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OptimizeInstructions: Optimize subsequent struct.sets after struct.new_with_default #6523

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Apr 23, 2024
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OptimizeInstructions: Optimize subsequent struct.sets after struct.new_with_default #6523

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33 changes: 21 additions & 12 deletions src/passes/OptimizeInstructions.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1931,12 +1931,6 @@ struct OptimizeInstructions
return false;
}

if (new_->isWithDefault()) {
// Ignore a new_default for now. If the fields are defaultable then we
// could add them, in principle, but that might increase code size.
return false;
}

auto index = set->index;
auto& operands = new_->operands;

Expand All @@ -1953,20 +1947,35 @@ struct OptimizeInstructions
}

// We must move the set's value past indexes greater than it (Y and Z in
// the example in the comment on this function).
// the example in the comment on this function). If this is not with_default
// then we must check for effects.
// TODO When this function is called repeatedly in a sequence this can
// become quadratic - perhaps we should memoize (though, struct sizes
// tend to not be ridiculously large).
for (Index i = index + 1; i < operands.size(); i++) {
auto operandEffects = effects(operands[i]);
if (operandEffects.invalidates(setValueEffects)) {
// TODO: we could use locals to reorder everything
return false;
if (!new_->isWithDefault()) {
for (Index i = index + 1; i < operands.size(); i++) {
auto operandEffects = effects(operands[i]);
if (operandEffects.invalidates(setValueEffects)) {
// TODO: we could use locals to reorder everything
return false;
}
}
}

// We can optimize here!
Builder builder(*getModule());

// If this was with_default then we add default values now. That does
// increase code size in some cases (if there are many values, and few sets
// that get removed), but in general this optimization is worth it.
if (new_->isWithDefault()) {
auto& fields = new_->type.getHeapType().getStruct().fields;
for (auto& field : fields) {
auto zero = Literal::makeZero(field.type);
operands.push_back(builder.makeConstantExpression(zero));
}
}

// See if we need to keep the old value.
if (effects(operands[index]).hasUnremovableSideEffects()) {
operands[index] =
Expand Down
30 changes: 22 additions & 8 deletions test/lit/passes/optimize-instructions-gc-heap.wast
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Expand Up @@ -9,10 +9,11 @@
;; CHECK: (type $struct (struct (field (mut i32))))
(type $struct (struct (field (mut i32))))

;; CHECK: (type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))

;; CHECK: (type $struct2 (struct (field (mut i32)) (field (mut i32))))
(type $struct2 (struct (field (mut i32)) (field (mut i32))))

;; CHECK: (type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))
(type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))

;; CHECK: (func $tee (type $1)
Expand Down Expand Up @@ -575,22 +576,35 @@

;; CHECK: (func $default (type $1)
;; CHECK-NEXT: (local $ref (ref null $struct))
;; CHECK-NEXT: (struct.set $struct 0
;; CHECK-NEXT: (local.tee $ref
;; CHECK-NEXT: (struct.new_default $struct)
;; CHECK-NEXT: (local $ref3 (ref null $struct3))
;; CHECK-NEXT: (local.set $ref
;; CHECK-NEXT: (struct.new $struct
;; CHECK-NEXT: (i32.const 10)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $ref3
;; CHECK-NEXT: (struct.new $struct3
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: (i32.const 33)
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 20)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $default
(local $ref (ref null $struct))
(local $ref3 (ref null $struct3))
;; We optimize new_default as well, adding default values as needed.
(struct.set $struct 0
(local.tee $ref
;; Ignore a new_default for now. If the fields are defaultable then we
;; could add them, in principle, but that might increase code size.
(struct.new_default $struct)
)
(i32.const 20)
(i32.const 10)
)
(struct.set $struct3 1
(local.tee $ref3
(struct.new_default $struct3)
)
(i32.const 33)
)
)

Expand Down
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