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[GTO] Avoid newly exposing prototypes when supertype fields are removed #9278

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Merged
tlively merged 1 commit into from
Oct 19, 2026
Merged

[GTO] Avoid newly exposing prototypes when supertype fields are removed #9278

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8 changes: 5 additions & 3 deletions src/passes/GlobalTypeOptimization.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -372,6 +372,7 @@ struct GlobalTypeOptimization : public Pass {
// That is, we can only append fields: we cannot reorder or remove any
// field that is in the super.
Index numSuperFields = 0;
bool superHasKeptFields = false;
if (super) {
// We have visited the super before. Get the information about its
// fields.
Expand Down Expand Up @@ -408,6 +409,7 @@ struct GlobalTypeOptimization : public Pass {
// The super kept this field, so we must keep it as well. This can
// happen when we need the field in both, but also in the corner
// case where we don't need the field but the super is public.
superHasKeptFields = true;

// We need to keep it at the same index so we remain compatible.
indexesAfterRemoval[i] = superIndex;
Expand All @@ -433,10 +435,10 @@ struct GlobalTypeOptimization : public Pass {
}
}

// If the type has no supertype (or its supertype has no fields), check
// if its first field becomes prototype-exposing. If so, add a
// If the type has no supertype (or its supertype has no kept fields),
// check if its first field becomes prototype-exposing. If so, add a
// placeholder at index 0 and shift all computed indices.
if (isExposedNoProto && (!super || super->getStruct().fields.empty())) {
if (isExposedNoProto && !superHasKeptFields) {
// Find the field that will become field 0.
Index i = 0;
for (; i < fields.size(); ++i) {
Expand Down
61 changes: 61 additions & 0 deletions test/lit/passes/gto-jsinterop.wast
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Expand Up @@ -1753,3 +1753,64 @@
)
)
)

(module
;; All fields of $super-desc are unread and removed by GTO, leaving
;; $super-desc empty after optimization. In $sub-desc, the unread supertype
;; field is also removed and the following externref field shifts to index 0,
;; so $sub-desc must get an i8 placeholder at index 0 to avoid exposing a
;; prototype.
(rec
;; CHECK: (rec
;; CHECK-NEXT: (type $super (sub (descriptor $super-desc) (struct)))
(type $super (sub (descriptor $super-desc) (struct)))
;; CHECK: (type $super-desc (sub (describes $super) (struct)))
(type $super-desc (sub (describes $super) (struct (field f64))))
;; CHECK: (type $sub (sub final $super (descriptor $sub-desc) (struct)))
(type $sub (sub final $super (descriptor $sub-desc) (struct)))
;; CHECK: (type $sub-desc (sub final $super-desc (describes $sub) (struct (field i8) (field externref))))
(type $sub-desc (sub final $super-desc (describes $sub) (struct (field f64) (field externref))))
)

;; CHECK: (type $4 (func (param (ref $sub-desc)) (result externref)))

;; CHECK: (type $5 (func (result externref)))

;; CHECK: (import "env" "ext" (global $ext externref))
(import "env" "ext" (global $ext externref))
;; CHECK: (export "export" (func $test))
(export "export" (func $test))

;; CHECK: (func $test (type $5) (result externref)
;; CHECK-NEXT: (extern.convert_any
;; CHECK-NEXT: (struct.new_default_desc $sub
;; CHECK-NEXT: (struct.new $sub-desc
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: (global.get $ext)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test (result externref)
;; Convert to extern to expose the value to JS.
(extern.convert_any
(struct.new_default_desc $sub
(struct.new $sub-desc
(f64.const 0)
(global.get $ext)
)
)
)
)

;; CHECK: (func $use (type $4) (param $d (ref $sub-desc)) (result externref)
;; CHECK-NEXT: (struct.get $sub-desc 1
;; CHECK-NEXT: (local.get $d)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $use (param $d (ref $sub-desc)) (result externref)
(struct.get $sub-desc 1
(local.get $d)
)
)
)
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