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[CFIInserter] Improve CSRSavedLocation struct. #168869

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[CFIInserter] Improve CSRSavedLocation struct. #168869

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720eb42
[CFIInserter] Improve `CSRSavedLocation` struct.
Nov 20, 2025
9d6fbb4
addressed review comments.
Nov 20, 2025
0db6b47
fixed a wrong assertion.
Nov 21, 2025
76b10c1
addressed review comments.
Dec 10, 2025
be1b8c1
addressed review comments.
mgudim Dec 16, 2025
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93 changes: 73 additions & 20 deletions llvm/lib/CodeGen/CFIInstrInserter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -88,19 +88,61 @@ class CFIInstrInserter : public MachineFunctionPass {
#define INVALID_REG UINT_MAX
#define INVALID_OFFSET INT_MAX
/// contains the location where CSR register is saved.
struct CSRSavedLocation {
CSRSavedLocation(std::optional<unsigned> R, std::optional<int> O)
: Reg(R), Offset(O) {
assert((Reg.has_value() ^ Offset.has_value()) &&
"Register and offset can not both be valid");
class CSRSavedLocation {
public:
enum Kind { Invalid, Register, CFAOffset };
Kind K = Invalid;

private:
union {
// Dwarf register number
unsigned Reg;
// CFA offset
int64_t Offset;
} U;

public:
CSRSavedLocation() { K = Kind::Invalid; }

static CSRSavedLocation createCFAOffset(int64_t Offset) {
CSRSavedLocation Loc;
Loc.K = Kind::CFAOffset;
Loc.U.Offset = Offset;
return Loc;
}
std::optional<unsigned> Reg;
std::optional<int> Offset;

bool operator==(const CSRSavedLocation &RHS) const {
return Reg == RHS.Reg && Offset == RHS.Offset;
static CSRSavedLocation createRegister(unsigned Reg) {
CSRSavedLocation Loc;
Loc.K = Kind::Register;
Loc.U.Reg = Reg;
return Loc;
}

bool isValid() const { return K != Kind::Invalid; }

unsigned getRegister() const {
assert(K == Kind::Register);
return U.Reg;
}

int64_t getOffset() const {
assert(K == Kind::CFAOffset);
return U.Offset;
}

bool operator==(const CSRSavedLocation &RHS) const {
if (K != RHS.K)
return false;
switch (K) {
case Kind::Invalid:
return !RHS.isValid();
case Kind::Register:
return getRegister() == RHS.getRegister();
case Kind::CFAOffset:
return getOffset() == RHS.getOffset();
}
llvm_unreachable("Unknown CSRSavedLocation Kind!");
}
bool operator!=(const CSRSavedLocation &RHS) const {
return !(*this == RHS);
}
Expand Down Expand Up @@ -277,13 +319,19 @@ void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) {
case MCCFIInstruction::OpValOffset:
break;
}
if (CSRReg || CSROffset) {
CSRSavedLocation Loc(CSRReg, CSROffset);
auto [It, Inserted] = CSRLocMap.insert({CFI.getRegister(), Loc});
if (!Inserted && It->second != Loc) {
assert((!CSRReg.has_value() || !CSROffset.has_value()) &&
"A register can only be at an offset from CFA or in another "
"register, but not both!");
CSRSavedLocation CSRLoc;
if (CSRReg)
CSRLoc = CSRSavedLocation::createRegister(*CSRReg);
else if (CSROffset)
CSRLoc = CSRSavedLocation::createCFAOffset(*CSROffset);
if (CSRLoc.isValid()) {
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@preames preames Dec 11, 2025

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I would prefer we not add the Invalid state. The prior code didn't need it, your switch based code shouldn't either. Is there a strong reason this needs to exist?

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@mgudim mgudim Dec 16, 2025

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It will be needed here: https://github.com/llvm/llvm-project/pull/168531/files#diff-54d9d06f60ce6c927ea0f2c1380a50bdf93c689d1781186966ef2234660e47c9R421

Unless we want to collect all callee-saved registers in a vector before we come to this line. But... we also need CFIs for exception handling (or something else) and I suspect it may require emitting CFIs for non-callee saved registers.

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@mgudim mgudim Dec 16, 2025

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EDIT: I don't think we'll ever need to care about CFIs for registers which are not returned by getCalleeSavedRegs, so we can make CFIInstrInserter only track those. That should save some memory too. I'll create a separate PR for that.

auto [It, Inserted] = CSRLocMap.insert({CFI.getRegister(), CSRLoc});
if (!Inserted && It->second != CSRLoc)
reportFatalInternalError(
"Different saved locations for the same CSR");
}
CSRSaved.set(CFI.getRegister());
}
}
Expand Down Expand Up @@ -403,14 +451,19 @@ bool CFIInstrInserter::insertCFIInstrs(MachineFunction &MF) {
assert(it != CSRLocMap.end() && "Reg should have an entry in CSRLocMap");
unsigned CFIIndex;
CSRSavedLocation RO = it->second;
if (!RO.Reg && RO.Offset) {
switch (RO.K) {
case CSRSavedLocation::CFAOffset: {
CFIIndex = MF.addFrameInst(
MCCFIInstruction::createOffset(nullptr, Reg, *RO.Offset));
} else {
assert((RO.Reg && !RO.Offset) &&
"Reg and Offset cannot both be valid/invalid");
MCCFIInstruction::createOffset(nullptr, Reg, RO.getOffset()));
break;
}
case CSRSavedLocation::Register: {
CFIIndex = MF.addFrameInst(
MCCFIInstruction::createRegister(nullptr, Reg, *RO.Reg));
MCCFIInstruction::createRegister(nullptr, Reg, RO.getRegister()));
break;
}
default:
llvm_unreachable("Invalid CSRSavedLocation!");
}
BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex);
Expand Down
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