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//===- llvm/CallingConvLower.h - Calling Conventions ------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file declares the CCState and CCValAssign classes, used for lowering
// and implementing calling conventions.
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/CodeGen/TargetCallingConv.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/Support/Alignment.h"
namespace llvm {
class CCState;
class MachineFunction;
class MVT;
class TargetRegisterInfo;
/// CCValAssign - Represent assignment of one arg/retval to a location.
class CCValAssign {
enum LocInfo {
Full, // The value fills the full location.
SExt, // The value is sign extended in the location.
ZExt, // The value is zero extended in the location.
AExt, // The value is extended with undefined upper bits.
SExtUpper, // The value is in the upper bits of the location and should be
// sign extended when retrieved.
ZExtUpper, // The value is in the upper bits of the location and should be
// zero extended when retrieved.
AExtUpper, // The value is in the upper bits of the location and should be
// extended with undefined upper bits when retrieved.
BCvt, // The value is bit-converted in the location.
Trunc, // The value is truncated in the location.
VExt, // The value is vector-widened in the location.
// FIXME: Not implemented yet. Code that uses AExt to mean
// vector-widen should be fixed to use VExt instead.
FPExt, // The floating-point value is fp-extended in the location.
Indirect // The location contains pointer to the value.
// TODO: a subset of the value is in the location.
// Holds one of:
// - the register that the value is assigned to;
// - the memory offset at which the value resides;
// - additional information about pending location; the exact interpretation
// of the data is target-dependent.
std::variant<Register, int64_t, unsigned> Data;
/// ValNo - This is the value number being assigned (e.g. an argument number).
unsigned ValNo;
/// isCustom - True if this arg/retval requires special handling.
unsigned isCustom : 1;
/// Information about how the value is assigned.
LocInfo HTP : 6;
/// ValVT - The type of the value being assigned.
/// LocVT - The type of the location being assigned to.
CCValAssign(LocInfo HTP, unsigned ValNo, MVT ValVT, MVT LocVT, bool IsCustom)
: ValNo(ValNo), isCustom(IsCustom), HTP(HTP), ValVT(ValVT), LocVT(LocVT) {
static CCValAssign getReg(unsigned ValNo, MVT ValVT, unsigned RegNo,
MVT LocVT, LocInfo HTP, bool IsCustom = false) {
CCValAssign Ret(HTP, ValNo, ValVT, LocVT, IsCustom);
Ret.Data = Register(RegNo);
return Ret;
static CCValAssign getCustomReg(unsigned ValNo, MVT ValVT, unsigned RegNo,
MVT LocVT, LocInfo HTP) {
return getReg(ValNo, ValVT, RegNo, LocVT, HTP, /*IsCustom=*/true);
static CCValAssign getMem(unsigned ValNo, MVT ValVT, int64_t Offset,
MVT LocVT, LocInfo HTP, bool IsCustom = false) {
CCValAssign Ret(HTP, ValNo, ValVT, LocVT, IsCustom);
Ret.Data = Offset;
return Ret;
static CCValAssign getCustomMem(unsigned ValNo, MVT ValVT, int64_t Offset,
MVT LocVT, LocInfo HTP) {
return getMem(ValNo, ValVT, Offset, LocVT, HTP, /*IsCustom=*/true);
static CCValAssign getPending(unsigned ValNo, MVT ValVT, MVT LocVT,
LocInfo HTP, unsigned ExtraInfo = 0) {
CCValAssign Ret(HTP, ValNo, ValVT, LocVT, false);
Ret.Data = ExtraInfo;
return Ret;
void convertToReg(unsigned RegNo) { Data = Register(RegNo); }
void convertToMem(int64_t Offset) { Data = Offset; }
unsigned getValNo() const { return ValNo; }
MVT getValVT() const { return ValVT; }
bool isRegLoc() const { return std::holds_alternative<Register>(Data); }
bool isMemLoc() const { return std::holds_alternative<int64_t>(Data); }
bool isPendingLoc() const { return std::holds_alternative<unsigned>(Data); }
bool needsCustom() const { return isCustom; }
Register getLocReg() const { return std::get<Register>(Data); }
int64_t getLocMemOffset() const { return std::get<int64_t>(Data); }
unsigned getExtraInfo() const { return std::get<unsigned>(Data); }
MVT getLocVT() const { return LocVT; }
LocInfo getLocInfo() const { return HTP; }
bool isExtInLoc() const {
return (HTP == AExt || HTP == SExt || HTP == ZExt);
bool isUpperBitsInLoc() const {
return HTP == AExtUpper || HTP == SExtUpper || HTP == ZExtUpper;
/// Describes a register that needs to be forwarded from the prologue to a
/// musttail call.
