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feat: optimize the active init operation of zero-initialized memory of makeFieldInitializationInConstructor #2948

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feat: optimize the active init operation of zero-initialized memory of makeFieldInitializationInConstructor #2948

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15422ca
test
KKiiim Sep 17, 2025
d5c8c0d
fix
KKiiim Sep 17, 2025
1f042c6
fix
KKiiim Sep 17, 2025
e82e45f
fix
KKiiim Sep 18, 2025
f0237f5
fix
KKiiim Oct 4, 2025
69d3d89
fix test
KKiiim Oct 4, 2025
7edbea2
Merge branch 'AssemblyScript:main' into opt-zero-init
KKiiim Oct 4, 2025
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1 change: 1 addition & 0 deletions NOTICE
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ under the licensing terms detailed in LICENSE:
* Fabián Heredia Montiel <[email protected]>
* Jonas Minnberg <[email protected]>
* Kam Chehresa <[email protected]>
* Rui Jin <[email protected]>

Portions of this software are derived from third-party works licensed under
the following terms:
Expand Down
39 changes: 29 additions & 10 deletions src/compiler.ts
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Expand Up @@ -59,7 +59,8 @@ import {
isConstExpressionNaN,
ensureType,
createType,
getConstValueInteger
getConstValueInteger,
isConstZero
} from "./module";

import {
Expand Down Expand Up @@ -10025,6 +10026,14 @@ export class Compiler extends DiagnosticEmitter {

// === Specialized code generation ==============================================================

/** Check if possible to optimize the active initialization away if it's zero */
canOptimizeZeroInitialization(valueExpr: ExpressionRef): bool {
if ((this.options.runtime != Runtime.Incremental) && (this.options.runtime != Runtime.Stub)) {
return false;
}
return isConstZero(valueExpr);
}

/** Makes a constant zero of the specified type. */
makeZero(type: Type): ExpressionRef {
let module = this.module;
Expand Down Expand Up @@ -10372,6 +10381,7 @@ export class Compiler extends DiagnosticEmitter {
let parameterIndex = fieldPrototype.parameterIndex;

// Defer non-parameter fields until parameter fields are initialized
// Since non-parameter may depend on parameter fields
if (parameterIndex < 0) {
if (!nonParameterFields) nonParameterFields = new Array();
nonParameterFields.push(property);
Expand Down Expand Up @@ -10407,16 +10417,25 @@ export class Compiler extends DiagnosticEmitter {
let initializerNode = fieldPrototype.initializerNode;
assert(fieldPrototype.parameterIndex < 0);
let setterInstance = assert(field.setterInstance);
let expr = this.makeCallDirect(setterInstance, [
module.local_get(thisLocalIndex, sizeTypeRef),
initializerNode // use initializer if present, otherwise initialize with zero
? this.compileExpression(initializerNode, fieldType, Constraints.ConvImplicit)
: this.makeZero(fieldType)
], field.identifierNode, true);
if (this.currentType != Type.void) { // in case
expr = module.drop(expr);

if (initializerNode) {
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If there isn't an initializerNode, this code neglects to zero-initialize the field when stub runtime is used (and the stub runtime doesn't zero-initialize allocated memory!). The previous code's this.makeZero(fieldType) happened to cover this case.

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Looks no need to zero-initialize because:

  1. memory will not be collected and reused in stub runtime.
  2. memory grow will default to initialized with 0 as wasm spec.

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The exception is when the latest allocation is being freed. There's also the case when memory is imported (which means it's not necessarily zeroed), as well as the very niche case when the heap is reset (which also leaves the memory dirty upon future allocations).

You are correct in saying that memory.grow zeroes out the new memory, but the above cases still show why fields need to be zeroed when using the stub allocator.

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Okay, I understand your point.
Perhaps the safest approach here is to simply disable this optimization in stub rt.

