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 | |
32 | 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 | |
39 | 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 |
49 | 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(Fixed: MFI.getObjectOffset(ObjectIdx: FI) + MFI.getStackSize() - |
60 | getOffsetOfLocalArea() + |
61 | MFI.getOffsetAdjustment()); |
62 | } |
63 | |
64 | bool TargetFrameLowering::needsFrameIndexResolution( |
65 | const MachineFunction &MF) const { |
66 | return MF.getFrameInfo().hasStackObjects(); |
67 | } |
68 | |
69 | void 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 | |
82 | void 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 | |
133 | bool 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 | |
143 | bool 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 | |
155 | int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const { |
156 | llvm_unreachable("getInitialCFAOffset() not implemented!" ); |
157 | } |
158 | |
159 | Register |
160 | TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const { |
161 | llvm_unreachable("getInitialCFARegister() not implemented!" ); |
162 | } |
163 | |
164 | TargetFrameLowering::DwarfFrameBase |
165 | TargetFrameLowering::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 | |