struct ForwardedRegister {
ForwardedRegister(Register VReg, MCPhysReg PReg, MVT VT)
: VReg(VReg), PReg(PReg), VT(VT) {}
Register VReg;
MCPhysReg PReg;
/// CCAssignFn - This function assigns a location for Val, updating State to
/// reflect the change. It returns 'true' if it failed to handle Val.
typedef bool CCAssignFn(unsigned ValNo, MVT ValVT,
MVT LocVT, CCValAssign::LocInfo LocInfo,
ISD::ArgFlagsTy ArgFlags, CCState &State);
/// CCCustomFn - This function assigns a location for Val, possibly updating
/// all args to reflect changes and indicates if it handled it. It must set
/// isCustom if it handles the arg and returns true.
typedef bool CCCustomFn(unsigned &ValNo, MVT &ValVT,
MVT &LocVT, CCValAssign::LocInfo &LocInfo,
ISD::ArgFlagsTy &ArgFlags, CCState &State);
/// CCState - This class holds information needed while lowering arguments and
/// return values. It captures which registers are already assigned and which
/// stack slots are used. It provides accessors to allocate these values.
class CCState {
CallingConv::ID CallingConv;
bool IsVarArg;
bool AnalyzingMustTailForwardedRegs = false;
MachineFunction &MF;
const TargetRegisterInfo &TRI;
SmallVectorImpl<CCValAssign> &Locs;
LLVMContext &Context;
// True if arguments should be allocated at negative offsets.
bool NegativeOffsets;
uint64_t StackSize;
Align MaxStackArgAlign;
SmallVector<uint32_t, 16> UsedRegs;
SmallVector<CCValAssign, 4> PendingLocs;
SmallVector<ISD::ArgFlagsTy, 4> PendingArgFlags;
// ByValInfo and SmallVector<ByValInfo, 4> ByValRegs:
// Vector of ByValInfo instances (ByValRegs) is introduced for byval registers
// tracking.
// Or, in another words it tracks byval parameters that are stored in
// general purpose registers.
// For 4 byte stack alignment,
// instance index means byval parameter number in formal
// arguments set. Assume, we have some "struct_type" with size = 4 bytes,
// then, for function "foo":
// i32 foo(i32 %p, %struct_type* %r, i32 %s, %struct_type* %t)
// ByValRegs[0] describes how "%r" is stored (Begin == r1, End == r2)
// ByValRegs[1] describes how "%t" is stored (Begin == r3, End == r4).
// In case of 8 bytes stack alignment,
// In function shown above, r3 would be wasted according to AAPCS rules.
// ByValRegs vector size still would be 2,
// while "%t" goes to the stack: it wouldn't be described in ByValRegs.
// Supposed use-case for this collection:
// 1. Initially ByValRegs is empty, InRegsParamsProcessed is 0.
// 2. HandleByVal fills up ByValRegs.
