llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp

   1 //===-- SystemZSelectionDAGInfo.cpp - SystemZ SelectionDAG Info -----------===//
   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 // This file implements the SystemZSelectionDAGInfo class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "SystemZTargetMachine.h"
  14 #include "llvm/CodeGen/SelectionDAG.h"
  15
  16 using namespace llvm;
  17
  18 #define DEBUG_TYPE "systemz-selectiondag-info"
  19
  20 // Decide whether it is best to use a loop or straight-line code for
  21 // a block operation of Size bytes with source address Src and destination
  22 // address Dest.  Sequence is the opcode to use for straight-line code
  23 // (such as MVC) and Loop is the opcode to use for loops (such as MVC_LOOP).
  24 // Return the chain for the completed operation.
  25 static SDValue emitMemMem(SelectionDAG &DAG, const SDLoc &DL, unsigned Sequence,
  26                           unsigned Loop, SDValue Chain, SDValue Dst,
  27                           SDValue Src, uint64_t Size) {
  28   EVT PtrVT = Src.getValueType();
  29   // The heuristic we use is to prefer loops for anything that would
  30   // require 7 or more MVCs.  With these kinds of sizes there isn't
  31   // much to choose between straight-line code and looping code,
  32   // since the time will be dominated by the MVCs themselves.
  33   // However, the loop has 4 or 5 instructions (depending on whether
  34   // the base addresses can be proved equal), so there doesn't seem
  35   // much point using a loop for 5 * 256 bytes or fewer.  Anything in
  36   // the range (5 * 256, 6 * 256) will need another instruction after
  37   // the loop, so it doesn't seem worth using a loop then either.
  38   // The next value up, 6 * 256, can be implemented in the same
  39   // number of straight-line MVCs as 6 * 256 - 1.
  40   if (Size > 6 * 256)
  41     return DAG.getNode(Loop, DL, MVT::Other, Chain, Dst, Src,
  42                        DAG.getConstant(Size, DL, PtrVT),
  43                        DAG.getConstant(Size / 256, DL, PtrVT));
  44   return DAG.getNode(Sequence, DL, MVT::Other, Chain, Dst, Src,
  45                      DAG.getConstant(Size, DL, PtrVT));
  46 }
  47
  48 SDValue SystemZSelectionDAGInfo::EmitTargetCodeForMemcpy(
  49     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dst, SDValue Src,
  50     SDValue Size, Align Alignment, bool IsVolatile, bool AlwaysInline,
  51     MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) const {
  52   if (IsVolatile)
  53     return SDValue();
  54
  55   if (auto *CSize = dyn_cast<ConstantSDNode>(Size))
  56     return emitMemMem(DAG, DL, SystemZISD::MVC, SystemZISD::MVC_LOOP,
  57                       Chain, Dst, Src, CSize->getZExtValue());
  58   return SDValue();
  59 }
  60
  61 // Handle a memset of 1, 2, 4 or 8 bytes with the operands given by
  62 // Chain, Dst, ByteVal and Size.  These cases are expected to use
  63 // MVI, MVHHI, MVHI and MVGHI respectively.
  64 static SDValue memsetStore(SelectionDAG &DAG, const SDLoc &DL, SDValue Chain,
  65                            SDValue Dst, uint64_t ByteVal, uint64_t Size,
  66                            unsigned Align, MachinePointerInfo DstPtrInfo) {
  67   uint64_t StoreVal = ByteVal;
  68   for (unsigned I = 1; I < Size; ++I)
  69     StoreVal |= ByteVal << (I * 8);
  70   return DAG.getStore(
  71       Chain, DL, DAG.getConstant(StoreVal, DL, MVT::getIntegerVT(Size * 8)),
  72       Dst, DstPtrInfo, Align);
  73 }
  74
  75 SDValue SystemZSelectionDAGInfo::EmitTargetCodeForMemset(
  76     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dst,
  77     SDValue Byte, SDValue Size, Align Alignment, bool IsVolatile,
  78     MachinePointerInfo DstPtrInfo) const {
  79   EVT PtrVT = Dst.getValueType();
  80
  81   if (IsVolatile)
  82     return SDValue();
  83
  84   auto *CByte = dyn_cast<ConstantSDNode>(Byte);
  85   if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
  86     uint64_t Bytes = CSize->getZExtValue();
  87     if (Bytes == 0)
  88       return SDValue();
  89     if (CByte) {
  90       // Handle cases that can be done using at most two of
  91       // MVI, MVHI, MVHHI and MVGHI.  The latter two can only be
  92       // used if ByteVal is all zeros or all ones; in other casees,
  93       // we can move at most 2 halfwords.
  94       uint64_t ByteVal = CByte->getZExtValue();
  95       if (ByteVal == 0 || ByteVal == 255 ?
