br i1 %tmp13, label %bb8, label %bb14

bb14:                                             ; preds = %bb11, %bb9, %bb5
  %tmp15 = phi i16* [ null, %bb5 ], [ null, %bb11 ], [ %tmp10, %bb9 ]
  ret i16* %tmp15
}

llvm-svn: 369104