// 3. Argument analysis (LowerFormatArguments, for example). After
// some byval argument was analyzed, InRegsParamsProcessed is increased.
struct ByValInfo {
ByValInfo(unsigned B, unsigned E) : Begin(B), End(E) {}
// First register allocated for current parameter.
unsigned Begin;
// First after last register allocated for current parameter.
unsigned End;
SmallVector<ByValInfo, 4 > ByValRegs;
// InRegsParamsProcessed - shows how many instances of ByValRegs was proceed
// during argument analysis.
unsigned InRegsParamsProcessed;
CCState(CallingConv::ID CC, bool IsVarArg, MachineFunction &MF,
SmallVectorImpl<CCValAssign> &Locs, LLVMContext &Context,
bool NegativeOffsets = false);
void addLoc(const CCValAssign &V) {
LLVMContext &getContext() const { return Context; }
MachineFunction &getMachineFunction() const { return MF; }
CallingConv::ID getCallingConv() const { return CallingConv; }
bool isVarArg() const { return IsVarArg; }
/// Returns the size of the currently allocated portion of the stack.
uint64_t getStackSize() const { return StackSize; }
/// getAlignedCallFrameSize - Return the size of the call frame needed to
/// be able to store all arguments and such that the alignment requirement
/// of each of the arguments is satisfied.
uint64_t getAlignedCallFrameSize() const {
return alignTo(StackSize, MaxStackArgAlign);
/// isAllocated - Return true if the specified register (or an alias) is
/// allocated.
bool isAllocated(MCRegister Reg) const {
return UsedRegs[Reg / 32] & (1 << (Reg & 31));
/// AnalyzeFormalArguments - Analyze an array of argument values,
/// incorporating info about the formals into this state.
void AnalyzeFormalArguments(const SmallVectorImpl<ISD::InputArg> &Ins,
CCAssignFn Fn);
/// The function will invoke AnalyzeFormalArguments.
void AnalyzeArguments(const SmallVectorImpl<ISD::InputArg> &Ins,
CCAssignFn Fn) {
AnalyzeFormalArguments(Ins, Fn);
/// AnalyzeReturn - Analyze the returned values of a return,
/// incorporating info about the result values into this state.
void AnalyzeReturn(const SmallVectorImpl<ISD::OutputArg> &Outs,
CCAssignFn Fn);
/// CheckReturn - Analyze the return values of a function, returning
/// true if the return can be performed without sret-demotion, and
/// false otherwise.
bool CheckReturn(const SmallVectorImpl<ISD::OutputArg> &Outs,
CCAssignFn Fn);
/// AnalyzeCallOperands - Analyze the outgoing arguments to a call,
/// incorporating info about the passed values into this state.
void AnalyzeCallOperands(const SmallVectorImpl<ISD::OutputArg> &Outs,
CCAssignFn Fn);
/// AnalyzeCallOperands - Same as above except it takes vectors of types
/// and argument flags.
void AnalyzeCallOperands(SmallVectorImpl<MVT> &ArgVTs,
SmallVectorImpl<ISD::ArgFlagsTy> &Flags,
CCAssignFn Fn);
/// The function will invoke AnalyzeCallOperands.
void AnalyzeArguments(const SmallVectorImpl<ISD::OutputArg> &Outs,
CCAssignFn Fn) {
AnalyzeCallOperands(Outs, Fn);
/// AnalyzeCallResult - Analyze the return values of a call,
/// incorporating info about the passed values into this state.
void AnalyzeCallResult(const SmallVectorImpl<ISD::InputArg> &Ins,
CCAssignFn Fn);
/// A shadow allocated register is a register that was allocated
/// but wasn't added to the location list (Locs).
/// \returns true if the register was allocated as shadow or false otherwise.
bool IsShadowAllocatedReg(MCRegister Reg) const;
/// AnalyzeCallResult - Same as above except it's specialized for calls which
/// produce a single value.
void AnalyzeCallResult(MVT VT, CCAssignFn Fn);
/// getFirstUnallocated - Return the index of the first unallocated register
/// in the set, or Regs.size() if they are all allocated.
unsigned getFirstUnallocated(ArrayRef<MCPhysReg> Regs) const {
for (unsigned i = 0; i < Regs.size(); ++i)
if (!isAllocated(Regs[i]))
return i;
return Regs.size();
void DeallocateReg(MCPhysReg Reg) {
assert(isAllocated(Reg) && "Trying to deallocate an unallocated register");
/// AllocateReg - Attempt to allocate one register. If it is not available,
/// return zero. Otherwise, return the register, marking it and any aliases
/// as allocated.
