Someone

Original .ll:
; ModuleID = 'b'

define fastcc i32 @_Dmain() {
entry:
        ret i32 0
}

define i32 @main(i32, i8**, i8**) {
entry:
        %ret = call i32 @_Dmain( )              ; <i32> [#uses=1]
        ret i32 %ret
}

---------------------------------------------------------------

after 'opt -std-compile-opts':
; ModuleID = 'test/bopt.bc'

define fastcc i32 @_Dmain() {
entry:
        ret i32 0
}

define i32 @main(i32, i8**, i8**) {
entry:
        unreachable
}