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      1 //===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
      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 // This file is a copy of the generic LLVM PrologEpilogInserter pass, modified
     11 // to remove unneeded functionality and to handle virtual registers. Most code
     12 // here is a copy of PrologEpilogInserter.cpp.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #include "NVPTX.h"
     17 #include "llvm/CodeGen/MachineFrameInfo.h"
     18 #include "llvm/CodeGen/MachineFunction.h"
     19 #include "llvm/CodeGen/MachineFunctionPass.h"
     20 #include "llvm/Pass.h"
     21 #include "llvm/Support/Debug.h"
     22 #include "llvm/Support/raw_ostream.h"
     23 #include "llvm/Target/TargetFrameLowering.h"
     24 #include "llvm/Target/TargetRegisterInfo.h"
     25 #include "llvm/Target/TargetSubtargetInfo.h"
     26 
     27 using namespace llvm;
     28 
     29 #define DEBUG_TYPE "nvptx-prolog-epilog"
     30 
     31 namespace {
     32 class NVPTXPrologEpilogPass : public MachineFunctionPass {
     33 public:
     34   static char ID;
     35   NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
     36 
     37   bool runOnMachineFunction(MachineFunction &MF) override;
     38 
     39 private:
     40   void calculateFrameObjectOffsets(MachineFunction &Fn);
     41 };
     42 }
     43 
     44 MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
     45   return new NVPTXPrologEpilogPass();
     46 }
     47 
     48 char NVPTXPrologEpilogPass::ID = 0;
     49 
     50 bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
     51   const TargetSubtargetInfo &STI = MF.getSubtarget();
     52   const TargetFrameLowering &TFI = *STI.getFrameLowering();
     53   const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
     54   bool Modified = false;
     55 
     56   calculateFrameObjectOffsets(MF);
     57 
     58   for (MachineBasicBlock &MBB : MF) {
     59     for (MachineInstr &MI : MBB) {
     60       for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
     61         if (!MI.getOperand(i).isFI())
     62           continue;
     63         TRI.eliminateFrameIndex(MI, 0, i, nullptr);
     64         Modified = true;
     65       }
     66     }
     67   }
     68 
     69   // Add function prolog/epilog
     70   TFI.emitPrologue(MF, MF.front());
     71 
     72   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     73     // If last instruction is a return instruction, add an epilogue
     74     if (I->isReturnBlock())
     75       TFI.emitEpilogue(MF, *I);
     76   }
     77 
     78   return Modified;
     79 }
     80 
     81 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
     82 static inline void
     83 AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
     84                   bool StackGrowsDown, int64_t &Offset,
     85                   unsigned &MaxAlign) {
     86   // If the stack grows down, add the object size to find the lowest address.
     87   if (StackGrowsDown)
     88     Offset += MFI->getObjectSize(FrameIdx);
     89 
     90   unsigned Align = MFI->getObjectAlignment(FrameIdx);
     91 
     92   // If the alignment of this object is greater than that of the stack, then
     93   // increase the stack alignment to match.
     94   MaxAlign = std::max(MaxAlign, Align);
     95 
     96   // Adjust to alignment boundary.
     97   Offset = (Offset + Align - 1) / Align * Align;
     98 
     99   if (StackGrowsDown) {
    100     DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
    101     MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
    102   } else {
    103     DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
    104     MFI->setObjectOffset(FrameIdx, Offset);
    105     Offset += MFI->getObjectSize(FrameIdx);
    106   }
    107 }
    108 
    109 void
    110 NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
    111   const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
    112   const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
    113 
    114   bool StackGrowsDown =
    115     TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
    116 
    117   // Loop over all of the stack objects, assigning sequential addresses...
    118   MachineFrameInfo *MFI = Fn.getFrameInfo();
    119 
    120   // Start at the beginning of the local area.
    121   // The Offset is the distance from the stack top in the direction
    122   // of stack growth -- so it's always nonnegative.
