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[TableGen][DecoderEmitter] Add helpers for working with scopes (NFC) #153979

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Aug 16, 2025
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[TableGen][DecoderEmitter] Add helpers for working with scopes (NFC) #153979

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47 changes: 18 additions & 29 deletions llvm/utils/TableGen/DecoderEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,17 @@ struct DecoderTableInfo {
DecoderSet Decoders;

bool isOutermostScope() const { return FixupStack.size() == 1; }

void pushScope() { FixupStack.emplace_back(); }

void popScope() {
// Resolve any remaining fixups in the current scope before popping it.
// All fixups resolve to the current location.
uint32_t DestIdx = Table.size();
for (uint32_t FixupIdx : FixupStack.back())
Table.patchNumToSkip(FixupIdx, DestIdx);
FixupStack.pop_back();
}
};

struct EncodingAndInst {
Expand Down Expand Up @@ -726,14 +737,6 @@ void Filter::recurse() {
}
}

static void resolveTableFixups(DecoderTable &Table, const FixupList &Fixups,
uint32_t DestIdx) {
// Any NumToSkip fixups in the current scope can resolve to the
// current location.
for (uint32_t FixupIdx : Fixups)
Table.patchNumToSkip(FixupIdx, DestIdx);
}

// Emit table entries to decode instructions given a segment or segments
// of bits.
void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
Expand All @@ -753,7 +756,7 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
const uint64_t LastFilter = FilterChooserMap.rbegin()->first;
bool HasFallthrough = LastFilter == NO_FIXED_SEGMENTS_SENTINEL;
if (HasFallthrough)
TableInfo.FixupStack.emplace_back();
TableInfo.pushScope();

DecoderTable &Table = TableInfo.Table;

Expand All @@ -765,13 +768,7 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
// Each scope should always have at least one filter value to check
// for.
assert(PrevFilter != 0 && "empty filter set!");
FixupList &CurScope = TableInfo.FixupStack.back();
// Resolve any NumToSkip fixups in the current scope.
resolveTableFixups(Table, CurScope, Table.size());

// Delete the scope we have added here.
TableInfo.FixupStack.pop_back();

TableInfo.popScope();
PrevFilter = 0; // Don't re-process the filter's fallthrough.
} else {
// The last filtervalue emitted can be OPC_FilterValue if we are at
Expand Down Expand Up @@ -1515,13 +1512,9 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,

// complex singletons need predicate checks from the first singleton
// to refer forward to the variable filterchooser that follows.
TableInfo.FixupStack.emplace_back();

TableInfo.pushScope();
emitSingletonTableEntry(TableInfo, Opc);

resolveTableFixups(TableInfo.Table, TableInfo.FixupStack.back(),
TableInfo.Table.size());
TableInfo.FixupStack.pop_back();
TableInfo.popScope();

Best.getVariableFC().emitTableEntries(TableInfo);
}
Expand Down Expand Up @@ -2623,16 +2616,12 @@ namespace {
// predicates and decoders themselves, however, are shared across all
// decoders to give more opportunities for uniqueing.
TableInfo.Table.clear();
TableInfo.FixupStack.clear();
TableInfo.FixupStack.emplace_back();
TableInfo.pushScope();
FC.emitTableEntries(TableInfo);
// Any NumToSkip fixups in the top level scope can resolve to the
// OPC_Fail at the end of the table.
assert(TableInfo.FixupStack.size() == 1 && "fixup stack phasing error!");
// Resolve any NumToSkip fixups in the current scope.
resolveTableFixups(TableInfo.Table, TableInfo.FixupStack.back(),
TableInfo.Table.size());
TableInfo.FixupStack.clear();
assert(TableInfo.isOutermostScope() && "fixup stack phasing error!");
TableInfo.popScope();

TableInfo.Table.push_back(MCD::OPC_Fail);

Expand Down