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Group locals by written type in binary writer #8568

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Merged
tlively merged 2 commits into from
Apr 2, 2026
Merged

Group locals by written type in binary writer #8568

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Group locals by written type in binary writer
tlively Apr 2, 2026
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1 change: 1 addition & 0 deletions src/wasm-stack.h
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Original file line number Diff line number Diff line change
Expand Up @@ -150,6 +150,7 @@ class BinaryInstWriter : public OverriddenVisitor<BinaryInstWriter> {
std::unordered_map<Type, size_t> numLocalsByType;

void noteLocalType(Type type, Index count = 1);
Index getNumLocalsForType(Type type);

// Keeps track of the binary index of the scratch locals used to lower
// tuple.extract. If there are multiple scratch locals of the same type, they
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21 changes: 18 additions & 3 deletions src/wasm/wasm-stack.cpp
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Expand Up @@ -3245,7 +3245,7 @@ void BinaryInstWriter::mapLocalsAndEmitHeader() {
Index baseIndex = func->getVarIndexBase();
for (auto& type : localTypes) {
nextFreeIndex[type] = baseIndex;
baseIndex += numLocalsByType[type];
baseIndex += getNumLocalsForType(type);
}

// Map the IR index pairs to indices.
Expand All @@ -3261,21 +3261,36 @@ void BinaryInstWriter::mapLocalsAndEmitHeader() {
scratchLocals[type] = nextFreeIndex[type];
}

o << U32LEB(numLocalsByType.size());
o << U32LEB(localTypes.size());
for (auto& localType : localTypes) {
o << U32LEB(numLocalsByType.at(localType));
o << U32LEB(getNumLocalsForType(localType));
parent.writeType(localType);
}
}

void BinaryInstWriter::noteLocalType(Type type, Index count) {
// Group types by the type they will eventually be written out as. For
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// example, we do not need to differentiate exact and inexact versions of the
// same reference type if custom descriptors is not enabled and the type will
// be written as inexact either way.
auto feats = parent.getModule()->features;
type = type.asWrittenGivenFeatures(feats);
auto& num = numLocalsByType[type];
if (num == 0) {
localTypes.push_back(type);
}
num += count;
}

Index BinaryInstWriter::getNumLocalsForType(Type type) {
auto feats = parent.getModule()->features;
type = type.asWrittenGivenFeatures(feats);
if (auto it = numLocalsByType.find(type); it != numLocalsByType.end()) {
return it->second;
}
return 0;
}

InsertOrderedMap<Type, Index> BinaryInstWriter::countScratchLocals() {
struct ScratchLocalFinder : PostWalker<ScratchLocalFinder> {
BinaryInstWriter& parent;
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