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[threads] Simplify and generalize reftype writing without GC #6766

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Merged
tlively merged 2 commits into from
Jul 18, 2024
Merged

[threads] Simplify and generalize reftype writing without GC #6766

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[threads] Simplify and generalize reftype writing without GC
tlively Jul 17, 2024
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tlively Jul 18, 2024
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2 changes: 1 addition & 1 deletion scripts/fuzz_opt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -361,7 +361,7 @@ def is_git_repo():
'shared-absheaptype.wast',
'type-ssa-shared.wast',
'shared-ref_eq.wast',
'shared-null-no-gc.wast',
'shared-types-no-gc.wast',
]


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22 changes: 6 additions & 16 deletions src/wasm/wasm-binary.cpp
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Expand Up @@ -1520,23 +1520,13 @@ void WasmBinaryWriter::writeType(Type type) {
// internally use more refined versions of those types, but we cannot emit
// those more refined types.
if (!wasm->features.hasGC()) {
if (Type::isSubType(type, Type(HeapType::func, Nullable))) {
o << S32LEB(BinaryConsts::EncodedType::funcref);
return;
}
if (Type::isSubType(type, Type(HeapType::ext, Nullable))) {
o << S32LEB(BinaryConsts::EncodedType::externref);
return;
}
if (Type::isSubType(type, Type(HeapType::exn, Nullable))) {
o << S32LEB(BinaryConsts::EncodedType::exnref);
return;
}
if (Type::isSubType(type, Type(HeapType::string, Nullable))) {
o << S32LEB(BinaryConsts::EncodedType::stringref);
return;
auto ht = type.getHeapType();
if (ht.isBasic() && ht.getBasic(Unshared) == HeapType::string) {
// Do not overgeneralize stringref to anyref.
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@kripken kripken Jul 18, 2024

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Why not?

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@tlively tlively Jul 18, 2024

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We actually already have a couple tests for this case, and I wanted to avoid breaking them. It's admittedly a little odd (i.e. definitely wrong) that we're ok generalizing none to any even in cases where it is used for null strings, but we're not ok with generalizing stringref itself to anyref, but I don't think it's a big deal in practice since stringref effectively does not exist.

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@kripken kripken Jul 18, 2024

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Sounds good. Please add a comment though as the special-casing here looks surprising. lgtm with that.

type = Type(HeapTypes::string.getBasic(ht.getShared()), Nullable);
} else {
type = Type(type.getHeapType().getTop(), Nullable);
}
WASM_UNREACHABLE("bad type without GC");
}
auto heapType = type.getHeapType();
if (type.isNullable() && heapType.isBasic() && !heapType.isShared()) {
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15 changes: 11 additions & 4 deletions test/lit/basic/shared-null-no-gc.wast → test/lit/basic/shared-types-no-gc.wast
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@@ -1,19 +1,26 @@
;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.

;; Test that we can write a binary without crashing when using a shared bottom
;; type without GC enabled.
;; Test that we can write a binary without crashing when using shared reference
;; types without GC enabled.

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

(module
;; CHECK: (func $test
;; CHECK: (func $null
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (ref.null (shared nofunc))
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test
(func $null
(drop
(ref.null (shared func))
)
)

;; CHECK: (func $signature (result (ref null (shared func)))
;; CHECK-NEXT: (unreachable)
;; CHECK-NEXT: )
(func $signature (result (ref null (shared func)))
(unreachable)
)
)