Clean up traces for symbolic values caching

thunder/core/symbol.py

@@ -340,7 +340,6 @@ def tag_tensorproxy_output_as_detached(proxy):
                 return proxy
 
             result = tree_map(tag_tensorproxy_output_as_detached, result)
-
         bsym = self.bind(*args, **kwargs, output=result, subsymbols=subsymbols)
         symbols_list = trace.peek_scope()
 
@@ -350,6 +349,12 @@ def tag_tensorproxy_output_as_detached(proxy):
             exception_type=AssertionError,
         )
 
+        # When using symbolic values, there may be duplicate prims.eq and prims.shape subsymbols that can be removed.
+        from thunder.core.transform_common import dce
+
+        subsymbols = dce(subsymbols, output=result)
+        bsym = bsym.from_bsym(subsymbols=subsymbols)
+
         symbols_list.append(bsym)
         return result
 

thunder/core/transform_common.py

@@ -142,20 +142,41 @@ def keep_or_swap(p):
 #   that only produce non-proxy objects
 # NOTE needed_proxies is an in/out argument, it takes an initial set of Variables you want to keep, and return
 #   all the needed proxies of the input trace
-def dce(trace: Trace, needed_proxies: None | set[Variable] = None) -> Trace:
+def dce(
+    trace_or_bsyms: Trace | list[BoundSymbolInterface],
+    needed_proxies: None | set[Variable] = None,
+    output: Any = None,
+) -> Trace | list[BoundSymbolInterface]:
+    """Runs a Dead Code Elimination (DCE) pass
+
+    Args:
+        trace_or_bsyms: The trace or list of bound symbols to run the DCE pass on.
+        needed_proxies: The set of variables to keep.
+        output: The output of the list of bound symbols.  This is only used if the input is a list of bound
+            symbols, and is required in that case
+
+    Returns:
+        The trace (if the input is a trace) or list of bound symbols (if the input is a list of bound symbols) after the DCE pass.
+    """
     start_time_ns = time.perf_counter_ns()
 
-    producer_map: ProxyDict = producers(trace)
+    producer_map: ProxyDict = producers(trace_or_bsyms)
 
-    flat_trace_outputs, _ = tree_flatten(trace.output)
+    if isinstance(trace_or_bsyms, Trace):
+        bound_symbols = trace_or_bsyms.bound_symbols
+        output = trace_or_bsyms.output
+    else:
+        bound_symbols = trace_or_bsyms
+
+    flat_trace_outputs, _ = tree_flatten(output)
     if needed_proxies is None:
         needed_proxies: set[Variable] = set(tuple(variableify(x) for x in flat_trace_outputs if isinstance(x, Proxy)))
     else:
         needed_proxies.update(tuple(variableify(x) for x in flat_trace_outputs if isinstance(x, Proxy)))
     dced = []
 
     bsym: BoundSymbol
-    for bsym in reversed(trace.bound_symbols):
+    for bsym in reversed(bound_symbols):
         # Preserves symbols that should never be collected
         if has_tags(bsym, {prims.OpTags.DONT_DCE}):
             needed = True
@@ -182,19 +203,24 @@ def dce(trace: Trace, needed_proxies: None | set[Variable] = None) -> Trace:
             for x in nbsym.flat_proxy_args:
                 needed_proxies.add(variableify(x))
 
-    dcetrace = from_trace(trace)
     dced_bound_symbols = list(reversed(dced))
     # duplicate number proxies happen with the symbolic shapes and are
     # not covered by the above (due to being in tuples?).
     dced_bound_symbols = remove_duplicate_number_proxies(dced_bound_symbols)
-    dcetrace.bound_symbols = dced_bound_symbols
 
+    if isinstance(trace_or_bsyms, Trace):
+        result = from_trace(trace_or_bsyms)
+        result.bound_symbols = dced_bound_symbols
+    else:
+        result = dced_bound_symbols
     end_time_ns = time.perf_counter_ns()
     elapsed_time_ns = end_time_ns - start_time_ns
     elapsed_time_millis = elapsed_time_ns // 1000000
-    dcetrace.set_provenance(TraceProvenance(f"Dead Code Elimination (took {elapsed_time_millis} milliseconds)"))
 
-    return dcetrace
+    if isinstance(trace_or_bsyms, Trace):
+        result.set_provenance(TraceProvenance(f"Dead Code Elimination (took {elapsed_time_millis} milliseconds)"))
+
+    return result
 
 
 #

thunder/dynamo/utils.py

@@ -244,20 +244,20 @@ def get_backed_value(s):
     return tuple(map(get_backed_value, vals))
 
 
-def get_proxy_inputs_from_node(node: torch.fx.Node) -> tuple[tuple, dict]:
+def get_proxy_inputs_from_node(node: torch.fx.Node, tracectx) -> tuple[tuple, dict]:
     """Creates proxy inputs from a torch.fx.Node for use with Thunder.
 
