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Fix br_on_cast parsing with non-nullable extra values #9036

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Fix br_on_cast parsing with non-nullable extra values #9036

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b1d7b25
Fix br_on_cast parsing with non-nullable extra values
pttydou Aug 23, 2026
852506f
Limit nondefaultable local fixup to scratch locals
pttydou Aug 27, 2026
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7 changes: 6 additions & 1 deletion src/ir/type-updating.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -498,7 +498,9 @@ Type GlobalTypeRewriter::getTempTupleType(Tuple tuple) {

namespace TypeUpdating {

void handleNonDefaultableLocals(Function* func, Module& wasm) {
void handleNonDefaultableLocals(Function* func,
Module& wasm,
Index firstLocal) {
if (!wasm.features.hasReferenceTypes()) {
// No references, so no non-nullable ones at all.
return;
Expand All @@ -524,6 +526,9 @@ void handleNonDefaultableLocals(Function* func, Module& wasm) {
func, wasm, LocalStructuralDominance::NonNullableOnly);
std::unordered_set<Index> badIndexes;
for (auto index : info.nonDominatingIndices) {
if (index < firstLocal) {
continue;
}
badIndexes.insert(index);

// LocalStructuralDominance should have only looked at non-nullable indexes
Expand Down
5 changes: 4 additions & 1 deletion src/ir/type-updating.h
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Expand Up @@ -564,7 +564,10 @@ namespace TypeUpdating {
// them. Atm this turns them into nullable ones, and adds ref.as_non_null on
// their uses (which keeps the type of the users identical).
// This may also handle other types of nondefaultable locals in the future.
void handleNonDefaultableLocals(Function* func, Module& wasm);
// Ignore locals before firstLocal, if specified.
void handleNonDefaultableLocals(Function* func,
Module& wasm,
Index firstLocal = 0);

// Returns the type that a local should be, after handling of non-
// defaultability.
Expand Down
5 changes: 5 additions & 0 deletions src/parser/parse-5-defs.cpp
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Expand Up @@ -16,6 +16,8 @@

#include "wat-parser-internal.h"

#include "ir/type-updating.h"

namespace wasm::WATParser {

Result<> parseDefinitions(
Expand Down Expand Up @@ -46,6 +48,7 @@ Result<> parseDefinitions(
WithPosition with(ctx, decls.funcDefs[i].pos);
ctx.setSrcLoc(decls.funcDefs[i].annotations);
ctx.in.setAnnotations(std::move(decls.funcDefs[i].annotations));
auto firstScratchLocal = f->getNumLocals();
if (!f->imported()) {
CHECK_ERR(ctx.visitFunctionStart(f));
}
Expand All @@ -63,6 +66,8 @@ Result<> parseDefinitions(
if (auto* err = end.getErr()) {
return ctx.in.err(decls.funcDefs[i].pos, err->msg);
}
TypeUpdating::handleNonDefaultableLocals(
f, decls.wasm, firstScratchLocal);
Comment on lines +69 to +70

@tlively tlively Aug 27, 2026

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Let's not worry about the firstScratchLocal optimization and just call handleNonDefaultableLocals as-is. It's ok if it fixes locals that were used invalidly in the input; there are a few similar cases where we end up parsing and accepting invalid modules.

}
}

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2 changes: 1 addition & 1 deletion src/wasm/wasm-ir-builder.cpp
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Expand Up @@ -2302,7 +2302,7 @@ Result<> IRBuilder::makeBrOn(Index label,
case BrOnCast:
case BrOnCastDescEq:
if (out->isNullable()) {
resultType = Type(in->getHeapType(), NonNullable);
resultType = in->with(NonNullable);
} else {
resultType = *in;
}
Expand Down
100 changes: 100 additions & 0 deletions test/lit/basic/br-on-cast-extra-values.wast
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@@ -0,0 +1,100 @@
;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
;; RUN: wasm-opt %s -all --roundtrip -S -o - | filecheck %s

(module
;; CHECK: (type $s (struct))
(type $s (struct))
;; CHECK: (func $extra-values (type $1) (param $s (ref $s)) (result (ref $s) (ref $s))
;; CHECK-NEXT: (local $scratch (ref $s))
;; CHECK-NEXT: (local $scratch_3 (ref $s))
;; CHECK-NEXT: (local $scratch_4 (ref $s))
;; CHECK-NEXT: (local $scratch_5 (ref $s))
;; CHECK-NEXT: (local $scratch_2 (ref null $s))
;; CHECK-NEXT: (block $block1 (type $3) (result (ref $s) (ref $s))
;; CHECK-NEXT: (local.set $scratch_5
;; CHECK-NEXT: (block $block (result (ref $s))
;; CHECK-NEXT: (local.set $scratch_3
;; CHECK-NEXT: (local.get $s)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch
;; CHECK-NEXT: (local.get $s)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch_2
;; CHECK-NEXT: (local.get $scratch_3)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch_4
;; CHECK-NEXT: (br_on_cast $block (ref $s) (ref $s)
;; CHECK-NEXT: (local.get $scratch)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (br $block1
;; CHECK-NEXT: (tuple.make 2
;; CHECK-NEXT: (ref.as_non_null
;; CHECK-NEXT: (local.get $scratch_2)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $scratch_4)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (tuple.make 2
;; CHECK-NEXT: (ref.as_non_null
;; CHECK-NEXT: (local.get $scratch_2)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $scratch_5)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $extra-values (param $s (ref $s)) (result (ref $s) (ref $s))
local.get $s
local.get $s
br_on_cast 0 (ref $s) (ref $s)
)
;; CHECK: (func $exact (type $2) (param $s (ref (exact $s))) (result (ref (exact $s)) (ref null (exact $s)))
;; CHECK-NEXT: (local $scratch (ref (exact $s)))
;; CHECK-NEXT: (local $scratch_3 (ref (exact $s)))
;; CHECK-NEXT: (local $scratch_4 (ref (exact $s)))
;; CHECK-NEXT: (local $scratch_2 (ref null (exact $s)))
;; CHECK-NEXT: (local $scratch_5 (ref null (exact $s)))
;; CHECK-NEXT: (block $block1 (type $4) (result (ref (exact $s)) (ref null (exact $s)))
;; CHECK-NEXT: (local.set $scratch_5
;; CHECK-NEXT: (block $block (result (ref null (exact $s)))
;; CHECK-NEXT: (local.set $scratch_3
;; CHECK-NEXT: (local.get $s)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch
;; CHECK-NEXT: (local.get $s)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch_2
;; CHECK-NEXT: (local.get $scratch_3)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $scratch_4
;; CHECK-NEXT: (br_on_cast $block (ref (exact $s)) (ref (exact $s))
;; CHECK-NEXT: (local.get $scratch)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (br $block1
;; CHECK-NEXT: (tuple.make 2
;; CHECK-NEXT: (ref.as_non_null
;; CHECK-NEXT: (local.get $scratch_2)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $scratch_4)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (tuple.make 2
;; CHECK-NEXT: (ref.as_non_null
;; CHECK-NEXT: (local.get $scratch_2)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $scratch_5)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $exact (param $s (ref (exact $s)))
(result (ref (exact $s)) (ref null (exact $s)))
local.get $s
local.get $s
br_on_cast 0 (ref (exact $s)) (ref null (exact $s))
)
)