This may be a bit of a long post, but I'm trying to provide as much information as possible. I'm attempting to work on a minimalistic Clojure friendly VM. The bytecode is quite a bit like Python and the program I'm testing looks something like this: add-fn (make-code :bytecode [ADD RETURN] :vars [] :consts [] :locals 0 :stacksize 2) inner-code (make-code :bytecode [STORE_LOCAL 2 PUSH_CONST, 0, STORE_LOCAL, 0, NO_OP, ; 6 PUSH_LOCAL, 0, PUSH_LOCAL, 2, EQ, COND_JMP, 26, PUSH_LOCAL 0 PUSH_CONST 1 PUSH_CONST 2 INVOKE 2 STORE_LOCAL, 0, JMP, 6, NO_OP, ;21 PUSH_LOCAL, 0, RETURN] :vars [] :consts [0 1 add-fn] :stacksize 5 :locals 3) outer-code (make-code :bytecode [PUSH_CONST, 0, PUSH_CONST, 1, INVOKE, 1, RETURN] :vars [] :consts [100000, inner-code] :stacksize 2 :locals 0) This program simply increments a local from 0 to 100000. When I tested this using ADD in the inner-code, I ended up with a very tight trace. However, when I added, add-fn the frame for inner trace ends up getting half created at some points. The code for the main interpreter is here: https://bitbucket.org/halgari/clojure-vm/src/a95d278c7540cd16efb025f878c3773... I'm attaching a copy of my latest trace. The part I'm not happy with is at the end of the trace: debug_merge_point(0, 0, 'INVOKE 2') p64 = new_array(1, descr=<ArrayP 8>) +1165: p65 = call(ConstClass(ll_mul__GcArray_Ptr_GcStruct_objectLlT_arrayPtr_Signed), p64, 2, descr=<Callr 8 ri EF=4>) +1251: guard_no_exception(descr=<Guard0x1006f66b0>) [p0, p65, p60, p6, p8, p16, p18] +1299: setarrayitem_gc(p65, 0, p60, descr=<ArrayP 8>) +1338: setarrayitem_gc(p65, 1, ConstPtr(ptr37), descr=<ArrayP 8>) p67 = new_array(2, descr=<ArrayP 8>) +1446: setarrayitem_gc(p67, i30, p60, descr=<ArrayP 8>) +1451: p68 = getarrayitem_gc(p65, 1, descr=<ArrayP 8>) +1462: setarrayitem_gc(p67, i40, p68, descr=<ArrayP 8>) debug_merge_point(1, 1, 'ADD') +1474: p69 = getarrayitem_gc(p67, i48, descr=<ArrayP 8>) +1479: setarrayitem_gc(p67, i48, ConstPtr(null), descr=<ArrayP 8>) +1488: p70 = getarrayitem_gc(p67, i52, descr=<ArrayP 8>) +1500: setarrayitem_gc(p67, i52, ConstPtr(null), descr=<ArrayP 8>) +1509: i71 = getfield_gc(p69, descr=<FieldS clojure.vm.primitives.Integer.inst_int_value 8>) +1513: i72 = getfield_gc(p70, descr=<FieldS clojure.vm.primitives.Integer.inst_int_value 8>) +1517: i73 = int_add(i71, i72) p74 = new_with_vtable(4297160080) +1531: setfield_gc(p74, i73, descr=<FieldS clojure.vm.primitives.Integer.inst_int_value 8>) +1535: setarrayitem_gc(p67, i52, p74, descr=<ArrayP 8>) debug_merge_point(1, 1, 'RETURN') +1540: p75 = getarrayitem_gc(p67, i52, descr=<ArrayP 8>) +1545: setarrayitem_gc(p67, i52, ConstPtr(null), descr=<ArrayP 8>) debug_merge_point(0, 0, 'STORE_LOCAL 0') debug_merge_point(0, 0, 'JMP 6') debug_merge_point(0, 0, 'NO_OP') +1554: jump(p0, p75, p6, p8, p16, p18, i21, i30, i40, i48, i52, descr=TargetToken(4302274768)) I'm not sure why these allocations aren't getting removed. Any thoughts? Thanks, Timothy