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 
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));
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
45 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 
60 bool TargetFrameLowering::needsFrameIndexResolution(
61     const MachineFunction &MF) const {
62   return MF.getFrameInfo().hasStackObjects();
63 }
64 
65 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 
78 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 
129 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 
139 bool TargetFrameLowering::allocateScavengingFrameIndexesNearIncomingSP(
140   const MachineFunction &MF) const {
141   if (!hasFP(MF))
142     return false;
143 
144   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
145   return RegInfo->useFPForScavengingIndex(MF) &&
146          !RegInfo->hasStackRealignment(MF);
147 }
148 
149 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
150   if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
151       !F.hasFnAttribute(Attribute::NoRecurse))
152     return false;
153   // Function should not be optimized as tail call.
154   for (const User *U : F.users())
155     if (auto *CB = dyn_cast<CallBase>(U))
156       if (CB->isTailCall())
157         return false;
158   return true;
159 }
160 
161 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
162   llvm_unreachable("getInitialCFAOffset() not implemented!");
163 }
164 
165 Register
166 TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
167   llvm_unreachable("getInitialCFARegister() not implemented!");
168 }
169 
170 TargetFrameLowering::DwarfFrameBase
171 TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
172   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
173   return DwarfFrameBase{DwarfFrameBase::Register, {RI->getFrameRegister(MF)}};
174 }
175