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[Custom Descriptors] Interpret descriptor casts #7677

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Jun 24, 2025
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[Custom Descriptors] Interpret descriptor casts #7677

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45 changes: 37 additions & 8 deletions src/wasm-interpreter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1651,6 +1651,36 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
return typename Cast::Failure{val};
}
}
template<typename T> Cast doDescCast(T* curr) {
Flow ref = self()->visit(curr->ref);
if (ref.breaking()) {
return typename Cast::Breaking{ref};
}
Flow desc = self()->visit(curr->desc);
if (desc.breaking()) {
return typename Cast::Breaking{ref};
}
auto expected = desc.getSingleValue().getGCData();
if (!expected) {
trap("null descriptor");
}
Literal val = ref.getSingleValue();
auto data = val.getGCData();
if (!data) {
// Check whether null is allowed.
if (curr->getCastType().isNullable()) {
return typename Cast::Success{val};
} else {
return typename Cast::Failure{val};
}
}
// The cast succeeds if we have the expected descriptor.
if (data->desc.getGCData() == expected) {
return typename Cast::Success{val};
} else {
return typename Cast::Failure{val};
}
}

Flow visitRefTest(RefTest* curr) {
NOTE_ENTER("RefTest");
Expand All @@ -1663,7 +1693,7 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
}
Flow visitRefCast(RefCast* curr) {
NOTE_ENTER("RefCast");
auto cast = doCast(curr);
auto cast = curr->desc ? doDescCast(curr) : doCast(curr);
if (auto* breaking = cast.getBreaking()) {
return *breaking;
} else if (auto* result = cast.getSuccess()) {
Expand All @@ -1690,29 +1720,28 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
// BrOnCast* uses the casting infrastructure, so handle them first.
switch (curr->op) {
case BrOnCast:
case BrOnCastFail: {
auto cast = doCast(curr);
case BrOnCastFail:
case BrOnCastDesc:
case BrOnCastDescFail: {
auto cast = curr->desc ? doDescCast(curr) : doCast(curr);
if (auto* breaking = cast.getBreaking()) {
return *breaking;
} else if (auto* original = cast.getFailure()) {
if (curr->op == BrOnCast) {
if (curr->op == BrOnCast || curr->op == BrOnCastDesc) {
return *original;
} else {
return Flow(curr->name, *original);
}
} else {
auto* result = cast.getSuccess();
assert(result);
if (curr->op == BrOnCast) {
if (curr->op == BrOnCast || curr->op == BrOnCastDesc) {
return Flow(curr->name, *result);
} else {
return *result;
}
}
}
case BrOnCastDesc:
case BrOnCastDescFail:
WASM_UNREACHABLE("TODO");
case BrOnNull:
case BrOnNonNull: {
// Otherwise we are just checking for null.
Expand Down
164 changes: 164 additions & 0 deletions test/spec/br_on_cast_desc.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,13 @@
(type $sub.desc (sub $super.desc (describes $sub (struct))))
)

(global $super.desc1 (ref (exact $super.desc)) (struct.new $super.desc))
(global $super.desc2 (ref (exact $super.desc)) (struct.new $super.desc))
(global $super1 (ref $super) (struct.new $super (global.get $super.desc1)))

(global $sub.desc (ref (exact $sub.desc)) (struct.new $sub.desc))
(global $sub (ref $sub) (struct.new $sub (global.get $sub.desc)))

;; br_on_cast_desc

(func $br_on_cast_desc-unreachable (result anyref)
Expand All @@ -33,6 +40,78 @@
)
(unreachable)
)
(func (export "cast-success") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref null $super)
(global.get $super1)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "cast-success-supertype") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref null $super)
(global.get $sub)
(global.get $sub.desc)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "cast-success-null") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref null $super)
(ref.null none)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "cast-fail-null") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref $super)
(ref.null none)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "cast-fail-wrong-desc") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref null $super)
(global.get $super1)
(global.get $super.desc2)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "cast-fail-null-desc") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc $l anyref (ref null $super)
(global.get $super1)
(ref.null none)
)
(return (i32.const 0))
)
)
(i32.const 1)
)

;; br_on_cast_desc_fail

Expand Down Expand Up @@ -61,8 +140,93 @@
)
)
)
(func (export "fail-cast-success") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref null $super)
(global.get $super1)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "fail-cast-success-supertype") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref null $super)
(global.get $sub)
(global.get $sub.desc)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "fail-cast-success-null") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref null $super)
(ref.null none)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "fail-cast-fail-null") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref $super)
(ref.null none)
(global.get $super.desc1)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "fail-cast-fail-wrong-desc") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref null $super)
(global.get $super1)
(global.get $super.desc2)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
(func (export "fail-cast-fail-null-desc") (result i32)
(drop
(block $l (result anyref)
(br_on_cast_desc_fail $l anyref (ref null $super)
(global.get $super1)
(ref.null none)
)
(return (i32.const 0))
)
)
(i32.const 1)
)
)

