1 //===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Implements the layout of a stack frame on the target machine.
11 //
12 //===----------------------------------------------------------------------===//
13 
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/TargetFrameLowering.h"
19 #include "llvm/CodeGen/TargetRegisterInfo.h"
20 #include "llvm/CodeGen/TargetSubtargetInfo.h"
21 #include "llvm/IR/Attributes.h"
22 #include "llvm/IR/CallingConv.h"
23 #include "llvm/IR/Function.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 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
45                                              int FI, unsigned &FrameReg) const {
46   const MachineFrameInfo &MFI = MF.getFrameInfo();
47   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
48 
49   // By default, assume all frame indices are referenced via whatever
50   // getFrameRegister() says. The target can override this if it's doing
51   // something different.
52   FrameReg = RI->getFrameRegister(MF);
53 
54   return MFI.getObjectOffset(FI) + MFI.getStackSize() -
55          getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
56 }
57 
58 bool TargetFrameLowering::needsFrameIndexResolution(
59     const MachineFunction &MF) const {
60   return MF.getFrameInfo().hasStackObjects();
61 }
62 
63 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
64                                                BitVector &SavedRegs,
65                                                RegScavenger *RS) const {
66   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
67 
68   // Resize before the early returns. Some backends expect that
69   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
70   // saved registers.
71   SavedRegs.resize(TRI.getNumRegs());
72 
73   // When interprocedural register allocation is enabled caller saved registers
74   // are preferred over callee saved registers.
75   if (MF.getTarget().Options.EnableIPRA && isSafeForNoCSROpt(MF.getFunction()))
76     return;
77 
78   // Get the callee saved register list...
79   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
80 
81   // Early exit if there are no callee saved registers.
82   if (!CSRegs || CSRegs[0] == 0)
83     return;
84 
85   // In Naked functions we aren't going to save any registers.
86   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
87     return;
88 
89   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
90   // Purely noreturn functions may still return through throws, so those must
91   // save CSR for caller exception handlers.
92   //
93   // If the function uses longjmp to break out of its current path of
94   // execution we do not need the CSR spills either: setjmp stores all CSRs
95   // it was called with into the jmp_buf, which longjmp then restores.
96   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
97         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
98         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
99         enableCalleeSaveSkip(MF))
100     return;
101 
102   // Functions which call __builtin_unwind_init get all their registers saved.
103   bool CallsUnwindInit = MF.callsUnwindInit();
104   const MachineRegisterInfo &MRI = MF.getRegInfo();
105   for (unsigned i = 0; CSRegs[i]; ++i) {
106     unsigned Reg = CSRegs[i];
107     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
108       SavedRegs.set(Reg);
109   }
110 }
111 
112 unsigned TargetFrameLowering::getStackAlignmentSkew(
113     const MachineFunction &MF) const {
114   // When HHVM function is called, the stack is skewed as the return address
115   // is removed from the stack before we enter the function.
116   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
117     return MF.getTarget().getAllocaPointerSize();
118 
119   return 0;
120 }
121 
122 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
123   llvm_unreachable("getInitialCFAOffset() not implemented!");
124 }
125 
126 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
127     const {
128   llvm_unreachable("getInitialCFARegister() not implemented!");
129 }