lib/CodeGen/TargetFrameLoweringImpl.cpp

   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 /// The default implementation just looks at attribute "no-frame-pointer-elim".
  34 bool TargetFrameLowering::noFramePointerElim(const MachineFunction &MF) const {
  35   auto Attr = MF.getFunction().getFnAttribute("no-frame-pointer-elim");
  36   return Attr.getValueAsString() == "true";
  37 }
  38
  39 bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
  40   assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
  41          MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
  42          !MF.getFunction().hasFnAttribute(Attribute::UWTable));
  43   return false;
  44 }
  45
  46 /// Returns the displacement from the frame register to the stack
  47 /// frame of the specified index, along with the frame register used
  48 /// (in output arg FrameReg). This is the default implementation which
  49 /// is overridden for some targets.
  50 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
  51                                              int FI, unsigned &FrameReg) const {
  52   const MachineFrameInfo &MFI = MF.getFrameInfo();
  53   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
  54
  55   // By default, assume all frame indices are referenced via whatever
  56   // getFrameRegister() says. The target can override this if it's doing
  57   // something different.
  58   FrameReg = RI->getFrameRegister(MF);
  59
  60   return MFI.getObjectOffset(FI) + MFI.getStackSize() -
  61          getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
  62 }
  63
  64 bool TargetFrameLowering::needsFrameIndexResolution(
  65     const MachineFunction &MF) const {
  66   return MF.getFrameInfo().hasStackObjects();
  67 }
  68
  69 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
  70                                                BitVector &SavedRegs,
  71                                                RegScavenger *RS) const {
  72   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
  73
  74   // Resize before the early returns. Some backends expect that
  75   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
  76   // saved registers.
  77   SavedRegs.resize(TRI.getNumRegs());
  78
  79   // When interprocedural register allocation is enabled caller saved registers
  80   // are preferred over callee saved registers.
  81   if (MF.getTarget().Options.EnableIPRA && isSafeForNoCSROpt(MF.getFunction()))
  82     return;
  83
  84   // Get the callee saved register list...
  85   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
  86
  87   // Early exit if there are no callee saved registers.
  88   if (!CSRegs || CSRegs[0] == 0)
  89     return;
  90
  91   // In Naked functions we aren't going to save any registers.
  92   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
  93     return;
  94
  95   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
  96   // Purely noreturn functions may still return through throws, so those must
  97   // save CSR for caller exception handlers.
  98   //
  99   // If the function uses longjmp to break out of its current path of
 100   // execution we do not need the CSR spills either: setjmp stores all CSRs
 101   // it was called with into the jmp_buf, which longjmp then restores.
 102   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
 103         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
 104         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
 105         enableCalleeSaveSkip(MF))
 106     return;
 107
 108   // Functions which call __builtin_unwind_init get all their registers saved.
 109   bool CallsUnwindInit = MF.callsUnwindInit();
 110   const MachineRegisterInfo &MRI = MF.getRegInfo();
 111   for (unsigned i = 0; CSRegs[i]; ++i) {
 112     unsigned Reg = CSRegs[i];
 113     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
 114       SavedRegs.set(Reg);
 115   }
 116 }
 117
 118 unsigned TargetFrameLowering::getStackAlignmentSkew(
 119     const MachineFunction &MF) const {
 120   // When HHVM function is called, the stack is skewed as the return address
 121   // is removed from the stack before we enter the function.
 122   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
 123     return MF.getTarget().getAllocaPointerSize();
 124
 125   return 0;
 126 }
 127
 128 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
 129   llvm_unreachable("getInitialCFAOffset() not implemented!");
 130 }
 131
 132 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
 133     const {
 134   llvm_unreachable("getInitialCFARegister() not implemented!");
 135 }