1 //===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
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
7 //===----------------------------------------------------------------------===//
9 // Implements the layout of a stack frame on the target machine.
11 //===----------------------------------------------------------------------===//
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/CallSite.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"
31 TargetFrameLowering::~TargetFrameLowering() = default;
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));
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();
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);
54 return MFI.getObjectOffset(FI) + MFI.getStackSize() -
55 getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
58 bool TargetFrameLowering::needsFrameIndexResolution(
59 const MachineFunction &MF) const {
60 return MF.getFrameInfo().hasStackObjects();
63 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
64 BitVector &CalleeSaves) const {
65 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
66 CalleeSaves.resize(TRI.getNumRegs());
68 const MachineFrameInfo &MFI = MF.getFrameInfo();
69 if (!MFI.isCalleeSavedInfoValid())
72 for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
73 CalleeSaves.set(Info.getReg());
76 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
78 RegScavenger *RS) const {
79 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
81 // Resize before the early returns. Some backends expect that
82 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
84 SavedRegs.resize(TRI.getNumRegs());
86 // When interprocedural register allocation is enabled caller saved registers
87 // are preferred over callee saved registers.
88 if (MF.getTarget().Options.EnableIPRA &&
89 isSafeForNoCSROpt(MF.getFunction()) &&
90 isProfitableForNoCSROpt(MF.getFunction()))
93 // Get the callee saved register list...
94 const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
96 // Early exit if there are no callee saved registers.
97 if (!CSRegs || CSRegs[0] == 0)
100 // In Naked functions we aren't going to save any registers.
101 if (MF.getFunction().hasFnAttribute(Attribute::Naked))
104 // Noreturn+nounwind functions never restore CSR, so no saves are needed.
105 // Purely noreturn functions may still return through throws, so those must
106 // save CSR for caller exception handlers.
108 // If the function uses longjmp to break out of its current path of
109 // execution we do not need the CSR spills either: setjmp stores all CSRs
110 // it was called with into the jmp_buf, which longjmp then restores.
111 if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
112 MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
113 !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
114 enableCalleeSaveSkip(MF))
117 // Functions which call __builtin_unwind_init get all their registers saved.
118 bool CallsUnwindInit = MF.callsUnwindInit();
119 const MachineRegisterInfo &MRI = MF.getRegInfo();
120 for (unsigned i = 0; CSRegs[i]; ++i) {
121 unsigned Reg = CSRegs[i];
122 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
127 unsigned TargetFrameLowering::getStackAlignmentSkew(
128 const MachineFunction &MF) const {
129 // When HHVM function is called, the stack is skewed as the return address
130 // is removed from the stack before we enter the function.
131 if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
132 return MF.getTarget().getAllocaPointerSize();
137 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
138 if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
139 !F.hasFnAttribute(Attribute::NoRecurse))
141 // Function should not be optimized as tail call.
142 for (const User *U : F.users())
143 if (auto CS = ImmutableCallSite(U))
149 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
150 llvm_unreachable("getInitialCFAOffset() not implemented!");
153 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
155 llvm_unreachable("getInitialCFARegister() not implemented!");