[sledge] Name trampoline blocks using source block instead of instr

Summary:
The source block name is normally visible in the LLAIR code, while the
name of e.g. a branch instruction is some internal number. This change
only makes the output LLAIR code slightly easier to read.

Reviewed By: jvillard

Differential Revision: D26250521

fbshipit-source-id: 4723a58f7

sledge/cli/frontend.ml

@@ -903,7 +903,8 @@ let xlate_jump :
       let mov =
         Inst.move ~reg_exps:(IArray.of_list_rev rev_reg_exps) ~loc
       in
-      let lbl = find_name instr ^ ".jmp." ^ dst_lbl in
+      let src_lbl = label_of_block (Llvm.instr_parent instr) in
+      let lbl = src_lbl ^ ".jmp." ^ dst_lbl in
       let blk =
         Block.mk ~lbl
           ~cmnd:(IArray.of_array [|mov|])