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[TableGen][DecoderEmitter] Extract a couple of methods (NFC) #155044

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Aug 22, 2025
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[TableGen][DecoderEmitter] Extract a couple of methods (NFC) #155044

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106 changes: 55 additions & 51 deletions llvm/utils/TableGen/DecoderEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -612,19 +612,19 @@ class FilterChooser {
void emitDecoder(raw_ostream &OS, indent Indent, unsigned EncodingID) const;
unsigned getDecoderIndex(DecoderSet &Decoders, unsigned EncodingID) const;

// Assign a single filter and run with it.
void runSingleFilter(unsigned startBit, unsigned numBit);

// reportRegion is a helper function for filterProcessor to mark a region as
// eligible for use as a filter region.
void reportRegion(std::vector<std::unique_ptr<Filter>> &Filters, bitAttr_t RA,
unsigned StartBit, unsigned BitIndex, bool AllowMixed);
unsigned StartBit, unsigned BitIndex,
bool AllowMixed) const;

/// Scans the well-known encoding bits of the encodings and, builds up a list
/// of candidate filters, and then returns the best one, if any.
std::unique_ptr<Filter> findBestFilter(ArrayRef<bitAttr_t> BitAttrs,
bool AllowMixed,
bool Greedy = true) const;

// FilterProcessor scans the well-known encoding bits of the instructions and
// builds up a list of candidate filters. It chooses the best filter and
// recursively descends down the decoding tree.
bool filterProcessor(ArrayRef<bitAttr_t> BitAttrs, bool AllowMixed,
bool Greedy = true);
std::unique_ptr<Filter> findBestFilter() const;

// Decides on the best configuration of filter(s) to use in order to decode
// the instructions. A conflict of instructions may occur, in which case we
Expand All @@ -635,6 +635,8 @@ class FilterChooser {
// emitTableEntries - Emit state machine entries to decode our share of
// instructions.
void emitTableEntries(DecoderTableInfo &TableInfo) const;

void dump() const;
};

} // end anonymous namespace
Expand Down Expand Up @@ -1456,28 +1458,19 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
Best.getVariableFC().emitTableEntries(TableInfo);
}

// Assign a single filter and run with it. Top level API client can initialize
// with a single filter to start the filtering process.
void FilterChooser::runSingleFilter(unsigned startBit, unsigned numBit) {
BestFilter = std::make_unique<Filter>(*this, startBit, numBit);
BestFilter->recurse();
}

// reportRegion is a helper function for filterProcessor to mark a region as
// eligible for use as a filter region.
void FilterChooser::reportRegion(std::vector<std::unique_ptr<Filter>> &Filters,
bitAttr_t RA, unsigned StartBit,
unsigned BitIndex, bool AllowMixed) {
unsigned BitIndex, bool AllowMixed) const {
if (AllowMixed ? RA == ATTR_MIXED : RA == ATTR_ALL_SET)
Filters.push_back(
std::make_unique<Filter>(*this, StartBit, BitIndex - StartBit));
}

// FilterProcessor scans the well-known encoding bits of the instructions and
// builds up a list of candidate filters. It chooses the best filter and
// recursively descends down the decoding tree.
bool FilterChooser::filterProcessor(ArrayRef<bitAttr_t> BitAttrs,
bool AllowMixed, bool Greedy) {
std::unique_ptr<Filter>
FilterChooser::findBestFilter(ArrayRef<bitAttr_t> BitAttrs, bool AllowMixed,
bool Greedy) const {
assert(EncodingIDs.size() >= 2 && "Nothing to filter");

