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//===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Implements the layout of a stack frame on the target machine.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/BitVector.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
using namespace llvm;
TargetFrameLowering::~TargetFrameLowering() = default;
bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
!MF.getFunction().hasFnAttribute(Attribute::UWTable));
return false;
}
/// Returns the displacement from the frame register to the stack
/// frame of the specified index, along with the frame register used
/// (in output arg FrameReg). This is the default implementation which
/// is overridden for some targets.
int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
int FI, unsigned &FrameReg) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
// By default, assume all frame indices are referenced via whatever
// getFrameRegister() says. The target can override this if it's doing
// something different.
FrameReg = RI->getFrameRegister(MF);
return MFI.getObjectOffset(FI) + MFI.getStackSize() -
getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
}
bool TargetFrameLowering::needsFrameIndexResolution(
const MachineFunction &MF) const {
return MF.getFrameInfo().hasStackObjects();
}
void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
BitVector &SavedRegs,
RegScavenger *RS) const {
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
// Resize before the early returns. Some backends expect that
// SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
// saved registers.
SavedRegs.resize(TRI.getNumRegs());
// When interprocedural register allocation is enabled caller saved registers
// are preferred over callee saved registers.
if (MF.getTarget().Options.EnableIPRA &&
isSafeForNoCSROpt(MF.getFunction()) &&
isProfitableForNoCSROpt(MF.getFunction()))
return;
// Get the callee saved register list...
const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
// Early exit if there are no callee saved registers.
if (!CSRegs || CSRegs[0] == 0)
return;
// In Naked functions we aren't going to save any registers.
if (MF.getFunction().hasFnAttribute(Attribute::Naked))
return;
// Noreturn+nounwind functions never restore CSR, so no saves are needed.
// Purely noreturn functions may still return through throws, so those must
// save CSR for caller exception handlers.
//
// If the function uses longjmp to break out of its current path of
// execution we do not need the CSR spills either: setjmp stores all CSRs
// it was called with into the jmp_buf, which longjmp then restores.
if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
!MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
enableCalleeSaveSkip(MF))
return;
// Functions which call __builtin_unwind_init get all their registers saved.
bool CallsUnwindInit = MF.callsUnwindInit();
const MachineRegisterInfo &MRI = MF.getRegInfo();
for (unsigned i = 0; CSRegs[i]; ++i) {
unsigned Reg = CSRegs[i];
if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
SavedRegs.set(Reg);
}
}
unsigned TargetFrameLowering::getStackAlignmentSkew(
const MachineFunction &MF) const {
// When HHVM function is called, the stack is skewed as the return address
// is removed from the stack before we enter the function.
if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
return MF.getTarget().getAllocaPointerSize();
return 0;
}
bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
!F.hasFnAttribute(Attribute::NoRecurse))
return false;
// Function should not be optimized as tail call.
for (const User *U : F.users())
if (auto CS = ImmutableCallSite(U))
if (CS.isTailCall())
return false;
return true;
}
int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
llvm_unreachable("getInitialCFAOffset() not implemented!");
}
unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
const {
llvm_unreachable("getInitialCFARegister() not implemented!");
}
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