Author: Armin Rigo <[email protected]>
Branch: shadowstack-perf
Changeset: r45262:745670afcd4d
Date: 2011-07-02 12:47 +0200
http://bitbucket.org/pypy/pypy/changeset/745670afcd4d/
Log: Avoid useless stores. Not really unit-tested :-/ At least it seems
that test_transformed_gc passes.
diff --git a/pypy/rpython/memory/gctransform/framework.py
b/pypy/rpython/memory/gctransform/framework.py
--- a/pypy/rpython/memory/gctransform/framework.py
+++ b/pypy/rpython/memory/gctransform/framework.py
@@ -188,6 +188,7 @@
gcdata.set_query_functions(gcdata.gc)
gcdata.gc.set_root_walker(root_walker)
self.num_pushs = 0
+ self.num_raw_store_avoided = 0
self.write_barrier_calls = 0
self.write_barrier_from_array_calls = 0
@@ -570,6 +571,9 @@
log.info("assigned %s typeids" % (len(group.members), ))
log.info("added %s push/pop stack root instructions" % (
self.num_pushs, ))
+ if self.num_raw_store_avoided:
+ log.info("avoided %s repeated raw_stores" % (
+ self.num_raw_store_avoided,))
if self.write_barrier_ptr:
log.info("inserted %s write barrier calls" % (
self.write_barrier_calls, ))
diff --git a/pypy/rpython/memory/gctransform/shadowstack.py
b/pypy/rpython/memory/gctransform/shadowstack.py
--- a/pypy/rpython/memory/gctransform/shadowstack.py
+++ b/pypy/rpython/memory/gctransform/shadowstack.py
@@ -7,7 +7,7 @@
from pypy.tool.algo.regalloc import perform_register_allocation
from pypy.translator.backendopt.ssa import DataFlowFamilyBuilder
from pypy.translator.unsimplify import copyvar
-from pypy.objspace.flow.model import Block, Link, checkgraph
+from pypy.objspace.flow.model import Block, Link, checkgraph, mkentrymap
class ShadowStackRootWalker(BaseRootWalker):
@@ -252,7 +252,7 @@
# Compute the set of "useless stores", i.e. the Variables in the
# gc_push_roots that are storing the same value as the one previously
# loaded from the same index.
- #useless_stores = self.compute_useless_stores(graph)
+ useless_stores = self.compute_useless_stores(gct, graph, spans)
#
# Put at the start of the graph: "incr_stack(); fill with zeroes"
llops = LowLevelOpList()
@@ -299,7 +299,9 @@
assert -numcolors <= k < 0
c_k = rmodel.inputconst(lltype.Signed, k)
if op.opname == "gc_push_roots":
- llops.genop("raw_store", [top_addr, c_type, c_k, v])
+ if (block, op, v) not in useless_stores:
+ llops.genop("raw_store", [top_addr, c_type,
+ c_k, v])
else:
v_newaddr = llops.genop("raw_load",
[top_addr, c_type, c_k],
@@ -308,3 +310,56 @@
block.operations[:] = llops
#
checkgraph(graph)
+
+
+ def compute_useless_stores(self, gct, graph, spans):
+ # A "useless store" is a Variable in a gc_push_roots instruction
+ # that is the "same" one, in all paths, as the one loaded by a
+ # previous gc_pop_roots. Two variables v and w are the "same"
+ # if spans.find_rep(v) is spans.find_rep(w).
+ entrymap = mkentrymap(graph)
+ #
+ def enumerate_previous_gc_pop_roots(block, index):
+ result = []
+ seen = set()
+ pending = [(block, index)]
+ while pending:
+ block, index = pending.pop()
+ for i in range(index-1, -1, -1):
+ if block.operations[i].opname == 'gc_pop_roots':
+ # found gc_pop_roots, record it and stop
+ result.append(block.operations[i])
+ break
+ else:
+ # find all blocks that go into this one
+ if block is graph.startblock:
+ return None
+ for link in entrymap[block]:
+ prevblock = link.prevblock
+ if prevblock in seen:
+ continue
+ seen.add(prevblock)
+ pending.append((prevblock, len(prevblock.operations)))
+ return result
+ #
+ useless = {}
+ for block in graph.iterblocks():
+ for i, op in enumerate(block.operations):
+ if op.opname == 'gc_push_roots':
+ result = enumerate_previous_gc_pop_roots(block, i)
+ if not result:
+ continue
+ for original_v in op.args:
+ v = spans.find_rep(original_v)
+ # check if 'v' is in all prevop.args
+ for prevop in result:
+ for w in prevop.args:
+ if spans.find_rep(w) is v:
+ break # found 'v' in this prevop.args
+ else:
+ break # did not find 'v' in this prevop.args
+ else:
+ # yes, found 'v' in each prevop.args -> useless
+ useless[block, op, original_v] = True
+ gct.num_raw_store_avoided += 1
+ return useless
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