Bug Summary

File:lib/Target/AVR/AVRRegisterInfo.cpp
Warning:line 235, column 5
Value stored to 'New' is never read

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name AVRRegisterInfo.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-8/lib/clang/8.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/lib/Target/AVR -I /build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/include -I /build/llvm-toolchain-snapshot-8~svn345461/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/include/clang/8.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-8/lib/clang/8.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/lib/Target/AVR -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-10-27-211344-32123-1 -x c++ /build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp -faddrsig
1//===-- AVRRegisterInfo.cpp - AVR Register Information --------------------===//
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 contains the AVR implementation of the TargetRegisterInfo class.
11//
12//===----------------------------------------------------------------------===//
13
14#include "AVRRegisterInfo.h"
15
16#include "llvm/ADT/BitVector.h"
17#include "llvm/CodeGen/MachineFrameInfo.h"
18#include "llvm/CodeGen/MachineFunction.h"
19#include "llvm/CodeGen/MachineInstrBuilder.h"
20#include "llvm/IR/Function.h"
21#include "llvm/CodeGen/TargetFrameLowering.h"
22
23#include "AVR.h"
24#include "AVRInstrInfo.h"
25#include "AVRTargetMachine.h"
26#include "MCTargetDesc/AVRMCTargetDesc.h"
27
28#define GET_REGINFO_TARGET_DESC
29#include "AVRGenRegisterInfo.inc"
30
31namespace llvm {
32
33AVRRegisterInfo::AVRRegisterInfo() : AVRGenRegisterInfo(0) {}
34
35const uint16_t *
36AVRRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
37 CallingConv::ID CC = MF->getFunction().getCallingConv();
38
39 return ((CC == CallingConv::AVR_INTR || CC == CallingConv::AVR_SIGNAL)
40 ? CSR_Interrupts_SaveList
41 : CSR_Normal_SaveList);
42}
43
44const uint32_t *
45AVRRegisterInfo::getCallPreservedMask(const MachineFunction &MF,
46 CallingConv::ID CC) const {
47 return ((CC == CallingConv::AVR_INTR || CC == CallingConv::AVR_SIGNAL)
48 ? CSR_Interrupts_RegMask
49 : CSR_Normal_RegMask);
50}
51
52BitVector AVRRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
53 BitVector Reserved(getNumRegs());
54
55 // Reserve the intermediate result registers r1 and r2
56 // The result of instructions like 'mul' is always stored here.
57 Reserved.set(AVR::R0);
58 Reserved.set(AVR::R1);
59 Reserved.set(AVR::R1R0);
60
61 // Reserve the stack pointer.
62 Reserved.set(AVR::SPL);
63 Reserved.set(AVR::SPH);
64 Reserved.set(AVR::SP);
65
66 // We tenatively reserve the frame pointer register r29:r28 because the
67 // function may require one, but we cannot tell until register allocation
68 // is complete, which can be too late.
69 //
70 // Instead we just unconditionally reserve the Y register.
71 //
72 // TODO: Write a pass to enumerate functions which reserved the Y register
73 // but didn't end up needing a frame pointer. In these, we can
74 // convert one or two of the spills inside to use the Y register.
75 Reserved.set(AVR::R28);
76 Reserved.set(AVR::R29);
77 Reserved.set(AVR::R29R28);
78
79 return Reserved;
80}
81
82const TargetRegisterClass *
83AVRRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC,
84 const MachineFunction &MF) const {
85 const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
86 if (TRI->isTypeLegalForClass(*RC, MVT::i16)) {
87 return &AVR::DREGSRegClass;
88 }
89
90 if (TRI->isTypeLegalForClass(*RC, MVT::i8)) {
91 return &AVR::GPR8RegClass;
92 }
93
94 llvm_unreachable("Invalid register size")::llvm::llvm_unreachable_internal("Invalid register size", "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 94);
95}
96
97/// Fold a frame offset shared between two add instructions into a single one.
