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[NFC][AsmPrinter] Refactor FrameIndexExprs as a std::set #66433

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Sep 20, 2023
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[NFC][AsmPrinter] Refactor FrameIndexExprs as a std::set #66433

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47 changes: 17 additions & 30 deletions llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -265,6 +265,20 @@ static DbgValueLoc getDebugLocValue(const MachineInstr *MI) {
return DbgValueLoc(Expr, DbgValueLocEntries, IsVariadic);
}

static uint64_t getFragmentOffsetInBits(const DIExpression &Expr) {
std::optional<DIExpression::FragmentInfo> Fragment = Expr.getFragmentInfo();
return Fragment ? Fragment->OffsetInBits : 0;
}

bool llvm::operator<(const FrameIndexExpr &LHS, const FrameIndexExpr &RHS) {
return getFragmentOffsetInBits(*LHS.Expr) <
getFragmentOffsetInBits(*RHS.Expr);
}

bool llvm::operator<(const EntryValueInfo &LHS, const EntryValueInfo &RHS) {
return getFragmentOffsetInBits(LHS.Expr) < getFragmentOffsetInBits(RHS.Expr);
}

Loc::Single::Single(DbgValueLoc ValueLoc)
: ValueLoc(std::make_unique<DbgValueLoc>(ValueLoc)),
Expr(ValueLoc.getExpression()) {
Expand All @@ -275,42 +289,15 @@ Loc::Single::Single(DbgValueLoc ValueLoc)
Loc::Single::Single(const MachineInstr *DbgValue)
: Single(getDebugLocValue(DbgValue)) {}

ArrayRef<FrameIndexExpr> Loc::MMI::getFrameIndexExprs() const {
if (FrameIndexExprs.size() == 1)
return FrameIndexExprs;

assert(llvm::all_of(
FrameIndexExprs,
[](const FrameIndexExpr &A) { return A.Expr->isFragment(); }) &&
"multiple FI expressions without DW_OP_LLVM_fragment");
llvm::sort(FrameIndexExprs,
[](const FrameIndexExpr &A, const FrameIndexExpr &B) -> bool {
return A.Expr->getFragmentInfo()->OffsetInBits <
B.Expr->getFragmentInfo()->OffsetInBits;
});

const std::set<FrameIndexExpr> &Loc::MMI::getFrameIndexExprs() const {
return FrameIndexExprs;
}

void Loc::MMI::addFrameIndexExpr(const DIExpression *Expr, int FI) {
// FIXME: This logic should not be necessary anymore, as we now have proper
// deduplication. However, without it, we currently run into the assertion
// below, which means that we are likely dealing with broken input, i.e. two
// non-fragment entries for the same variable at different frame indices.
if (FrameIndexExprs.size()) {
auto *Expr = FrameIndexExprs.back().Expr;
if (!Expr || !Expr->isFragment())
return;
}

if (llvm::none_of(FrameIndexExprs, [&](const FrameIndexExpr &Other) {
return FI == Other.FI && Expr == Other.Expr;
}))
FrameIndexExprs.push_back({FI, Expr});

FrameIndexExprs.insert({FI, Expr});
assert((FrameIndexExprs.size() == 1 ||
llvm::all_of(FrameIndexExprs,
[](FrameIndexExpr &FIE) {
[](const FrameIndexExpr &FIE) {
return FIE.Expr && FIE.Expr->isFragment();
})) &&
"conflicting locations for variable");
Expand Down
17 changes: 6 additions & 11 deletions llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,9 @@ class DbgVariable;
struct FrameIndexExpr {
int FI;
const DIExpression *Expr;

/// Operator enabling sorting based on fragment offset.
friend bool operator<(const FrameIndexExpr &LHS, const FrameIndexExpr &RHS);
};

/// Represents an entry-value location, or a fragment of one.
Expand All @@ -115,15 +118,7 @@ struct EntryValueInfo {
const DIExpression &Expr;

/// Operator enabling sorting based on fragment offset.
bool operator<(const EntryValueInfo &Other) const {
return getFragmentOffsetInBits() < Other.getFragmentOffsetInBits();
}

private:
uint64_t getFragmentOffsetInBits() const {
std::optional<DIExpression::FragmentInfo> Fragment = Expr.getFragmentInfo();
return Fragment ? Fragment->OffsetInBits : 0;
}
friend bool operator<(const EntryValueInfo &LHS, const EntryValueInfo &RHS);
};

// Namespace for alternatives of a DbgVariable.
Expand Down Expand Up @@ -158,7 +153,7 @@ class Multi {
};
/// Single location defined by (potentially multiple) MMI entries.
struct MMI {
mutable SmallVector<FrameIndexExpr, 1> FrameIndexExprs;
std::set<FrameIndexExpr> FrameIndexExprs;
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Another possibilty would be a SetVector? (though then it's insertion ordered, rather than < ordered - not sure if that's sufficiently stable for the needs? perhaps not)

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I think we don't need the extra functionality provided by the SetVector here: our sorting keys (fragment offsets) are stable without the need for insertion-order-tracking.

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IIUC the DWARF emitter also wants the fragments ordered by offset? I'm not sure what would happen if we were to emit DWARF fragment expressions out of order 🤔

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IIUC the DWARF emitter also wants the fragments ordered by offset? I'm not sure what would happen if we were to emit DWARF fragment expressions out of order 🤔

Ah, yeah - DWARF does require the fragments be in order (essentially they don't say where they are in the structure - so you have to emit the first byte first, second byte second, etc)


public:
explicit MMI(const DIExpression *E, int FI) : FrameIndexExprs({{FI, E}}) {
Expand All @@ -167,7 +162,7 @@ struct MMI {
}
void addFrameIndexExpr(const DIExpression *Expr, int FI);
/// Get the FI entries, sorted by fragment offset.
ArrayRef<FrameIndexExpr> getFrameIndexExprs() const;
const std::set<FrameIndexExpr> &getFrameIndexExprs() const;
};
/// Single location defined by (potentially multiple) EntryValueInfo.
struct EntryValue {
Expand Down