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[Stack Switching] Fix binary writing of continuation types when GC is not enabled #7827

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kripken wants to merge 3 commits into from
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[Stack Switching] Fix binary writing of continuation types when GC is not enabled #7827

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9d4cc20
fix
kripken Aug 14, 2025
997579e
fix
kripken Aug 14, 2025
1759b03
bettr
kripken Aug 14, 2025
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2 changes: 1 addition & 1 deletion src/wasm/wasm-binary.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -310,7 +310,7 @@ void WasmBinaryWriter::writeTypes() {
break;
case HeapTypeKind::Cont:
o << uint8_t(BinaryConsts::EncodedType::Cont);
writeHeapType(type.getContinuation().type, Inexact);
writeIndexedHeapType(type.getContinuation().type);
break;
case HeapTypeKind::Basic:
WASM_UNREACHABLE("unexpected kind");
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4 changes: 3 additions & 1 deletion src/wasm/wasm-stack.cpp
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Expand Up @@ -135,7 +135,9 @@ void BinaryInstWriter::visitCallIndirect(CallIndirect* curr) {
Index tableIdx = parent.getTableIndex(curr->table);
int8_t op =
curr->isReturn ? BinaryConsts::RetCallIndirect : BinaryConsts::CallIndirect;
o << op << U32LEB(parent.getTypeIndex(curr->heapType)) << U32LEB(tableIdx);
o << op;
parent.writeIndexedHeapType(curr->heapType);
o << U32LEB(tableIdx);
}

void BinaryInstWriter::visitLocalGet(LocalGet* curr) {
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29 changes: 29 additions & 0 deletions test/lit/basic/cont-no-gc.wast
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@@ -0,0 +1,29 @@
;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.

;; Test that we can write a binary without erroring when using stack switching
;; without GC. This verifies we can emit continuation types properly even when
;; GC is disabled

;; RUN: wasm-opt %s --enable-stack-switching --enable-reference-types --roundtrip -S -o - | filecheck %s

(module
;; CHECK: (type $proc (func))
(type $proc (func))
;; CHECK: (type $cont (cont $proc))
(type $cont (cont $proc))

;; CHECK: (func $main
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (cont.new $cont
;; CHECK-NEXT: (ref.func $main)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $main
(drop
(cont.new $cont
(ref.func $main)
)
Comment on lines +24 to +26
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@tlively tlively Aug 14, 2025

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Actually, this doesn't make any sense without typed function references. If the ref.func is just a funcref, then there's no way to validate that the continuation type has the the same parameters as the type of the function reference it is initialized with.

And we don't differentiate between typed-function-references and gc as features, so continuations without GC simply don't make sense.

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@kripken kripken Aug 14, 2025

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Wait, wasn't there an effort to avoid continuations from depending on GC?

Anyhow, I'm fine with making stack switching depend on GC, is that the right thing then?

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@tlively tlively Aug 14, 2025

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Yes, but they still depend on typed function references, and we don't differentiate between that and GC. So making stack switching depend on GC is the right thing for our purposes. We can revisit this in the future (probably by adding a separate typed-function-references feature again) if anyone really needs it.

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@kripken kripken Aug 15, 2025

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Ok, I opened #7830 and will close this.

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