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/MachineModuleInfo.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/CodeGen/TargetPassConfig.h"
20 #include "llvm/IR/CallingConv.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/Target/TargetFrameLowering.h"
23 #include "llvm/Target/TargetRegisterInfo.h"
24 #include "llvm/Target/TargetSubtargetInfo.h"
25 #include <cstdlib>
26 using namespace llvm;
27
~TargetFrameLowering()28 TargetFrameLowering::~TargetFrameLowering() {
29 }
30
31 /// The default implementation just looks at attribute "no-frame-pointer-elim".
noFramePointerElim(const MachineFunction & MF) const32 bool TargetFrameLowering::noFramePointerElim(const MachineFunction &MF) const {
33 auto Attr = MF.getFunction()->getFnAttribute("no-frame-pointer-elim");
34 return Attr.getValueAsString() == "true";
35 }
36
37 /// Returns the displacement from the frame register to the stack
38 /// frame of the specified index, along with the frame register used
39 /// (in output arg FrameReg). This is the default implementation which
40 /// is overridden for some targets.
getFrameIndexReference(const MachineFunction & MF,int FI,unsigned & FrameReg) const41 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
42 int FI, unsigned &FrameReg) const {
43 const MachineFrameInfo *MFI = MF.getFrameInfo();
44 const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
45
46 // By default, assume all frame indices are referenced via whatever
47 // getFrameRegister() says. The target can override this if it's doing
48 // something different.
49 FrameReg = RI->getFrameRegister(MF);
50
51 return MFI->getObjectOffset(FI) + MFI->getStackSize() -
52 getOffsetOfLocalArea() + MFI->getOffsetAdjustment();
53 }
54
needsFrameIndexResolution(const MachineFunction & MF) const55 bool TargetFrameLowering::needsFrameIndexResolution(
56 const MachineFunction &MF) const {
57 return MF.getFrameInfo()->hasStackObjects();
58 }
59
determineCalleeSaves(MachineFunction & MF,BitVector & SavedRegs,RegScavenger * RS) const60 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
61 BitVector &SavedRegs,
62 RegScavenger *RS) const {
63 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
64
65 // Resize before the early returns. Some backends expect that
66 // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
67 // saved registers.
68 SavedRegs.resize(TRI.getNumRegs());
69
70 // When interprocedural register allocation is enabled caller saved registers
71 // are preferred over callee saved registers.
72 if (MF.getTarget().Options.EnableIPRA && isSafeForNoCSROpt(MF.getFunction()))
73 return;
74
75 // Get the callee saved register list...
76 const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(&MF);
77
78 // Early exit if there are no callee saved registers.
79 if (!CSRegs || CSRegs[0] == 0)
80 return;
81
82 // In Naked functions we aren't going to save any registers.
83 if (MF.getFunction()->hasFnAttribute(Attribute::Naked))
84 return;
85
86 // Functions which call __builtin_unwind_init get all their registers saved.
87 bool CallsUnwindInit = MF.getMMI().callsUnwindInit();
88 const MachineRegisterInfo &MRI = MF.getRegInfo();
89 for (unsigned i = 0; CSRegs[i]; ++i) {
90 unsigned Reg = CSRegs[i];
91 if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
92 SavedRegs.set(Reg);
93 }
94 }
95
getStackAlignmentSkew(const MachineFunction & MF) const96 unsigned TargetFrameLowering::getStackAlignmentSkew(
97 const MachineFunction &MF) const {
98 // When HHVM function is called, the stack is skewed as the return address
99 // is removed from the stack before we enter the function.
100 if (LLVM_UNLIKELY(MF.getFunction()->getCallingConv() == CallingConv::HHVM))
101 return MF.getTarget().getPointerSize();
102
103 return 0;
104 }
105