lib/CodeGen/TargetFrameLoweringImpl.cpp

   1 //===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
   2 //
   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
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Implements the layout of a stack frame on the target machine.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  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/CallingConv.h"
  22 #include "llvm/IR/Function.h"
  23 #include "llvm/MC/MCRegisterInfo.h"
  24 #include "llvm/Support/Compiler.h"
  25 #include "llvm/Target/TargetMachine.h"
  26 #include "llvm/Target/TargetOptions.h"
  27
  28 using namespace llvm;
  29
  30 TargetFrameLowering::~TargetFrameLowering() = default;
  31
  32 bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
  33   assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
  34          MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
  35          !MF.getFunction().hasFnAttribute(Attribute::UWTable));
  36   return false;
  37 }
  38
  39 /// Returns the displacement from the frame register to the stack
  40 /// frame of the specified index, along with the frame register used
  41 /// (in output arg FrameReg). This is the default implementation which
  42 /// is overridden for some targets.
  43 int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
  44                                              int FI, unsigned &FrameReg) const {
  45   const MachineFrameInfo &MFI = MF.getFrameInfo();
  46   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
  47
  48   // By default, assume all frame indices are referenced via whatever
  49   // getFrameRegister() says. The target can override this if it's doing
  50   // something different.
  51   FrameReg = RI->getFrameRegister(MF);
  52
  53   return MFI.getObjectOffset(FI) + MFI.getStackSize() -
  54          getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
  55 }
  56
  57 bool TargetFrameLowering::needsFrameIndexResolution(
  58     const MachineFunction &MF) const {
  59   return MF.getFrameInfo().hasStackObjects();
  60 }
  61
  62 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
  63                                                BitVector &SavedRegs,
  64                                                RegScavenger *RS) const {
  65   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
  66
  67   // Resize before the early returns. Some backends expect that
  68   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
  69   // saved registers.
  70   SavedRegs.resize(TRI.getNumRegs());
  71
  72   // When interprocedural register allocation is enabled caller saved registers
  73   // are preferred over callee saved registers.
  74   if (MF.getTarget().Options.EnableIPRA &&
  75       isSafeForNoCSROpt(MF.getFunction()) &&
  76       isProfitableForNoCSROpt(MF.getFunction()))
  77     return;
  78
  79   // Get the callee saved register list...
  80   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
  81
  82   // Early exit if there are no callee saved registers.
  83   if (!CSRegs || CSRegs[0] == 0)
  84     return;
  85
  86   // In Naked functions we aren't going to save any registers.
  87   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
  88     return;
  89
  90   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
  91   // Purely noreturn functions may still return through throws, so those must
  92   // save CSR for caller exception handlers.
  93   //
  94   // If the function uses longjmp to break out of its current path of
  95   // execution we do not need the CSR spills either: setjmp stores all CSRs
  96   // it was called with into the jmp_buf, which longjmp then restores.
  97   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
  98         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
  99         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
 100         enableCalleeSaveSkip(MF))
 101     return;
 102
 103   // Functions which call __builtin_unwind_init get all their registers saved.
 104   bool CallsUnwindInit = MF.callsUnwindInit();
 105   const MachineRegisterInfo &MRI = MF.getRegInfo();
 106   for (unsigned i = 0; CSRegs[i]; ++i) {
 107     unsigned Reg = CSRegs[i];
 108     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
 109       SavedRegs.set(Reg);
 110   }
 111 }
 112
 113 unsigned TargetFrameLowering::getStackAlignmentSkew(
 114     const MachineFunction &MF) const {
 115   // When HHVM function is called, the stack is skewed as the return address
 116   // is removed from the stack before we enter the function.
 117   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
 118     return MF.getTarget().getAllocaPointerSize();
 119
 120   return 0;
 121 }
 122
 123 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
 124   llvm_unreachable("getInitialCFAOffset() not implemented!");
 125 }
 126
 127 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
 128     const {
 129   llvm_unreachable("getInitialCFARegister() not implemented!");
 130 }