98static void foldFrameOffset(MachineBasicBlock::iterator &II, int &Offset, unsigned DstReg) {
99 MachineInstr &MI = *II;
100 int Opcode = MI.getOpcode();
101
102 // Don't bother trying if the next instruction is not an add or a sub.
103 if ((Opcode != AVR::SUBIWRdK) && (Opcode != AVR::ADIWRdK)) {
104 return;
105 }
106
107 // Check that DstReg matches with next instruction, otherwise the instruction
108 // is not related to stack address manipulation.
109 if (DstReg != MI.getOperand(0).getReg()) {
110 return;
111 }
112
113 // Add the offset in the next instruction to our offset.
114 switch (Opcode) {
115 case AVR::SUBIWRdK:
116 Offset += -MI.getOperand(2).getImm();
117 break;
118 case AVR::ADIWRdK:
119 Offset += MI.getOperand(2).getImm();
120 break;
121 }
122
123 // Finally remove the instruction.
124 II++;
125 MI.eraseFromParent();
126}
127
128void AVRRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
129 int SPAdj, unsigned FIOperandNum,
130 RegScavenger *RS) const {
131 assert(SPAdj == 0 && "Unexpected SPAdj value")((SPAdj == 0 && "Unexpected SPAdj value") ? static_cast
<void> (0) : __assert_fail ("SPAdj == 0 && \"Unexpected SPAdj value\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 131, __PRETTY_FUNCTION__));
132
133 MachineInstr &MI = *II;
134 DebugLoc dl = MI.getDebugLoc();
135 MachineBasicBlock &MBB = *MI.getParent();
136 const MachineFunction &MF = *MBB.getParent();
137 const AVRTargetMachine &TM = (const AVRTargetMachine &)MF.getTarget();
138 const TargetInstrInfo &TII = *TM.getSubtargetImpl()->getInstrInfo();
139 const MachineFrameInfo &MFI = MF.getFrameInfo();
140 const TargetFrameLowering *TFI = TM.getSubtargetImpl()->getFrameLowering();
141 int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
142 int Offset = MFI.getObjectOffset(FrameIndex);
143
144 // Add one to the offset because SP points to an empty slot.
145 Offset += MFI.getStackSize() - TFI->getOffsetOfLocalArea() + 1;
146 // Fold incoming offset.
147 Offset += MI.getOperand(FIOperandNum + 1).getImm();
148
149 // This is actually "load effective address" of the stack slot
150 // instruction. We have only two-address instructions, thus we need to
151 // expand it into move + add.
152 if (MI.getOpcode() == AVR::FRMIDX) {
153 MI.setDesc(TII.get(AVR::MOVWRdRr));
154 MI.getOperand(FIOperandNum).ChangeToRegister(AVR::R29R28, false);
155
156 assert(Offset > 0 && "Invalid offset")((Offset > 0 && "Invalid offset") ? static_cast<
void> (0) : __assert_fail ("Offset > 0 && \"Invalid offset\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 156, __PRETTY_FUNCTION__));
157
158 // We need to materialize the offset via an add instruction.
159 unsigned Opcode;
160 unsigned DstReg = MI.getOperand(0).getReg();
161 assert(DstReg != AVR::R29R28 && "Dest reg cannot be the frame pointer")((DstReg != AVR::R29R28 && "Dest reg cannot be the frame pointer"
) ? static_cast<void> (0) : __assert_fail ("DstReg != AVR::R29R28 && \"Dest reg cannot be the frame pointer\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 161, __PRETTY_FUNCTION__));
162
163 II++; // Skip over the FRMIDX (and now MOVW) instruction.
164
165 // Generally, to load a frame address two add instructions are emitted that
166 // could get folded into a single one:
167 // movw r31:r30, r29:r28
168 // adiw r31:r30, 29
169 // adiw r31:r30, 16
170 // to:
171 // movw r31:r30, r29:r28
172 // adiw r31:r30, 45
173 if (II != MBB.end())
174 foldFrameOffset(II, Offset, DstReg);
175
176 // Select the best opcode based on DstReg and the offset size.
