1//===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
2//
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
6//
7//===----------------------------------------------------------------------===//
8//
9// Implements the layout of a stack frame on the target machine.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/ADT/BitVector.h"
14#include "llvm/CodeGen/MachineFrameInfo.h"
15#include "llvm/CodeGen/MachineFunction.h"
16#include "llvm/CodeGen/MachineRegisterInfo.h"
17#include "llvm/CodeGen/TargetFrameLowering.h"
18#include "llvm/CodeGen/TargetSubtargetInfo.h"
19#include "llvm/IR/Attributes.h"
20#include "llvm/IR/Function.h"
21#include "llvm/IR/InstrTypes.h"
22#include "llvm/MC/MCAsmInfo.h"
23#include "llvm/MC/MCRegisterInfo.h"
24#include "llvm/Support/Compiler.h"
25#include "llvm/Target/TargetMachine.h"
26#include "llvm/Target/TargetOptions.h"
27
28using namespace llvm;
29
30TargetFrameLowering::~TargetFrameLowering() = default;
31
32bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
33 assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
34 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
35 !MF.getFunction().hasFnAttribute(Attribute::UWTable));
36 return false;
37}
38
39bool TargetFrameLowering::enableCFIFixup(MachineFunction &MF) const {
40 return MF.needsFrameMoves() &&
41 !MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
42}
43
44/// Returns the displacement from the frame register to the stack
45/// frame of the specified index, along with the frame register used
46/// (in output arg FrameReg). This is the default implementation which
47/// is overridden for some targets.
48StackOffset
49TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
50 Register &FrameReg) const {
51 const MachineFrameInfo &MFI = MF.getFrameInfo();
52 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
53
54 // By default, assume all frame indices are referenced via whatever
55 // getFrameRegister() says. The target can override this if it's doing
56 // something different.
57 FrameReg = RI->getFrameRegister(MF);
58
59 return StackOffset::getFixed(Fixed: MFI.getObjectOffset(ObjectIdx: FI) + MFI.getStackSize() -
60 getOffsetOfLocalArea() +
61 MFI.getOffsetAdjustment());
62}
63
64bool TargetFrameLowering::needsFrameIndexResolution(
65 const MachineFunction &MF) const {
66 return MF.getFrameInfo().hasStackObjects();
67}
68
69void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
70 BitVector &CalleeSaves) const {
71 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
72 CalleeSaves.resize(N: TRI.getNumRegs());
73
74 const MachineFrameInfo &MFI = MF.getFrameInfo();
75 if (!MFI.isCalleeSavedInfoValid())
76 return;
77
78 for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
79 CalleeSaves.set(Info.getReg());
80}
81
82void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
83 BitVector &SavedRegs,
84 RegScavenger *RS) const {
85 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
86
87 // Resize before the early returns. Some backends expect that
88 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
89 // saved registers.
90 SavedRegs.resize(N: TRI.getNumRegs());
91
92 // When interprocedural register allocation is enabled caller saved registers
93 // are preferred over callee saved registers.
94 if (MF.getTarget().Options.EnableIPRA &&
95 isSafeForNoCSROpt(F: MF.getFunction()) &&
96 isProfitableForNoCSROpt(F: MF.getFunction()))
97 return;
98
99 // Get the callee saved register list...
100 const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
101
102 // Early exit if there are no callee saved registers.
103 if (!CSRegs || CSRegs[0] == 0)
104 return;
105
106 // In Naked functions we aren't going to save any registers.
107 if (MF.getFunction().hasFnAttribute(Attribute::Naked))
108 return;
109
110 // Noreturn+nounwind functions never restore CSR, so no saves are needed.
111 // Purely noreturn functions may still return through throws, so those must
112 // save CSR for caller exception handlers.
113 //
114 // If the function uses longjmp to break out of its current path of
115 // execution we do not need the CSR spills either: setjmp stores all CSRs
116 // it was called with into the jmp_buf, which longjmp then restores.
117 if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
118 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
119 !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
120 enableCalleeSaveSkip(MF))
121 return;
122
123 // Functions which call __builtin_unwind_init get all their registers saved.
124 bool CallsUnwindInit = MF.callsUnwindInit();
125 const MachineRegisterInfo &MRI = MF.getRegInfo();
126 for (unsigned i = 0; CSRegs[i]; ++i) {
127 unsigned Reg = CSRegs[i];
128 if (CallsUnwindInit || MRI.isPhysRegModified(PhysReg: Reg))
129 SavedRegs.set(Reg);
130 }
131}
132
133bool TargetFrameLowering::allocateScavengingFrameIndexesNearIncomingSP(
134 const MachineFunction &MF) const {
135 if (!hasFP(MF))
136 return false;
137
138 const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
139 return RegInfo->useFPForScavengingIndex(MF) &&
140 !RegInfo->hasStackRealignment(MF);
141}
142
143bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
144 if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
145 !F.hasFnAttribute(Attribute::NoRecurse))
146 return false;
147 // Function should not be optimized as tail call.
148 for (const User *U : F.users())
149 if (auto *CB = dyn_cast<CallBase>(Val: U))
150 if (CB->isTailCall())
151 return false;
152 return true;
153}
154
155int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
156 llvm_unreachable("getInitialCFAOffset() not implemented!");
157}
158
159Register
160TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
161 llvm_unreachable("getInitialCFARegister() not implemented!");
162}
163
164TargetFrameLowering::DwarfFrameBase
165TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
166 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
167 return DwarfFrameBase{.Kind: DwarfFrameBase::Register, .Location: {.Reg: RI->getFrameRegister(MF)}};
168}
169

source code of llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp