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/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"
28
29 using namespace llvm;
30
31 TargetFrameLowering::~TargetFrameLowering() = default;
32
enableCalleeSaveSkip(const MachineFunction & MF) const33 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));
37 return false;
38 }
39
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 StackOffset
getFrameIndexReference(const MachineFunction & MF,int FI,Register & FrameReg) const45 TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
46 Register &FrameReg) const {
47 const MachineFrameInfo &MFI = MF.getFrameInfo();
48 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
49
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);
54
55 return StackOffset::getFixed(MFI.getObjectOffset(FI) + MFI.getStackSize() -
56 getOffsetOfLocalArea() +
57 MFI.getOffsetAdjustment());
58 }
59
needsFrameIndexResolution(const MachineFunction & MF) const60 bool TargetFrameLowering::needsFrameIndexResolution(
61 const MachineFunction &MF) const {
62 return MF.getFrameInfo().hasStackObjects();
63 }
64
getCalleeSaves(const MachineFunction & MF,BitVector & CalleeSaves) const65 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
66 BitVector &CalleeSaves) const {
67 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
68 CalleeSaves.resize(TRI.getNumRegs());
69
70 const MachineFrameInfo &MFI = MF.getFrameInfo();
71 if (!MFI.isCalleeSavedInfoValid())
72 return;
73
74 for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
75 CalleeSaves.set(Info.getReg());
76 }
77
determineCalleeSaves(MachineFunction & MF,BitVector & SavedRegs,RegScavenger * RS) const78 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
79 BitVector &SavedRegs,
80 RegScavenger *RS) const {
81 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
82
83 // Resize before the early returns. Some backends expect that
84 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
85 // saved registers.
86 SavedRegs.resize(TRI.getNumRegs());
87
88 // When interprocedural register allocation is enabled caller saved registers
89 // are preferred over callee saved registers.
90 if (MF.getTarget().Options.EnableIPRA &&
91 isSafeForNoCSROpt(MF.getFunction()) &&
92 isProfitableForNoCSROpt(MF.getFunction()))
93 return;
94
95 // Get the callee saved register list...
96 const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
97
98 // Early exit if there are no callee saved registers.
99 if (!CSRegs || CSRegs[0] == 0)
100 return;
101
102 // In Naked functions we aren't going to save any registers.
103 if (MF.getFunction().hasFnAttribute(Attribute::Naked))
104 return;
105
106 // Noreturn+nounwind functions never restore CSR, so no saves are needed.
107 // Purely noreturn functions may still return through throws, so those must
108 // save CSR for caller exception handlers.
109 //
110 // If the function uses longjmp to break out of its current path of
111 // execution we do not need the CSR spills either: setjmp stores all CSRs
112 // it was called with into the jmp_buf, which longjmp then restores.
113 if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
114 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
115 !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
116 enableCalleeSaveSkip(MF))
117 return;
118
119 // Functions which call __builtin_unwind_init get all their registers saved.
120 bool CallsUnwindInit = MF.callsUnwindInit();
121 const MachineRegisterInfo &MRI = MF.getRegInfo();
122 for (unsigned i = 0; CSRegs[i]; ++i) {
123 unsigned Reg = CSRegs[i];
124 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
125 SavedRegs.set(Reg);
126 }
127 }
128
getStackAlignmentSkew(const MachineFunction & MF) const129 unsigned TargetFrameLowering::getStackAlignmentSkew(
130 const MachineFunction &MF) const {
131 // When HHVM function is called, the stack is skewed as the return address
132 // is removed from the stack before we enter the function.
133 if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
134 return MF.getTarget().getAllocaPointerSize();
135
136 return 0;
137 }
138
isSafeForNoCSROpt(const Function & F)139 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
140 if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
141 !F.hasFnAttribute(Attribute::NoRecurse))
142 return false;
143 // Function should not be optimized as tail call.
144 for (const User *U : F.users())
145 if (auto *CB = dyn_cast<CallBase>(U))
146 if (CB->isTailCall())
147 return false;
148 return true;
149 }
150
getInitialCFAOffset(const MachineFunction & MF) const151 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
152 llvm_unreachable("getInitialCFAOffset() not implemented!");
153 }
154
155 Register
getInitialCFARegister(const MachineFunction & MF) const156 TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
157 llvm_unreachable("getInitialCFARegister() not implemented!");
158 }
159
160 TargetFrameLowering::DwarfFrameBase
getDwarfFrameBase(const MachineFunction & MF) const161 TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
162 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
163 return DwarfFrameBase{DwarfFrameBase::Register, {RI->getFrameRegister(MF)}};
164 }
165