MCRegister AllocateReg(MCPhysReg Reg) {
if (isAllocated(Reg))
return MCRegister();
return Reg;
/// Version of AllocateReg with extra register to be shadowed.
MCRegister AllocateReg(MCPhysReg Reg, MCPhysReg ShadowReg) {
if (isAllocated(Reg))
return MCRegister();
return Reg;
/// AllocateReg - Attempt to allocate one of the specified registers. If none
/// are available, return zero. Otherwise, return the first one available,
/// marking it and any aliases as allocated.
MCPhysReg AllocateReg(ArrayRef<MCPhysReg> Regs) {
unsigned FirstUnalloc = getFirstUnallocated(Regs);
if (FirstUnalloc == Regs.size())
return MCRegister(); // Didn't find the reg.
// Mark the register and any aliases as allocated.
MCPhysReg Reg = Regs[FirstUnalloc];
return Reg;
/// AllocateRegBlock - Attempt to allocate a block of RegsRequired consecutive
/// registers. If this is not possible, return zero. Otherwise, return the first
/// register of the block that were allocated, marking the entire block as allocated.
MCPhysReg AllocateRegBlock(ArrayRef<MCPhysReg> Regs, unsigned RegsRequired) {
if (RegsRequired > Regs.size())
return 0;
for (unsigned StartIdx = 0; StartIdx <= Regs.size() - RegsRequired;
++StartIdx) {
bool BlockAvailable = true;
// Check for already-allocated regs in this block
for (unsigned BlockIdx = 0; BlockIdx < RegsRequired; ++BlockIdx) {
if (isAllocated(Regs[StartIdx + BlockIdx])) {
BlockAvailable = false;
if (BlockAvailable) {
// Mark the entire block as allocated
for (unsigned BlockIdx = 0; BlockIdx < RegsRequired; ++BlockIdx) {
MarkAllocated(Regs[StartIdx + BlockIdx]);
return Regs[StartIdx];
// No block was available
return 0;
/// Version of AllocateReg with list of registers to be shadowed.
MCRegister AllocateReg(ArrayRef<MCPhysReg> Regs, const MCPhysReg *ShadowRegs) {
unsigned FirstUnalloc = getFirstUnallocated(Regs);
if (FirstUnalloc == Regs.size())
return MCRegister(); // Didn't find the reg.
// Mark the register and any aliases as allocated.
MCRegister Reg = Regs[FirstUnalloc], ShadowReg = ShadowRegs[FirstUnalloc];
return Reg;
/// AllocateStack - Allocate a chunk of stack space with the specified size
/// and alignment.
int64_t AllocateStack(unsigned Size, Align Alignment) {
int64_t Offset;
if (NegativeOffsets) {
StackSize = alignTo(StackSize + Size, Alignment);
Offset = -StackSize;
} else {
Offset = alignTo(StackSize, Alignment);
StackSize = Offset + Size;
MaxStackArgAlign = std::max(Alignment, MaxStackArgAlign);
return Offset;
void ensureMaxAlignment(Align Alignment);
/// Version of AllocateStack with list of extra registers to be shadowed.
/// Note that, unlike AllocateReg, this shadows ALL of the shadow registers.
int64_t AllocateStack(unsigned Size, Align Alignment,
ArrayRef<MCPhysReg> ShadowRegs) {
for (MCPhysReg Reg : ShadowRegs)
return AllocateStack(Size, Alignment);
// HandleByVal - Allocate a stack slot large enough to pass an argument by
// value. The size and alignment information of the argument is encoded in its
// parameter attribute.
void HandleByVal(unsigned ValNo, MVT ValVT, MVT LocVT,
CCValAssign::LocInfo LocInfo, int MinSize, Align MinAlign,
ISD::ArgFlagsTy ArgFlags);
// Returns count of byval arguments that are to be stored (even partly)
// in registers.
unsigned getInRegsParamsCount() const { return ByValRegs.size(); }
// Returns count of byval in-regs arguments processed.
unsigned getInRegsParamsProcessed() const { return InRegsParamsProcessed; }
// Get information about N-th byval parameter that is stored in registers.
