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, unsigned Align, 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, unsigned Align, bool IsVolatile,
78     MachinePointerInfo DstPtrInfo) const {
79   EVT PtrVT = Dst.getValueType();
80 
81   if (IsVolatile)
82     return SDValue();
83 
84   if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
85     uint64_t Bytes = CSize->getZExtValue();
86     if (Bytes == 0)
87       return SDValue();
88     if (auto *CByte = dyn_cast<ConstantSDNode>(Byte)) {
89       // Handle cases that can be done using at most two of
90       // MVI, MVHI, MVHHI and MVGHI.  The latter two can only be
91       // used if ByteVal is all zeros or all ones; in other casees,
92       // we can move at most 2 halfwords.
93       uint64_t ByteVal = CByte->getZExtValue();
94       if (ByteVal == 0 || ByteVal == 255 ?
95           Bytes <= 16 && countPopulation(Bytes) <= 2 :
96           Bytes <= 4) {
97         unsigned Size1 = Bytes == 16 ? 8 : 1 << findLastSet(Bytes);
98         unsigned Size2 = Bytes - Size1;
99         SDValue Chain1 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size1,
100                                      Align, DstPtrInfo);
101         if (Size2 == 0)
102           return Chain1;
103         Dst = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
104                           DAG.getConstant(Size1, DL, PtrVT));
105         DstPtrInfo = DstPtrInfo.getWithOffset(Size1);
106         SDValue Chain2 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size2,
107                                      std::min(Align, Size1), DstPtrInfo);
108         return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
109       }
110     } else {
111       // Handle one and two bytes using STC.
112       if (Bytes <= 2) {
113         SDValue Chain1 = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Align);
114         if (Bytes == 1)
115           return Chain1;
116         SDValue Dst2 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
117                                    DAG.getConstant(1, DL, PtrVT));
118         SDValue Chain2 =
119             DAG.getStore(Chain, DL, Byte, Dst2, DstPtrInfo.getWithOffset(1),
120                          /* Alignment = */ 1);
121         return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
122       }
123     }
124     assert(Bytes >= 2 && "Should have dealt with 0- and 1-byte cases already");
125 
126     // Handle the special case of a memset of 0, which can use XC.
127     auto *CByte = dyn_cast<ConstantSDNode>(Byte);
128     if (CByte && CByte->getZExtValue() == 0)
129       return emitMemMem(DAG, DL, SystemZISD::XC, SystemZISD::XC_LOOP,
130                         Chain, Dst, Dst, Bytes);
131 
132     // Copy the byte to the first location and then use MVC to copy
133     // it to the rest.
134     Chain = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Align);
135     SDValue DstPlus1 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
136                                    DAG.getConstant(1, DL, PtrVT));
137     return emitMemMem(DAG, DL, SystemZISD::MVC, SystemZISD::MVC_LOOP,
138                       Chain, DstPlus1, Dst, Bytes - 1);
139   }
140   return SDValue();
141 }
142 
143 // Use CLC to compare [Src1, Src1 + Size) with [Src2, Src2 + Size),
144 // deciding whether to use a loop or straight-line code.
145 static SDValue emitCLC(SelectionDAG &DAG, const SDLoc &DL, SDValue Chain,
146                        SDValue Src1, SDValue Src2, uint64_t Size) {
147   SDVTList VTs = DAG.getVTList(MVT::i32, MVT::Other);
148   EVT PtrVT = Src1.getValueType();
149   // A two-CLC sequence is a clear win over a loop, not least because it
150   // needs only one branch.  A three-CLC sequence needs the same number
151   // of branches as a loop (i.e. 2), but is shorter.  That brings us to
152   // lengths greater than 768 bytes.  It seems relatively likely that
153   // a difference will be found within the first 768 bytes, so we just
154   // optimize for the smallest number of branch instructions, in order
155   // to avoid polluting the prediction buffer too much.  A loop only ever
156   // needs 2 branches, whereas a straight-line sequence would need 3 or more.
157   if (Size > 3 * 256)
158     return DAG.getNode(SystemZISD::CLC_LOOP, DL, VTs, Chain, Src1, Src2,
159                        DAG.getConstant(Size, DL, PtrVT),
160                        DAG.getConstant(Size / 256, DL, PtrVT));
161   return DAG.getNode(SystemZISD::CLC, DL, VTs, Chain, Src1, Src2,
162                      DAG.getConstant(Size, DL, PtrVT));
163 }
164 
165 // Convert the current CC value into an integer that is 0 if CC == 0,
166 // less than zero if CC == 1 and greater than zero if CC >= 2.
167 // The sequence starts with IPM, which puts CC into bits 29 and 28
168 // of an integer and clears bits 30 and 31.