    123   int LocalAreaOffset = TFI.getOffsetOfLocalArea();
    124   if (StackGrowsDown)
    125     LocalAreaOffset = -LocalAreaOffset;
    126   assert(LocalAreaOffset >= 0
    127          && "Local area offset should be in direction of stack growth");
    128   int64_t Offset = LocalAreaOffset;
    129 
    130   // If there are fixed sized objects that are preallocated in the local area,
    131   // non-fixed objects can't be allocated right at the start of local area.
    132   // We currently don't support filling in holes in between fixed sized
    133   // objects, so we adjust 'Offset' to point to the end of last fixed sized
    134   // preallocated object.
    135   for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
    136     int64_t FixedOff;
    137     if (StackGrowsDown) {
    138       // The maximum distance from the stack pointer is at lower address of
    139       // the object -- which is given by offset. For down growing stack
    140       // the offset is negative, so we negate the offset to get the distance.
    141       FixedOff = -MFI->getObjectOffset(i);
    142     } else {
    143       // The maximum distance from the start pointer is at the upper
    144       // address of the object.
    145       FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
    146     }
    147     if (FixedOff > Offset) Offset = FixedOff;
    148   }
    149 
    150   // NOTE: We do not have a call stack
    151 
    152   unsigned MaxAlign = MFI->getMaxAlignment();
    153 
    154   // No scavenger
    155 
    156   // FIXME: Once this is working, then enable flag will change to a target
    157   // check for whether the frame is large enough to want to use virtual
    158   // frame index registers. Functions which don't want/need this optimization
    159   // will continue to use the existing code path.
    160   if (MFI->getUseLocalStackAllocationBlock()) {
    161     unsigned Align = MFI->getLocalFrameMaxAlign();
    162 
    163     // Adjust to alignment boundary.
    164     Offset = (Offset + Align - 1) / Align * Align;
    165 
    166     DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
    167 
    168     // Resolve offsets for objects in the local block.
    169     for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
    170       std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
    171       int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
    172       DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
    173             FIOffset << "]\n");
    174       MFI->setObjectOffset(Entry.first, FIOffset);
    175     }
    176     // Allocate the local block
    177     Offset += MFI->getLocalFrameSize();
    178 
    179     MaxAlign = std::max(Align, MaxAlign);
    180   }
    181 
    182   // No stack protector
    183 
    184   // Then assign frame offsets to stack objects that are not used to spill
    185   // callee saved registers.
    186   for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
    187     if (MFI->isObjectPreAllocated(i) &&
    188         MFI->getUseLocalStackAllocationBlock())
    189       continue;
    190     if (MFI->isDeadObjectIndex(i))
    191       continue;
    192 
    193     AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
    194   }
    195 
    196   // No scavenger
    197 
    198   if (!TFI.targetHandlesStackFrameRounding()) {
    199     // If we have reserved argument space for call sites in the function
    200     // immediately on entry to the current function, count it as part of the
    201     // overall stack size.
    202     if (MFI->adjustsStack() && TFI.hasReservedCallFrame(Fn))
    203       Offset += MFI->getMaxCallFrameSize();
    204 
    205     // Round up the size to a multiple of the alignment.  If the function has
    206     // any calls or alloca's, align to the target's StackAlignment value to
    207     // ensure that the callee's frame or the alloca data is suitably aligned;
    208     // otherwise, for leaf functions, align to the TransientStackAlignment
    209     // value.
    210     unsigned StackAlign;
    211     if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
    212         (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
    213       StackAlign = TFI.getStackAlignment();
    214     else
    215       StackAlign = TFI.getTransientStackAlignment();
    216 
    217     // If the frame pointer is eliminated, all frame offsets will be relative to
    218     // SP not FP. Align to MaxAlign so this works.
    219     StackAlign = std::max(StackAlign, MaxAlign);
    220     unsigned AlignMask = StackAlign - 1;
    221     Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
    222   }
    223 
    224   // Update frame info to pretend that this is part of the stack...
    225   int64_t StackSize = Offset - LocalAreaOffset;
    226   MFI->setStackSize(StackSize);
    227 }
    228