  96           Bytes <= 16 && countPopulation(Bytes) <= 2 :
  97           Bytes <= 4) {
  98         unsigned Size1 = Bytes == 16 ? 8 : 1 << findLastSet(Bytes);
  99         unsigned Size2 = Bytes - Size1;
 100         SDValue Chain1 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size1,
 101                                      Alignment.value(), DstPtrInfo);
 102         if (Size2 == 0)
 103           return Chain1;
 104         Dst = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
 105                           DAG.getConstant(Size1, DL, PtrVT));
 106         DstPtrInfo = DstPtrInfo.getWithOffset(Size1);
 107         SDValue Chain2 = memsetStore(
 108             DAG, DL, Chain, Dst, ByteVal, Size2,
 109             std::min((unsigned)Alignment.value(), Size1), DstPtrInfo);
 110         return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
 111       }
 112     } else {
 113       // Handle one and two bytes using STC.
 114       if (Bytes <= 2) {
 115         SDValue Chain1 =
 116             DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Alignment);
 117         if (Bytes == 1)
 118           return Chain1;
 119         SDValue Dst2 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
 120                                    DAG.getConstant(1, DL, PtrVT));
 121         SDValue Chain2 = DAG.getStore(Chain, DL, Byte, Dst2,
 122                                       DstPtrInfo.getWithOffset(1), Align(1));
 123         return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
 124       }
 125     }
 126     assert(Bytes >= 2 && "Should have dealt with 0- and 1-byte cases already");
 127
 128     // Handle the special case of a memset of 0, which can use XC.
 129     if (CByte && CByte->getZExtValue() == 0)
 130       return emitMemMem(DAG, DL, SystemZISD::XC, SystemZISD::XC_LOOP,
 131                         Chain, Dst, Dst, Bytes);
 132
 133     // Copy the byte to the first location and then use MVC to copy
 134     // it to the rest.
 135     Chain = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Alignment);
 136     SDValue DstPlus1 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
 137                                    DAG.getConstant(1, DL, PtrVT));
 138     return emitMemMem(DAG, DL, SystemZISD::MVC, SystemZISD::MVC_LOOP,
 139                       Chain, DstPlus1, Dst, Bytes - 1);
 140   }
 141
 142   // Variable length
 143   if (CByte && CByte->getZExtValue() == 0) {
 144     // Handle the special case of a variable length memset of 0 with XC.
 145     SDValue LenMinus1 = DAG.getNode(ISD::ADD, DL, MVT::i64,
 146                                     DAG.getZExtOrTrunc(Size, DL, MVT::i64),
 147                                     DAG.getConstant(-1, DL, MVT::i64));
 148     SDValue TripC = DAG.getNode(ISD::SRL, DL, MVT::i64, LenMinus1,
 149                                 DAG.getConstant(8, DL, MVT::i64));
 150     return DAG.getNode(SystemZISD::XC_LOOP, DL, MVT::Other, Chain, Dst, Dst,
 151                        LenMinus1, TripC);
 152   }
 153   return SDValue();
 154 }
 155
 156 // Use CLC to compare [Src1, Src1 + Size) with [Src2, Src2 + Size),
 157 // deciding whether to use a loop or straight-line code.
 158 static SDValue emitCLC(SelectionDAG &DAG, const SDLoc &DL, SDValue Chain,
 159                        SDValue Src1, SDValue Src2, uint64_t Size) {
 160   SDVTList VTs = DAG.getVTList(MVT::i32, MVT::Other);
 161   EVT PtrVT = Src1.getValueType();
 162   // A two-CLC sequence is a clear win over a loop, not least because it
 163   // needs only one branch.  A three-CLC sequence needs the same number
 164   // of branches as a loop (i.e. 2), but is shorter.  That brings us to
 165   // lengths greater than 768 bytes.  It seems relatively likely that
 166   // a difference will be found within the first 768 bytes, so we just
 167   // optimize for the smallest number of branch instructions, in order
 168   // to avoid polluting the prediction buffer too much.  A loop only ever
 169   // needs 2 branches, whereas a straight-line sequence would need 3 or more.
 170   if (Size > 3 * 256)
 171     return DAG.getNode(SystemZISD::CLC_LOOP, DL, VTs, Chain, Src1, Src2,
 172                        DAG.getConstant(Size, DL, PtrVT),
 173                        DAG.getConstant(Size / 256, DL, PtrVT));
 174   return DAG.getNode(SystemZISD::CLC, DL, VTs, Chain, Src1, Src2,
 175                      DAG.getConstant(Size, DL, PtrVT));
 176 }
 177
 178 // Convert the current CC value into an integer that is 0 if CC == 0,
 179 // greater than zero if CC == 1 and less than zero if CC >= 2.
 180 // The sequence starts with IPM, which puts CC into bits 29 and 28
 181 // of an integer and clears bits 30 and 31.
