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//===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// The MachineFrameInfo class represents an abstract stack frame until
// prolog/epilog code is inserted. This class is key to allowing stack frame
// representation optimizations, such as frame pointer elimination. It also
// allows more mundane (but still important) optimizations, such as reordering
// of abstract objects on the stack frame.
// To support this, the class assigns unique integer identifiers to stack
// objects requested clients. These identifiers are negative integers for fixed
// stack objects (such as arguments passed on the stack) or positive for objects
// that may be reordered. Instructions which refer to stack objects use a
// special MO_FrameIndex operand to represent these frame indexes.
// Because this class keeps track of all references to the stack frame, it knows
// when a variable sized object is allocated on the stack. This is the sole
// condition which prevents frame pointer elimination, which is an important
// optimization on register-poor architectures. Because original variable sized
// alloca's in the source program are the only source of variable sized stack
// objects, it is safe to decide whether there will be any variable sized
// objects before all stack objects are known (for example, register allocator
// spill code never needs variable sized objects).
// When prolog/epilog code emission is performed, the final stack frame is built
// and the machine instructions are modified to refer to the actual stack
// offsets of the object, eliminating all MO_FrameIndex operands from the
// program.
#include <vector>
namespace llvm {
class TargetData;
class TargetRegisterClass;
class Type;
class MachineFunction;
class MachineFrameInfo {
// StackObject - Represent a single object allocated on the stack.
struct StackObject {
// The size of this object on the stack. 0 means a variable sized object
unsigned Size;
// Alignment - The required alignment of this stack slot.
unsigned Alignment;
// SPOffset - The offset of this object from the stack pointer on entry to
// the function. This field has no meaning for a variable sized element.
int SPOffset;
StackObject(unsigned Sz, unsigned Al, int SP)
: Size(Sz), Alignment(Al), SPOffset(SP) {}
/// Objects - The list of stack objects allocated...
std::vector<StackObject> Objects;
/// NumFixedObjects - This contains the number of fixed objects contained on
/// the stack. Because fixed objects are stored at a negative index in the
/// Objects list, this is also the index to the 0th object in the list.
unsigned NumFixedObjects;
/// HasVarSizedObjects - This boolean keeps track of whether any variable
/// sized objects have been allocated yet.
bool HasVarSizedObjects;
/// StackSize - The prolog/epilog code inserter calculates the final stack
/// offsets for all of the fixed size objects, updating the Objects list
/// above. It then updates StackSize to contain the number of bytes that need
/// to be allocated on entry to the function.
unsigned StackSize;
/// HasCalls - Set to true if this function has any function calls. This is
/// only valid during and after prolog/epilog code insertion.
bool HasCalls;
/// MaxCallFrameSize - This contains the size of the largest call frame if the
/// target uses frame setup/destroy pseudo instructions (as defined in the
/// TargetFrameInfo class). This information is important for frame pointer
/// elimination. If is only valid during and after prolog/epilog code
/// insertion.
unsigned MaxCallFrameSize;
MachineFrameInfo() {
NumFixedObjects = StackSize = 0;
HasVarSizedObjects = false;
HasCalls = false;
MaxCallFrameSize = 0;
/// hasStackObjects - Return true if there are any stack objects in this
/// function.
bool hasStackObjects() const { return !Objects.empty(); }
/// hasVarSizedObjects - This method may be called any time after instruction
/// selection is complete to determine if the stack frame for this function
/// contains any variable sized objects.
bool hasVarSizedObjects() const { return HasVarSizedObjects; }
/// getObjectIndexBegin - Return the minimum frame object index...
int getObjectIndexBegin() const { return -NumFixedObjects; }
/// getObjectIndexEnd - Return one past the maximum frame object index...
int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
/// getObjectSize - Return the size of the specified object
int getObjectSize(int ObjectIdx) const {
assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
return Objects[ObjectIdx+NumFixedObjects].Size;
/// getObjectAlignment - Return the alignment of the specified stack object...
int getObjectAlignment(int ObjectIdx) const {
assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
return Objects[ObjectIdx+NumFixedObjects].Alignment;
/// getObjectOffset - Return the assigned stack offset of the specified object
/// from the incoming stack pointer.
int getObjectOffset(int ObjectIdx) const {
assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
return Objects[ObjectIdx+NumFixedObjects].SPOffset;
/// setObjectOffset - Set the stack frame offset of the specified object. The
/// offset is relative to the stack pointer on entry to the function.
void setObjectOffset(int ObjectIdx, int SPOffset) {
assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
/// getStackSize - Return the number of bytes that must be allocated to hold
/// all of the fixed size frame objects. This is only valid after
/// Prolog/Epilog code insertion has finalized the stack frame layout.
unsigned getStackSize() const { return StackSize; }
/// setStackSize - Set the size of the stack...
void setStackSize(unsigned Size) { StackSize = Size; }
/// hasCalls - Return true if the current function has no function calls.
/// This is only valid during or after prolog/epilog code emission.
bool hasCalls() const { return HasCalls; }
void setHasCalls(bool V) { HasCalls = V; }
/// getMaxCallFrameSize - Return the maximum size of a call frame that must be
/// allocated for an outgoing function call. This is only available if
/// CallFrameSetup/Destroy pseudo instructions are used by the target, and
/// then only during or after prolog/epilog code insertion.
unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
/// CreateFixedObject - Create a new object at a fixed location on the stack.
/// All fixed objects should be created before other objects are created for
/// efficiency. This returns an index with a negative value.
int CreateFixedObject(unsigned Size, int SPOffset) {
assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
return -++NumFixedObjects;
/// CreateStackObject - Create a new statically sized stack object, returning
/// a postive identifier to represent it.
int CreateStackObject(unsigned Size, unsigned Alignment) {
assert(Size != 0 && "Cannot allocate zero size stack objects!");
Objects.push_back(StackObject(Size, Alignment, -1));
return Objects.size()-NumFixedObjects-1;
/// CreateStackObject - Create a stack object for a value of the specified
/// LLVM type.
int CreateStackObject(const Type *Ty, const TargetData &TD);
/// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
/// variable sized object has been created. This must be created whenever a
/// variable sized object is created, whether or not the index returned is
/// actually used.
int CreateVariableSizedObject() {
HasVarSizedObjects = true;
Objects.push_back(StackObject(0, 1, -1));
return Objects.size()-NumFixedObjects-1;
/// print - Used by the MachineFunction printer to print information about
/// stack objects. Implemented in MachineFunction.cpp
void print(const MachineFunction &MF, std::ostream &OS) const;
/// dump - Call print(MF, std::cerr) to be called from the debugger.
void dump(const MachineFunction &MF) const;
} // End llvm namespace