[pypy-dev] Virtualizable Frames getting half removed in trace

[Timothy Baldridge]

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/a95d278c7540cd16efb025f878c3773c2c494807/clojure/vm/interpreter.py?at=master#cl-169

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
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