// Explicit initializer
// Check if we need to initialize this field
const valueExpr: ExpressionRef = this.compileExpression(initializerNode, fieldType, Constraints.ConvImplicit);
// Memory will be filled with 0 on itcms.__new
// Memory grow will default to initialized with 0 as wasm spec
// So, optimize the active initialization away if it's zero
if (!this.canOptimizeZeroInitialization(valueExpr)) {
let expr = this.makeCallDirect(setterInstance, [
module.local_get(thisLocalIndex, sizeTypeRef),
valueExpr
], field.identifierNode, true);
if (this.currentType != Type.void) { // in case
expr = module.drop(expr);
}
stmts.push(expr);
}
}
stmts.push(expr);
}
}

Expand Down
59 changes: 7 additions & 52 deletions tests/compiler/assignment-chain.debug.wat
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Expand Up @@ -2250,35 +2250,30 @@
local.get $ptr
return
)
(func $assignment-chain/A#set:y (param $this i32) (param $y i64)
local.get $this
local.get $y
i64.store offset=8
)
(func $assignment-chain/A#set:x (param $this i32) (param $x i64)
local.get $this
local.get $x
i64.store
)
(func $assignment-chain/A#set:y (param $this i32) (param $y i64)
(func $assignment-chain/B#get:_setter_cnt (param $this i32) (result i32)
local.get $this
local.get $y
i64.store offset=8
i32.load
)
(func $assignment-chain/B#set:_setter_cnt (param $this i32) (param $_setter_cnt i32)
local.get $this
local.get $_setter_cnt
i32.store
)
(func $assignment-chain/B#set:_getter_cnt (param $this i32) (param $_getter_cnt i32)
local.get $this
local.get $_getter_cnt
i32.store offset=4
)
(func $assignment-chain/B#set:_y (param $this i32) (param $_y f64)
local.get $this
local.get $_y
f64.store offset=8
)
(func $assignment-chain/B#get:_setter_cnt (param $this i32) (result i32)
local.get $this
i32.load
)
(func $assignment-chain/B#get:_getter_cnt (param $this i32) (result i32)
local.get $this
i32.load offset=4
Expand Down Expand Up @@ -2434,22 +2429,6 @@
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i64.const 0
call $assignment-chain/A#set:x
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i64.const 0
call $assignment-chain/A#set:y
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
i32.const 8
i32.add
global.set $~lib/memory/__stack_pointer
Expand Down Expand Up @@ -2552,30 +2531,6 @@
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i32.const 0
call $assignment-chain/B#set:_setter_cnt
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i32.const 0
call $assignment-chain/B#set:_getter_cnt
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
f64.const 0
call $assignment-chain/B#set:_y
local.get $this
local.set $1
global.get $~lib/memory/__stack_pointer
i32.const 8
i32.add
global.set $~lib/memory/__stack_pointer
Expand Down
34 changes: 2 additions & 32 deletions tests/compiler/assignment-chain.release.wat
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Expand Up @@ -122,7 +122,7 @@
local.get $0
global.set $~lib/rt/itcms/iter
end
block $__inlined_func$~lib/rt/itcms/Object#unlink$129
block $__inlined_func$~lib/rt/itcms/Object#unlink$124
local.get $1
i32.load offset=4
i32.const -4
Expand All @@ -146,7 +146,7 @@
call $~lib/builtins/abort
unreachable
end
br $__inlined_func$~lib/rt/itcms/Object#unlink$129
br $__inlined_func$~lib/rt/itcms/Object#unlink$124
end
local.get $1
i32.load offset=8
Expand Down Expand Up @@ -1661,18 +1661,6 @@
local.tee $1
i32.store
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i64.const 0
i64.store
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i64.const 0
i64.store offset=8
global.get $~lib/memory/__stack_pointer
i32.const 8
i32.add
global.set $~lib/memory/__stack_pointer
Expand Down Expand Up @@ -1790,24 +1778,6 @@
local.tee $1
i32.store
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i32.const 0
i32.store
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
i32.const 0
i32.store offset=4
global.get $~lib/memory/__stack_pointer
local.get $1
i32.store offset=4
local.get $1
f64.const 0
f64.store offset=8
global.get $~lib/memory/__stack_pointer
i32.const 8
i32.add
global.set $~lib/memory/__stack_pointer
Expand Down
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