// Heuristics. See also doFilter()'s "Heuristics" comment when num of
Expand All @@ -1493,8 +1486,8 @@ bool FilterChooser::filterProcessor(ArrayRef<bitAttr_t> BitAttrs,
std::vector<Island> Islands = getIslands(EncodingBits);
if (!Islands.empty()) {
// Found an instruction with island(s). Now just assign a filter.
runSingleFilter(Islands[0].StartBit, Islands[0].NumBits);
return true;
return std::make_unique<Filter>(*this, Islands[0].StartBit,
Islands[0].NumBits);
}
}
}
Expand Down Expand Up @@ -1633,24 +1626,12 @@ bool FilterChooser::filterProcessor(ArrayRef<bitAttr_t> BitAttrs,
}

if (AllUseless)
return false;

BestFilter = std::move(Filters[BestIndex]);
BestFilter->recurse();
return true;

} // end of FilterChooser::filterProcessor(bool)

// Decides on the best configuration of filter(s) to use in order to decode
// the instructions. A conflict of instructions may occur, in which case we
// dump the conflict set to the standard error.
void FilterChooser::doFilter() {
assert(!EncodingIDs.empty() && "FilterChooser created with no instructions");
return nullptr;

// No filter needed.
if (EncodingIDs.size() < 2)
return;
return std::move(Filters[BestIndex]);
}

std::unique_ptr<Filter> FilterChooser::findBestFilter() const {
// We maintain BIT_WIDTH copies of the bitAttrs automaton.
// The automaton consumes the corresponding bit from each
// instruction.
Expand Down Expand Up @@ -1706,32 +1687,56 @@ void FilterChooser::doFilter() {
}

// Try regions of consecutive known bit values first.
if (filterProcessor(BitAttrs, /*AllowMixed=*/false))
return;
if (std::unique_ptr<Filter> F =
findBestFilter(BitAttrs, /*AllowMixed=*/false))
return F;

// Then regions of mixed bits (both known and unitialized bit values allowed).
if (filterProcessor(BitAttrs, /*AllowMixed=*/true))
return;
if (std::unique_ptr<Filter> F = findBestFilter(BitAttrs, /*AllowMixed=*/true))
return F;

// Heuristics to cope with conflict set {t2CMPrs, t2SUBSrr, t2SUBSrs} where
// no single instruction for the maximum ATTR_MIXED region Inst{14-4} has a
// well-known encoding pattern. In such case, we backtrack and scan for the
// the very first consecutive ATTR_ALL_SET region and assign a filter to it.
if (EncodingIDs.size() == 3 &&
filterProcessor(BitAttrs, /*AllowMixed=*/true, /*Greedy=*/false))
if (EncodingIDs.size() == 3) {
if (std::unique_ptr<Filter> F =
findBestFilter(BitAttrs, /*AllowMixed=*/true, /*Greedy=*/false))
return F;
}

// There is a conflict we could not resolve.
return nullptr;
}

// Decides on the best configuration of filter(s) to use in order to decode
// the instructions. A conflict of instructions may occur, in which case we
// dump the conflict set to the standard error.
void FilterChooser::doFilter() {
assert(!EncodingIDs.empty() && "FilterChooser created with no instructions");

// No filter needed.
if (EncodingIDs.size() < 2)
return;

// We don't know how to decode these instructions! Dump the
// conflict set and bail.
assert(!BestFilter);
BestFilter = findBestFilter();
if (BestFilter) {
BestFilter->recurse();
return;
}

// Print out useful conflict information for postmortem analysis.
errs() << "Decoding Conflict:\n";
dump();
PrintFatalError("Decoding conflict encountered");
}

// Dump filters.
void FilterChooser::dump() const {
indent Indent(4);
// Helps to keep the output right-justified.
unsigned PadToWidth = getMaxEncodingWidth();

// Dump filter stack.
dumpStack(errs(), Indent, PadToWidth);

// Dump encodings.
Expand All @@ -1741,7 +1746,6 @@ void FilterChooser::doFilter() {
printKnownBits(errs(), Encoding.getMandatoryBits(), '_');
errs() << " " << Encoding.getName() << '\n';
}
PrintFatalError("Decoding conflict encountered");
}

// emitTableEntries - Emit state machine entries to decode our share of
Expand Down