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/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"
  28
  29 using namespace llvm;
  30
  31 TargetFrameLowering::~TargetFrameLowering() = default;
  32
  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));
  37   return false;
  38 }
  39
  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();
  48
  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);
  53
  54   return MFI.getObjectOffset(FI) + MFI.getStackSize() -
  55          getOffsetOfLocalArea() + MFI.getOffsetAdjustment();
  56 }
  57
  58 bool TargetFrameLowering::needsFrameIndexResolution(
  59     const MachineFunction &MF) const {
  60   return MF.getFrameInfo().hasStackObjects();
  61 }
  62
  63 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
  64                                                BitVector &SavedRegs,
  65                                                RegScavenger *RS) const {
  66   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
  67
  68   // Resize before the early returns. Some backends expect that
  69   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
  70   // saved registers.
  71   SavedRegs.resize(TRI.getNumRegs());
  72
  73   // When interprocedural register allocation is enabled caller saved registers
  74   // are preferred over callee saved registers.
  75   if (MF.getTarget().Options.EnableIPRA &&
  76       isSafeForNoCSROpt(MF.getFunction()) &&
  77       isProfitableForNoCSROpt(MF.getFunction()))
  78     return;
  79
  80   // Get the callee saved register list...
  81   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
  82
  83   // Early exit if there are no callee saved registers.
  84   if (!CSRegs || CSRegs[0] == 0)
  85     return;
  86
  87   // In Naked functions we aren't going to save any registers.
  88   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
  89     return;
  90
  91   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
  92   // Purely noreturn functions may still return through throws, so those must
  93   // save CSR for caller exception handlers.
  94   //
  95   // If the function uses longjmp to break out of its current path of
  96   // execution we do not need the CSR spills either: setjmp stores all CSRs
  97   // it was called with into the jmp_buf, which longjmp then restores.
  98   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
  99         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
 100         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
 101         enableCalleeSaveSkip(MF))
 102     return;
 103
 104   // Functions which call __builtin_unwind_init get all their registers saved.
 105   bool CallsUnwindInit = MF.callsUnwindInit();
 106   const MachineRegisterInfo &MRI = MF.getRegInfo();
 107   for (unsigned i = 0; CSRegs[i]; ++i) {
 108     unsigned Reg = CSRegs[i];
 109     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
 110       SavedRegs.set(Reg);
 111   }
 112 }
 113
 114 unsigned TargetFrameLowering::getStackAlignmentSkew(
 115     const MachineFunction &MF) const {
 116   // When HHVM function is called, the stack is skewed as the return address
 117   // is removed from the stack before we enter the function.
 118   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
 119     return MF.getTarget().getAllocaPointerSize();
 120
 121   return 0;
 122 }
 123
 124 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
 125   if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
 126       !F.hasFnAttribute(Attribute::NoRecurse))
 127     return false;
 128   // Function should not be optimized as tail call.
 129   for (const User *U : F.users())
 130     if (auto CS = ImmutableCallSite(U))
 131       if (CS.isTailCall())
 132         return false;
 133   return true;
 134 }
 135
 136 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
 137   llvm_unreachable("getInitialCFAOffset() not implemented!");
 138 }
 139
 140 unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
 141     const {
 142   llvm_unreachable("getInitialCFARegister() not implemented!");
 143 }