 182 static SDValue addIPMSequence(const SDLoc &DL, SDValue CCReg,
 183                               SelectionDAG &DAG) {
 184   SDValue IPM = DAG.getNode(SystemZISD::IPM, DL, MVT::i32, CCReg);
 185   SDValue SHL = DAG.getNode(ISD::SHL, DL, MVT::i32, IPM,
 186                             DAG.getConstant(30 - SystemZ::IPM_CC, DL, MVT::i32));
 187   SDValue SRA = DAG.getNode(ISD::SRA, DL, MVT::i32, SHL,
 188                             DAG.getConstant(30, DL, MVT::i32));
 189   return SRA;
 190 }
 191
 192 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemcmp(
 193     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
 194     SDValue Src2, SDValue Size, MachinePointerInfo Op1PtrInfo,
 195     MachinePointerInfo Op2PtrInfo) const {
 196   if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
 197     uint64_t Bytes = CSize->getZExtValue();
 198     assert(Bytes > 0 && "Caller should have handled 0-size case");
 199     // Swap operands to invert CC == 1 vs. CC == 2 cases.
 200     SDValue CCReg = emitCLC(DAG, DL, Chain, Src2, Src1, Bytes);
 201     Chain = CCReg.getValue(1);
 202     return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
 203   }
 204   return std::make_pair(SDValue(), SDValue());
 205 }
 206
 207 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemchr(
 208     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
 209     SDValue Char, SDValue Length, MachinePointerInfo SrcPtrInfo) const {
 210   // Use SRST to find the character.  End is its address on success.
 211   EVT PtrVT = Src.getValueType();
 212   SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
 213   Length = DAG.getZExtOrTrunc(Length, DL, PtrVT);
 214   Char = DAG.getZExtOrTrunc(Char, DL, MVT::i32);
 215   Char = DAG.getNode(ISD::AND, DL, MVT::i32, Char,
 216                      DAG.getConstant(255, DL, MVT::i32));
 217   SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, Length);
 218   SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
 219                             Limit, Src, Char);
 220   SDValue CCReg = End.getValue(1);
 221   Chain = End.getValue(2);
 222
 223   // Now select between End and null, depending on whether the character
 224   // was found.
 225   SDValue Ops[] = {
 226       End, DAG.getConstant(0, DL, PtrVT),
 227       DAG.getTargetConstant(SystemZ::CCMASK_SRST, DL, MVT::i32),
 228       DAG.getTargetConstant(SystemZ::CCMASK_SRST_FOUND, DL, MVT::i32), CCReg};
 229   End = DAG.getNode(SystemZISD::SELECT_CCMASK, DL, PtrVT, Ops);
 230   return std::make_pair(End, Chain);
 231 }
 232
 233 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcpy(
 234     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dest,
 235     SDValue Src, MachinePointerInfo DestPtrInfo, MachinePointerInfo SrcPtrInfo,
 236     bool isStpcpy) const {
 237   SDVTList VTs = DAG.getVTList(Dest.getValueType(), MVT::Other);
 238   SDValue EndDest = DAG.getNode(SystemZISD::STPCPY, DL, VTs, Chain, Dest, Src,
 239                                 DAG.getConstant(0, DL, MVT::i32));
 240   return std::make_pair(isStpcpy ? EndDest : Dest, EndDest.getValue(1));
 241 }
 242
 243 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcmp(
 244     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
 245     SDValue Src2, MachinePointerInfo Op1PtrInfo,
 246     MachinePointerInfo Op2PtrInfo) const {
 247   SDVTList VTs = DAG.getVTList(Src1.getValueType(), MVT::i32, MVT::Other);
 248   // Swap operands to invert CC == 1 vs. CC == 2 cases.
 249   SDValue Unused = DAG.getNode(SystemZISD::STRCMP, DL, VTs, Chain, Src2, Src1,
 250                                DAG.getConstant(0, DL, MVT::i32));
 251   SDValue CCReg = Unused.getValue(1);
 252   Chain = Unused.getValue(2);
 253   return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
 254 }
 255
 256 // Search from Src for a null character, stopping once Src reaches Limit.
 257 // Return a pair of values, the first being the number of nonnull characters
 258 // and the second being the out chain.
 259 //
 260 // This can be used for strlen by setting Limit to 0.
 261 static std::pair<SDValue, SDValue> getBoundedStrlen(SelectionDAG &DAG,
 262                                                     const SDLoc &DL,
 263                                                     SDValue Chain, SDValue Src,
 264                                                     SDValue Limit) {
 265   EVT PtrVT = Src.getValueType();
 266   SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
 267   SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
 268                             Limit, Src, DAG.getConstant(0, DL, MVT::i32));
 269   Chain = End.getValue(2);
 270   SDValue Len = DAG.getNode(ISD::SUB, DL, PtrVT, End, Src);
 271   return std::make_pair(Len, Chain);
 272 }
 273
 274 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrlen(
 275     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
 276     MachinePointerInfo SrcPtrInfo) const {
 277   EVT PtrVT = Src.getValueType();
 278   return getBoundedStrlen(DAG, DL, Chain, Src, DAG.getConstant(0, DL, PtrVT));
 279 }
 280
 281 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrnlen(
 282     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
 283     SDValue MaxLength, MachinePointerInfo SrcPtrInfo) const {
 284   EVT PtrVT = Src.getValueType();
 285   MaxLength = DAG.getZExtOrTrunc(MaxLength, DL, PtrVT);
 286   SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, MaxLength);
 287   return getBoundedStrlen(DAG, DL, Chain, Src, Limit);
 288 }