Reviewers: Kevin Millikin, fschneider,
Message:
In theory, this should improve some benchmarks, and have at least no
negative
effects on others, but measurements show no real conclusive results. :-(
I just wanted to upload my changes to see if somebody sees a stupid mistake
or
some misconception how things work...
Description:
Give uses within a loop a greater weight when doing representation
inference.
Uses of a value are weighted by a factor of FLAG_loop_weight (default: 10)
for
every loop they are in. This makes uses in inner loops "more important",
which
should improve the result of the representation inference.
Please review this at http://codereview.chromium.org/8277031/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/flag-definitions.h
M src/hydrogen-instructions.h
M src/hydrogen-instructions.cc
M src/hydrogen.cc
Index: src/flag-definitions.h
===================================================================
--- src/flag-definitions.h (revision 9619)
+++ src/flag-definitions.h (working copy)
@@ -152,6 +152,7 @@
DEFINE_bool(trace_osr, false, "trace on-stack replacement")
DEFINE_int(stress_runs, 0, "number of stress runs")
DEFINE_bool(optimize_closures, true, "optimize closures")
+DEFINE_int(loop_weight, 10, "loop weight for representation inference")
// assembler-ia32.cc / assembler-arm.cc / assembler-x64.cc
DEFINE_bool(debug_code, false,
Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc (revision 9619)
+++ src/hydrogen-instructions.cc (working copy)
@@ -67,6 +67,19 @@
}
+template<class T> inline const T& min(const T& a, const T& b) {
+ return (a < b) ? a : b;
+}
+
+
+int HValue::LoopWeight() const {
+ const int w = FLAG_loop_weight;
+ static const int weights[] = { 1, w, w*w, w*w*w, w*w*w*w };
+ return weights[min(block()->LoopNestingDepth(),
+ static_cast<int>(ARRAY_SIZE(weights)-1))];
+}
+
+
void HValue::AssumeRepresentation(Representation r) {
if (CheckFlag(kFlexibleRepresentation)) {
ChangeRepresentation(r);
@@ -1117,7 +1130,7 @@
HValue* value = it.value();
if (!value->IsPhi()) {
Representation rep = value->RequiredInputRepresentation(it.index());
- ++non_phi_uses_[rep.kind()];
+ non_phi_uses_[rep.kind()] += value->LoopWeight();
}
}
}
Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h (revision 9619)
+++ src/hydrogen-instructions.h (working copy)
@@ -556,6 +556,7 @@
HBasicBlock* block() const { return block_; }
void SetBlock(HBasicBlock* block);
+ int LoopWeight() const;
int id() const { return id_; }
void set_id(int id) { id_ = id; }
Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc (revision 9619)
+++ src/hydrogen.cc (working copy)
@@ -1652,7 +1652,7 @@
Representation rep = use->RequiredInputRepresentation(it.index());
if (rep.IsNone()) continue;
if (use->IsPhi()) HPhi::cast(use)->AddIndirectUsesTo(&use_count[0]);
- ++use_count[rep.kind()];
+ use_count[rep.kind()] += use->LoopWeight();
}
int tagged_count = use_count[Representation::kTagged];
int double_count = use_count[Representation::kDouble];
--
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