(assert_return (invoke "cast-success") (i32.const 1))
(assert_return (invoke "cast-success-supertype") (i32.const 1))
(assert_return (invoke "cast-success-null") (i32.const 1))
(assert_return (invoke "cast-fail-null") (i32.const 0))
(assert_return (invoke "cast-fail-wrong-desc") (i32.const 0))
(assert_trap (invoke "cast-fail-null-desc") "null descriptor")
(assert_return (invoke "fail-cast-success") (i32.const 0))
(assert_return (invoke "fail-cast-success-supertype") (i32.const 0))
(assert_return (invoke "fail-cast-success-null") (i32.const 0))
(assert_return (invoke "fail-cast-fail-null") (i32.const 1))
(assert_return (invoke "fail-cast-fail-wrong-desc") (i32.const 1))
(assert_trap (invoke "fail-cast-fail-null-desc") "null descriptor")

(assert_malformed
;; Input type must be a reference.
(module quote "(module (rec (type $struct (descriptor $desc (struct))) (type $desc (describes $struct (struct)))) (func (result anyref) (unreachable) (br_on_cast_desc 0 i32 (ref null $struct))))")
Expand Down
98 changes: 98 additions & 0 deletions test/spec/ref.cast_desc.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,13 @@
(type $sub.desc (sub $super.desc (describes $sub (struct))))
)

(global $super.desc1 (ref (exact $super.desc)) (struct.new $super.desc))
(global $super.desc2 (ref (exact $super.desc)) (struct.new $super.desc))
(global $super1 (ref $super) (struct.new $super (global.get $super.desc1)))

(global $sub.desc (ref (exact $sub.desc)) (struct.new $sub.desc))
(global $sub (ref $sub) (struct.new $sub (global.get $sub.desc)))

;; ref.cast_desc (ref null ht)

(func $ref.cast_desc-null-unreachable (result anyref)
Expand All @@ -32,6 +39,46 @@
(local.get $super.desc)
)
)
(func (export "cast-success")
(drop
(ref.cast_desc (ref null $super)
(global.get $super1)
(global.get $super.desc1)
)
)
)
(func (export "cast-success-supertype")
(drop
(ref.cast_desc (ref null $super)
(global.get $sub)
(global.get $sub.desc)
)
)
)
(func (export "cast-success-null")
(drop
(ref.cast_desc (ref null $super)
(ref.null none)
(global.get $super.desc1)
)
)
)
(func (export "cast-fail-wrong-desc")
(drop
(ref.cast_desc (ref null $super)
(global.get $super1)
(global.get $super.desc2)
)
)
)
(func (export "cast-fail-null-desc")
(drop
(ref.cast_desc (ref null $super)
(global.get $super1)
(ref.null none)
)
)
)

;; ref.cast_desc (ref ht)

Expand All @@ -58,8 +105,59 @@
(local.get $super.desc)
)
)
(func (export "cast-nn-success")
(drop
(ref.cast_desc (ref $super)
(global.get $super1)
(global.get $super.desc1)
)
)
)
(func (export "cast-nn-success-supertype")
(drop
(ref.cast_desc (ref $super)
(global.get $sub)
(global.get $sub.desc)
)
)
)
(func (export "cast-nn-fail-null")
(drop
(ref.cast_desc (ref $super)
(ref.null none)
(global.get $super.desc1)
)
)
)
(func (export "cast-nn-fail-wrong-desc")
(drop
(ref.cast_desc (ref $super)
(global.get $super1)
(global.get $super.desc2)
)
)
)
(func (export "cast-nn-fail-null-desc")
(drop
(ref.cast_desc (ref $super)
(global.get $super1)
(ref.null none)
)
)
)
)

(assert_return (invoke "cast-success"))
(assert_return (invoke "cast-success-supertype"))
(assert_return (invoke "cast-success-null"))
(assert_trap (invoke "cast-fail-wrong-desc") "cast error")
(assert_trap (invoke "cast-fail-null-desc") "null descriptor")
(assert_return (invoke "cast-nn-success"))
(assert_return (invoke "cast-nn-success-supertype"))
(assert_trap (invoke "cast-nn-fail-null") "cast error")
(assert_trap (invoke "cast-nn-fail-wrong-desc") "cast error")
(assert_trap (invoke "cast-nn-fail-null-desc") "null descriptor")

(assert_malformed
;; Cast type must be a reference.
(module quote "(module (func (unreachable) (ref.cast_desc i32) (unreachable)))")
Expand Down
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