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
28 using namespace llvm;
29
30 TargetFrameLowering::~TargetFrameLowering() = default;
31
enableCalleeSaveSkip(const MachineFunction & MF) const32 bool 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
enableCFIFixup(MachineFunction & MF) const39 bool 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.
48 StackOffset
getFrameIndexReference(const MachineFunction & MF,int FI,Register & FrameReg) const49 TargetFrameLowering::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(MFI.getObjectOffset(FI) + MFI.getStackSize() -
60 getOffsetOfLocalArea() +
61 MFI.getOffsetAdjustment());
62 }
63
64 /// Returns the offset from the stack pointer to the slot of the specified
65 /// index. This function serves to provide a comparable offset from a single
66 /// reference point (the value of the stack-pointer at function entry) that can
67 /// be used for analysis. This is the default implementation using
68 /// MachineFrameInfo offsets.
69 StackOffset
getFrameIndexReferenceFromSP(const MachineFunction & MF,int FI) const70 TargetFrameLowering::getFrameIndexReferenceFromSP(const MachineFunction &MF,
71 int FI) const {
72 // To display the true offset from SP, we need to subtract the offset to the
73 // local area from MFI's ObjectOffset.
74 return StackOffset::getFixed(MF.getFrameInfo().getObjectOffset(FI) -
75 getOffsetOfLocalArea());
76 }
77
needsFrameIndexResolution(const MachineFunction & MF) const78 bool TargetFrameLowering::needsFrameIndexResolution(
79 const MachineFunction &MF) const {
80 return MF.getFrameInfo().hasStackObjects();
81 }
82
getCalleeSaves(const MachineFunction & MF,BitVector & CalleeSaves) const83 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
84 BitVector &CalleeSaves) const {
85 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
86 CalleeSaves.resize(TRI.getNumRegs());
87
88 const MachineFrameInfo &MFI = MF.getFrameInfo();
89 if (!MFI.isCalleeSavedInfoValid())
90 return;
91
92 for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
93 CalleeSaves.set(Info.getReg());
94 }
95
determineCalleeSaves(MachineFunction & MF,BitVector & SavedRegs,RegScavenger * RS) const96 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
97 BitVector &SavedRegs,
98 RegScavenger *RS) const {
99 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
100
101 // Resize before the early returns. Some backends expect that
102 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
103 // saved registers.
104 SavedRegs.resize(TRI.getNumRegs());
105
106 // When interprocedural register allocation is enabled caller saved registers
107 // are preferred over callee saved registers.
108 if (MF.getTarget().Options.EnableIPRA &&
109 isSafeForNoCSROpt(MF.getFunction()) &&
110 isProfitableForNoCSROpt(MF.getFunction()))
111 return;
112
113 // Get the callee saved register list...
114 const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
115
116 // Early exit if there are no callee saved registers.
117 if (!CSRegs || CSRegs[0] == 0)
118 return;
119
120 // In Naked functions we aren't going to save any registers.
121 if (MF.getFunction().hasFnAttribute(Attribute::Naked))
122 return;
123
124 // Noreturn+nounwind functions never restore CSR, so no saves are needed.
125 // Purely noreturn functions may still return through throws, so those must
126 // save CSR for caller exception handlers.
127 //
128 // If the function uses longjmp to break out of its current path of
129 // execution we do not need the CSR spills either: setjmp stores all CSRs
130 // it was called with into the jmp_buf, which longjmp then restores.
131 if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
132 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
133 !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
134 enableCalleeSaveSkip(MF))
135 return;
136
137 // Functions which call __builtin_unwind_init get all their registers saved.
138 bool CallsUnwindInit = MF.callsUnwindInit();
139 const MachineRegisterInfo &MRI = MF.getRegInfo();
140 for (unsigned i = 0; CSRegs[i]; ++i) {
141 unsigned Reg = CSRegs[i];
142 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
143 SavedRegs.set(Reg);
144 }
145 }
146
allocateScavengingFrameIndexesNearIncomingSP(const MachineFunction & MF) const147 bool TargetFrameLowering::allocateScavengingFrameIndexesNearIncomingSP(
148 const MachineFunction &MF) const {
149 if (!hasFP(MF))
150 return false;
151
152 const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
153 return RegInfo->useFPForScavengingIndex(MF) &&
154 !RegInfo->hasStackRealignment(MF);
155 }
156
isSafeForNoCSROpt(const Function & F)157 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
158 if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
159 !F.hasFnAttribute(Attribute::NoRecurse))
160 return false;
161 // Function should not be optimized as tail call.
162 for (const User *U : F.users())
163 if (auto *CB = dyn_cast<CallBase>(U))
164 if (CB->isTailCall())
165 return false;
166 return true;
167 }
168
getInitialCFAOffset(const MachineFunction & MF) const169 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
170 llvm_unreachable("getInitialCFAOffset() not implemented!");
171 }
172
173 Register
getInitialCFARegister(const MachineFunction & MF) const174 TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
175 llvm_unreachable("getInitialCFARegister() not implemented!");
176 }
177
178 TargetFrameLowering::DwarfFrameBase
getDwarfFrameBase(const MachineFunction & MF) const179 TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
180 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
181 return DwarfFrameBase{DwarfFrameBase::Register, {RI->getFrameRegister(MF)}};
182 }
183