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/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/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 /// Returns the displacement from the frame register to the stack
40 /// frame of the specified index, along with the frame register used
41 /// (in output arg FrameReg). This is the default implementation which
42 /// is overridden for some targets.
43 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
44                                              int FI, unsigned &FrameReg) const {
45   const MachineFrameInfo &MFI = MF.getFrameInfo();
46   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
47 
48   // By default, assume all frame indices are referenced via whatever
49   // getFrameRegister() says. The target can override this if it's doing
50   // something different.
51   FrameReg = RI->getFrameRegister(MF);
52 
53   return MFI.getObjectOffset(FI) + MFI.getStackSize() -
54          getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
55 }
56 
57 bool TargetFrameLowering::needsFrameIndexResolution(
58     const MachineFunction &MF) const {
59   return MF.getFrameInfo().hasStackObjects();
60 }
61 
62 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
63                                          BitVector &CalleeSaves) const {
64   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
65   CalleeSaves.resize(TRI.getNumRegs());
66 
67   const MachineFrameInfo &MFI = MF.getFrameInfo();
68   if (!MFI.isCalleeSavedInfoValid())
69     return;
70 
71   for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
72     CalleeSaves.set(Info.getReg());
73 }
74 
75 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
76                                                BitVector &SavedRegs,
77                                                RegScavenger *RS) const {
78   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
79 
80   // Resize before the early returns. Some backends expect that
81   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
82   // saved registers.
83   SavedRegs.resize(TRI.getNumRegs());
84 
85   // When interprocedural register allocation is enabled caller saved registers
86   // are preferred over callee saved registers.
87   if (MF.getTarget().Options.EnableIPRA &&
88       isSafeForNoCSROpt(MF.getFunction()) &&
89       isProfitableForNoCSROpt(MF.getFunction()))
90     return;
91 
92   // Get the callee saved register list...
93   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
94 
95   // Early exit if there are no callee saved registers.
96   if (!CSRegs || CSRegs[0] == 0)
97     return;
98 
99   // In Naked functions we aren't going to save any registers.
100   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
101     return;
102 
103   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
104   // Purely noreturn functions may still return through throws, so those must
105   // save CSR for caller exception handlers.
106   //
107   // If the function uses longjmp to break out of its current path of
108   // execution we do not need the CSR spills either: setjmp stores all CSRs
109   // it was called with into the jmp_buf, which longjmp then restores.
110   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
111         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
112         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
113         enableCalleeSaveSkip(MF))
114     return;
115 
116   // Functions which call __builtin_unwind_init get all their registers saved.
117   bool CallsUnwindInit = MF.callsUnwindInit();
118   const MachineRegisterInfo &MRI = MF.getRegInfo();
119   for (unsigned i = 0; CSRegs[i]; ++i) {
120     unsigned Reg = CSRegs[i];
121     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
122       SavedRegs.set(Reg);
123   }
124 }
125 
126 unsigned TargetFrameLowering::getStackAlignmentSkew(
127     const MachineFunction &MF) const {
128   // When HHVM function is called, the stack is skewed as the return address
129   // is removed from the stack before we enter the function.
130   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
131     return MF.getTarget().getAllocaPointerSize();
132 
133   return 0;
134 }
135 
136 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
137   llvm_unreachable("getInitialCFAOffset() not implemented!");
138 }
139 
140 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
141     const {
142   llvm_unreachable("getInitialCFARegister() not implemented!");
143 }
144