1 //===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // Implements the layout of a stack frame on the target machine.
11 //===----------------------------------------------------------------------===//
13 #include "llvm/CodeGen/TargetFrameLowering.h"
14 #include "llvm/ADT/BitVector.h"
15 #include "llvm/CodeGen/MachineFrameInfo.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineRegisterInfo.h"
18 #include "llvm/CodeGen/TargetRegisterInfo.h"
19 #include "llvm/CodeGen/TargetSubtargetInfo.h"
20 #include "llvm/IR/Attributes.h"
21 #include "llvm/IR/CallingConv.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/InstrTypes.h"
24 #include "llvm/MC/MCRegisterInfo.h"
25 #include "llvm/Support/Compiler.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Target/TargetOptions.h"
31 TargetFrameLowering::~TargetFrameLowering() = default;
33 bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
34 assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
35 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
36 !MF.getFunction().hasFnAttribute(Attribute::UWTable));
40 /// Returns the displacement from the frame register to the stack
41 /// frame of the specified index, along with the frame register used
42 /// (in output arg FrameReg). This is the default implementation which
43 /// is overridden for some targets.
44 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
46 Register &FrameReg) const {
47 const MachineFrameInfo &MFI = MF.getFrameInfo();
48 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
50 // By default, assume all frame indices are referenced via whatever
51 // getFrameRegister() says. The target can override this if it's doing
52 // something different.
53 FrameReg = RI->getFrameRegister(MF);
55 return MFI.getObjectOffset(FI) + MFI.getStackSize() -
56 getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
59 bool TargetFrameLowering::needsFrameIndexResolution(
60 const MachineFunction &MF) const {
61 return MF.getFrameInfo().hasStackObjects();
64 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
65 BitVector &CalleeSaves) const {
66 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
67 CalleeSaves.resize(TRI.getNumRegs());
69 const MachineFrameInfo &MFI = MF.getFrameInfo();
70 if (!MFI.isCalleeSavedInfoValid())
73 for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
74 CalleeSaves.set(Info.getReg());
77 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
79 RegScavenger *RS) const {
80 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
82 // Resize before the early returns. Some backends expect that
83 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
85 SavedRegs.resize(TRI.getNumRegs());
87 // When interprocedural register allocation is enabled caller saved registers
88 // are preferred over callee saved registers.
89 if (MF.getTarget().Options.EnableIPRA &&
90 isSafeForNoCSROpt(MF.getFunction()) &&
91 isProfitableForNoCSROpt(MF.getFunction()))
94 // Get the callee saved register list...
95 const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
97 // Early exit if there are no callee saved registers.
98 if (!CSRegs || CSRegs[0] == 0)
101 // In Naked functions we aren't going to save any registers.
102 if (MF.getFunction().hasFnAttribute(Attribute::Naked))
105 // Noreturn+nounwind functions never restore CSR, so no saves are needed.
106 // Purely noreturn functions may still return through throws, so those must
107 // save CSR for caller exception handlers.
109 // If the function uses longjmp to break out of its current path of
110 // execution we do not need the CSR spills either: setjmp stores all CSRs
111 // it was called with into the jmp_buf, which longjmp then restores.
112 if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
113 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
114 !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
115 enableCalleeSaveSkip(MF))
118 // Functions which call __builtin_unwind_init get all their registers saved.
119 bool CallsUnwindInit = MF.callsUnwindInit();
120 const MachineRegisterInfo &MRI = MF.getRegInfo();
121 for (unsigned i = 0; CSRegs[i]; ++i) {
122 unsigned Reg = CSRegs[i];
123 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
128 unsigned TargetFrameLowering::getStackAlignmentSkew(
129 const MachineFunction &MF) const {
130 // When HHVM function is called, the stack is skewed as the return address
131 // is removed from the stack before we enter the function.
132 if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
133 return MF.getTarget().getAllocaPointerSize();
138 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
139 if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
140 !F.hasFnAttribute(Attribute::NoRecurse))
142 // Function should not be optimized as tail call.
143 for (const User *U : F.users())
144 if (auto *CB = dyn_cast<CallBase>(U))
145 if (CB->isTailCall())
150 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
151 llvm_unreachable("getInitialCFAOffset() not implemented!");
155 TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
156 llvm_unreachable("getInitialCFARegister() not implemented!");
159 TargetFrameLowering::DwarfFrameBase
160 TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
161 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
162 return DwarfFrameBase{DwarfFrameBase::Register, {RI->getFrameRegister(MF)}};