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/Target/TargetFrameLowering.h"
16 #include "llvm/CodeGen/MachineFrameInfo.h"
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/CodeGen/MachineRegisterInfo.h"
20 #include "llvm/IR/CallingConv.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/Target/TargetRegisterInfo.h"
23 #include "llvm/Target/TargetSubtargetInfo.h"
24 #include <cstdlib>
25 using namespace llvm;
26
~TargetFrameLowering()27 TargetFrameLowering::~TargetFrameLowering() {
28 }
29
30 /// The default implementation just looks at attribute "no-frame-pointer-elim".
noFramePointerElim(const MachineFunction & MF) const31 bool TargetFrameLowering::noFramePointerElim(const MachineFunction &MF) const {
32 auto Attr = MF.getFunction()->getFnAttribute("no-frame-pointer-elim");
33 return Attr.getValueAsString() == "true";
34 }
35
36 /// Returns the displacement from the frame register to the stack
37 /// frame of the specified index, along with the frame register used
38 /// (in output arg FrameReg). This is the default implementation which
39 /// is overridden for some targets.
getFrameIndexReference(const MachineFunction & MF,int FI,unsigned & FrameReg) const40 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
41 int FI, unsigned &FrameReg) const {
42 const MachineFrameInfo *MFI = MF.getFrameInfo();
43 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
44
45 // By default, assume all frame indices are referenced via whatever
46 // getFrameRegister() says. The target can override this if it's doing
47 // something different.
48 FrameReg = RI->getFrameRegister(MF);
49
50 return MFI->getObjectOffset(FI) + MFI->getStackSize() -
51 getOffsetOfLocalArea() + MFI->getOffsetAdjustment();
52 }
53
needsFrameIndexResolution(const MachineFunction & MF) const54 bool TargetFrameLowering::needsFrameIndexResolution(
55 const MachineFunction &MF) const {
56 return MF.getFrameInfo()->hasStackObjects();
57 }
58
determineCalleeSaves(MachineFunction & MF,BitVector & SavedRegs,RegScavenger * RS) const59 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
60 BitVector &SavedRegs,
61 RegScavenger *RS) const {
62 // Get the callee saved register list...
63 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
64 const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(&MF);
65
66 // Early exit if there are no callee saved registers.
67 if (!CSRegs || CSRegs[0] == 0)
68 return;
69
70 SavedRegs.resize(TRI.getNumRegs());
71
72 // In Naked functions we aren't going to save any registers.
73 if (MF.getFunction()->hasFnAttribute(Attribute::Naked))
74 return;
75
76 // Functions which call __builtin_unwind_init get all their registers saved.
77 bool CallsUnwindInit = MF.getMMI().callsUnwindInit();
78 const MachineRegisterInfo &MRI = MF.getRegInfo();
79 for (unsigned i = 0; CSRegs[i]; ++i) {
80 unsigned Reg = CSRegs[i];
81 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
82 SavedRegs.set(Reg);
83 }
84 }
85
getStackAlignmentSkew(const MachineFunction & MF) const86 unsigned TargetFrameLowering::getStackAlignmentSkew(
87 const MachineFunction &MF) const {
88 // When HHVM function is called, the stack is skewed as the return address
89 // is removed from the stack before we enter the function.
90 if (LLVM_UNLIKELY(MF.getFunction()->getCallingConv() == CallingConv::HHVM))
91 return MF.getTarget().getPointerSize();
92
93 return 0;
94 }
95