// Here "ByValParamIndex" is N.
void getInRegsParamInfo(unsigned InRegsParamRecordIndex,
unsigned& BeginReg, unsigned& EndReg) const {
assert(InRegsParamRecordIndex < ByValRegs.size() &&
"Wrong ByVal parameter index");
const ByValInfo& info = ByValRegs[InRegsParamRecordIndex];
BeginReg = info.Begin;
EndReg = info.End;
// Add information about parameter that is kept in registers.
void addInRegsParamInfo(unsigned RegBegin, unsigned RegEnd) {
ByValRegs.push_back(ByValInfo(RegBegin, RegEnd));
// Goes either to next byval parameter (excluding "waste" record), or
// to the end of collection.
// Returns false, if end is reached.
bool nextInRegsParam() {
unsigned e = ByValRegs.size();
if (InRegsParamsProcessed < e)
return InRegsParamsProcessed < e;
// Clear byval registers tracking info.
void clearByValRegsInfo() {
InRegsParamsProcessed = 0;
// Rewind byval registers tracking info.
void rewindByValRegsInfo() {
InRegsParamsProcessed = 0;
// Get list of pending assignments
SmallVectorImpl<CCValAssign> &getPendingLocs() {
return PendingLocs;
// Get a list of argflags for pending assignments.
SmallVectorImpl<ISD::ArgFlagsTy> &getPendingArgFlags() {
return PendingArgFlags;
/// Compute the remaining unused register parameters that would be used for
/// the given value type. This is useful when varargs are passed in the
/// registers that normal prototyped parameters would be passed in, or for
/// implementing perfect forwarding.
void getRemainingRegParmsForType(SmallVectorImpl<MCPhysReg> &Regs, MVT VT,
CCAssignFn Fn);
/// Compute the set of registers that need to be preserved and forwarded to
/// any musttail calls.
void analyzeMustTailForwardedRegisters(
SmallVectorImpl<ForwardedRegister> &Forwards, ArrayRef<MVT> RegParmTypes,
CCAssignFn Fn);
/// Returns true if the results of the two calling conventions are compatible.
/// This is usually part of the check for tailcall eligibility.
static bool resultsCompatible(CallingConv::ID CalleeCC,
CallingConv::ID CallerCC, MachineFunction &MF,
LLVMContext &C,
const SmallVectorImpl<ISD::InputArg> &Ins,
CCAssignFn CalleeFn, CCAssignFn CallerFn);
/// The function runs an additional analysis pass over function arguments.
/// It will mark each argument with the attribute flag SecArgPass.
/// After running, it will sort the locs list.
template <class T>
void AnalyzeArgumentsSecondPass(const SmallVectorImpl<T> &Args,
CCAssignFn Fn) {
unsigned NumFirstPassLocs = Locs.size();
/// Creates similar argument list to \p Args in which each argument is
/// marked using SecArgPass flag.
SmallVector<T, 16> SecPassArg;
// SmallVector<ISD::InputArg, 16> SecPassArg;
for (auto Arg : Args) {
// Run the second argument pass
AnalyzeArguments(SecPassArg, Fn);
// Sort the locations of the arguments according to their original position.
SmallVector<CCValAssign, 16> TmpArgLocs;
auto B = TmpArgLocs.begin(), E = TmpArgLocs.end();
std::merge(B, B + NumFirstPassLocs, B + NumFirstPassLocs, E,
[](const CCValAssign &A, const CCValAssign &B) -> bool {
return A.getValNo() < B.getValNo();
/// MarkAllocated - Mark a register and all of its aliases as allocated.
void MarkAllocated(MCPhysReg Reg);
void MarkUnallocated(MCPhysReg Reg);
} // end namespace llvm