     This function generates proxy inputs for a given torch.fx.Node
 
     Args:
         node (torch.fx.Node): The FX graph node to create proxy inputs for.
+        tracectx (TraceCtx): The trace context to use to generate proxy inputs.
     """
     import thunder
-    from thunder.core.trace import TraceCtx
     from thunder.core.proxies import proxy
 
     # We need to be under trace context to generate proxies.
-    with thunder.core.trace.tracectx(TraceCtx()):
+    with thunder.core.trace.tracectx(tracectx):
 
         def make_input_proxy(arg_node):
             # This is a Node in the graph representing a Tensor or tuple of Tensors or
@@ -365,8 +365,10 @@ def _run_with_cache_info():
         cache_info["default_dtype"] = torch.get_default_dtype()
         cache_info["default_device"] = torch.get_default_device()
 
+        tracectx = TraceCtx()
+
         try:
-            proxy_args, proxy_kwargs = get_proxy_inputs_from_node(node)
+            proxy_args, proxy_kwargs = get_proxy_inputs_from_node(node, tracectx)
         except Exception as e:
             return False, SplitReason(
                 SplitReasonType.EXCEPTION_PROXY_THUNDER_OP,
@@ -380,7 +382,7 @@ def _run_with_cache_info():
             else thunder_symbol
         )
         # We need to be under trace context to generate proxies.
-        with thunder.core.trace.tracectx(TraceCtx()):
+        with thunder.core.trace.tracectx(tracectx):
             try:
                 function_to_run(*proxy_args, **proxy_kwargs)
             except Exception as e:
@@ -463,6 +465,7 @@ def is_node_supported_by_thunder(
     """
     Determine whether thunder can execute the operation described by this node.
     """
+    from thunder.core.trace import TraceCtx
     # Docs from the torch.fx.Node - https://pytorch.org/docs/stable/fx.html#torch.fx.Node
     # Each Node has a function specified by its op property
     # Below are the details for the ones this function is interested in -
@@ -534,7 +537,7 @@ def is_node_supported_by_thunder(
     if torchctx.has_method(node.target):
         # `torchctx.get_method` requires args and kwargs to resolve which overload of the method is picked.
         try:
-            args, kwargs = get_proxy_inputs_from_node(node)
+            args, kwargs = get_proxy_inputs_from_node(node, TraceCtx())
         except Exception as e:
             return False, SplitReason(
                 SplitReasonType.EXCEPTION_PROXY_THUNDER_OP,

thunder/executors/nvfuserex_impl.py

@@ -706,14 +706,11 @@ def has_cuda_input_or_output(self, bsym: BoundSymbol) -> bool:
         return False
 
     def _dce_bsyms(self, input_list, output, bsyms: list[BoundSymbol]) -> list[BoundSymbol]:
-        trace = TraceCtx(None)
-        trace.bound_symbols = bsyms
-        bsyms.append(prims.python_return.bind(output, output=None))
         needed_proxies: set[Variable] = set()
-        trace = dce(trace, needed_proxies)
+        bsyms = dce(bsyms, needed_proxies, output)
         # update the input_list by removing the unused inputs
         input_list[:] = [x for x in input_list if variableify(x) in needed_proxies]
-        return list(filter(lambda x: x.sym != prims.python_return, trace.bound_symbols))
+        return bsyms
 
     def fuse(self, region: Region, fusion_counter: int) -> BoundSymbol:
         sorted_unique_inputs: list[Proxy] = [unvariableify(x) for x in region.inputs]

thunder/tests/test_core.py

@@ -2170,6 +2170,36 @@ def func(x, y, device):
     assert [t.name for t in tree_flatten(flatten_cse_trace.output)[0]] == ["t4", "t4", "t6", "t14", "t15", "t16", "t17"]
 
 
+@instantiate(
+    dtypes=NOTHING,
+)
+def test_dce(executor, device, _):
+    def func(x):
+        dead_code = x + 1  # noqa: F841
+        y = x * x
+        return y
+
+    x = make_tensor((2, 2), device=device, dtype=torch.float32)
+    compiled = thunder.jit(func, executors=executor.executors_list())
+    compiled(x)
+    traces = thunder.last_traces(compiled)
+
+    # find last trace before DCE is applied
+    for i, trace in enumerate(traces):
+        provenance = trace.get_provenance().pss if trace.get_provenance() else ""
+        if "Dead Code Elimination" in provenance:
+            break
+    i -= 1
+    trace = traces[i]
+
+    from thunder.core.transform_common import dce
+
+    dced_trace = dce(trace)
+    dced_bsyms = dce(trace.bound_symbols)
+    assert len(dced_trace.bound_symbols) == len(trace.bound_symbols) - 1
+    assert len(dced_trace.bound_symbols) == len(dced_bsyms)
+
+
 def test_symbol_flat_args():
     from thunder.core.symbol import Symbol, BoundSymbol
 
@@ -3295,22 +3325,28 @@ def clean(tr):
 
 
 def test_prims_pack_list():
-    def foo():
-        pass
-
-    trace = TraceCtx(foo)
+    def foo(x):
+        a, b = x
+        return [a, b]
 
     a = torch.randn(2, 2)
     b = torch.randn(2, 2)
 
+    jfoo = thunder.jit(foo)
+    jfoo((a, b))
+
+    trace = thunder.last_traces(jfoo)[-1]
+
+    return_bsym = trace.bound_symbols[-1]
+    trace.bound_symbols = trace.bound_symbols[:-1]
+
     with tracectx(trace):
-        x = prims.unpack_trivial(a, name="x")
-        y = prims.unpack_trivial(b, name="y")
+        x, y = return_bsym.flat_args
         packed_list = prims.pack_list(x, y)
         prims.python_return(packed_list)
 
     func = trace.python_callable()
-    actual = func()
+    actual = func(a, b)
     expected = [a, b]
 
     assert isinstance(actual, list) and actual == expected