169 static SDValue addIPMSequence(const SDLoc &DL, SDValue CCReg,
170                               SelectionDAG &DAG) {
171   SDValue IPM = DAG.getNode(SystemZISD::IPM, DL, MVT::i32, CCReg);
172   SDValue SRL = DAG.getNode(ISD::SRL, DL, MVT::i32, IPM,
173                             DAG.getConstant(SystemZ::IPM_CC, DL, MVT::i32));
174   SDValue ROTL = DAG.getNode(ISD::ROTL, DL, MVT::i32, SRL,
175                              DAG.getConstant(31, DL, MVT::i32));
176   return ROTL;
177 }
178 
179 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemcmp(
180     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
181     SDValue Src2, SDValue Size, MachinePointerInfo Op1PtrInfo,
182     MachinePointerInfo Op2PtrInfo) const {
183   if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
184     uint64_t Bytes = CSize->getZExtValue();
185     assert(Bytes > 0 && "Caller should have handled 0-size case");
186     SDValue CCReg = emitCLC(DAG, DL, Chain, Src1, Src2, Bytes);
187     Chain = CCReg.getValue(1);
188     return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
189   }
190   return std::make_pair(SDValue(), SDValue());
191 }
192 
193 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemchr(
194     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
195     SDValue Char, SDValue Length, MachinePointerInfo SrcPtrInfo) const {
196   // Use SRST to find the character.  End is its address on success.
197   EVT PtrVT = Src.getValueType();
198   SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
199   Length = DAG.getZExtOrTrunc(Length, DL, PtrVT);
200   Char = DAG.getZExtOrTrunc(Char, DL, MVT::i32);
201   Char = DAG.getNode(ISD::AND, DL, MVT::i32, Char,
202                      DAG.getConstant(255, DL, MVT::i32));
203   SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, Length);
204   SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
205                             Limit, Src, Char);
206   SDValue CCReg = End.getValue(1);
207   Chain = End.getValue(2);
208 
209   // Now select between End and null, depending on whether the character
210   // was found.
211   SDValue Ops[] = {End, DAG.getConstant(0, DL, PtrVT),
212                    DAG.getConstant(SystemZ::CCMASK_SRST, DL, MVT::i32),
213                    DAG.getConstant(SystemZ::CCMASK_SRST_FOUND, DL, MVT::i32),
214                    CCReg};
215   End = DAG.getNode(SystemZISD::SELECT_CCMASK, DL, PtrVT, Ops);
216   return std::make_pair(End, Chain);
217 }
218 
219 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcpy(
220     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dest,
221     SDValue Src, MachinePointerInfo DestPtrInfo, MachinePointerInfo SrcPtrInfo,
222     bool isStpcpy) const {
223   SDVTList VTs = DAG.getVTList(Dest.getValueType(), MVT::Other);
224   SDValue EndDest = DAG.getNode(SystemZISD::STPCPY, DL, VTs, Chain, Dest, Src,
225                                 DAG.getConstant(0, DL, MVT::i32));
226   return std::make_pair(isStpcpy ? EndDest : Dest, EndDest.getValue(1));
227 }
228 
229 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcmp(
230     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
231     SDValue Src2, MachinePointerInfo Op1PtrInfo,
232     MachinePointerInfo Op2PtrInfo) const {
233   SDVTList VTs = DAG.getVTList(Src1.getValueType(), MVT::i32, MVT::Other);
234   SDValue Unused = DAG.getNode(SystemZISD::STRCMP, DL, VTs, Chain, Src1, Src2,
235                                DAG.getConstant(0, DL, MVT::i32));
236   SDValue CCReg = Unused.getValue(1);
237   Chain = Unused.getValue(2);
238   return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
239 }
240 
241 // Search from Src for a null character, stopping once Src reaches Limit.
242 // Return a pair of values, the first being the number of nonnull characters
243 // and the second being the out chain.
244 //
245 // This can be used for strlen by setting Limit to 0.
246 static std::pair<SDValue, SDValue> getBoundedStrlen(SelectionDAG &DAG,
247                                                     const SDLoc &DL,
248                                                     SDValue Chain, SDValue Src,
249                                                     SDValue Limit) {
250   EVT PtrVT = Src.getValueType();
251   SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
252   SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
253                             Limit, Src, DAG.getConstant(0, DL, MVT::i32));
254   Chain = End.getValue(2);
255   SDValue Len = DAG.getNode(ISD::SUB, DL, PtrVT, End, Src);
256   return std::make_pair(Len, Chain);
257 }
258 
259 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrlen(
260     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
261     MachinePointerInfo SrcPtrInfo) const {
262   EVT PtrVT = Src.getValueType();
263   return getBoundedStrlen(DAG, DL, Chain, Src, DAG.getConstant(0, DL, PtrVT));
264 }
265 
266 std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrnlen(
267     SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
268     SDValue MaxLength, MachinePointerInfo SrcPtrInfo) const {
269   EVT PtrVT = Src.getValueType();
270   MaxLength = DAG.getZExtOrTrunc(MaxLength, DL, PtrVT);
271   SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, MaxLength);
272   return getBoundedStrlen(DAG, DL, Chain, Src, Limit);
273 }
274