177 switch (DstReg) {
178 case AVR::R25R24:
179 case AVR::R27R26:
180 case AVR::R31R30: {
181 if (isUInt<6>(Offset)) {
182 Opcode = AVR::ADIWRdK;
183 break;
184 }
185 LLVM_FALLTHROUGH[[clang::fallthrough]];
186 }
187 default: {
188 // This opcode will get expanded into a pair of subi/sbci.
189 Opcode = AVR::SUBIWRdK;
190 Offset = -Offset;
191 break;
192 }
193 }
194
195 MachineInstr *New = BuildMI(MBB, II, dl, TII.get(Opcode), DstReg)
196 .addReg(DstReg, RegState::Kill)
197 .addImm(Offset);
198 New->getOperand(3).setIsDead();
199
200 return;
201 }
202
203 // If the offset is too big we have to adjust and restore the frame pointer
204 // to materialize a valid load/store with displacement.
205 //:TODO: consider using only one adiw/sbiw chain for more than one frame index
206 if (Offset > 62) {
207 unsigned AddOpc = AVR::ADIWRdK, SubOpc = AVR::SBIWRdK;
208 int AddOffset = Offset - 63 + 1;
209
210 // For huge offsets where adiw/sbiw cannot be used use a pair of subi/sbci.
211 if ((Offset - 63 + 1) > 63) {
212 AddOpc = AVR::SUBIWRdK;
213 SubOpc = AVR::SUBIWRdK;
214 AddOffset = -AddOffset;
215 }
216
217 // It is possible that the spiller places this frame instruction in between
218 // a compare and branch, invalidating the contents of SREG set by the
219 // compare instruction because of the add/sub pairs. Conservatively save and
220 // restore SREG before and after each add/sub pair.
221 BuildMI(MBB, II, dl, TII.get(AVR::INRdA), AVR::R0).addImm(0x3f);
222
223 MachineInstr *New = BuildMI(MBB, II, dl, TII.get(AddOpc), AVR::R29R28)
224 .addReg(AVR::R29R28, RegState::Kill)
225 .addImm(AddOffset);
226 New->getOperand(3).setIsDead();
227
228 // Restore SREG.
229 BuildMI(MBB, std::next(II), dl, TII.get(AVR::OUTARr))
230 .addImm(0x3f)
231 .addReg(AVR::R0, RegState::Kill);
232
233 // No need to set SREG as dead here otherwise if the next instruction is a
234 // cond branch it will be using a dead register.
235 New = BuildMI(MBB, std::next(II), dl, TII.get(SubOpc), AVR::R29R28)
Value stored to 'New' is never read
236 .addReg(AVR::R29R28, RegState::Kill)
237 .addImm(Offset - 63 + 1);
238
239 Offset = 62;
240 }
241
242 MI.getOperand(FIOperandNum).ChangeToRegister(AVR::R29R28, false);
243 assert(isUInt<6>(Offset) && "Offset is out of range")((isUInt<6>(Offset) && "Offset is out of range"
) ? static_cast<void> (0) : __assert_fail ("isUInt<6>(Offset) && \"Offset is out of range\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 243, __PRETTY_FUNCTION__));
244 MI.getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
245}
246
247unsigned AVRRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
248 const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
249 if (TFI->hasFP(MF)) {
250 // The Y pointer register
251 return AVR::R28;
252 }
253
254 return AVR::SP;
255}
256
257const TargetRegisterClass *
258AVRRegisterInfo::getPointerRegClass(const MachineFunction &MF,
259 unsigned Kind) const {
260 // FIXME: Currently we're using avr-gcc as reference, so we restrict
261 // ptrs to Y and Z regs. Though avr-gcc has buggy implementation
262 // of memory constraint, so we can fix it and bit avr-gcc here ;-)
263 return &AVR::PTRDISPREGSRegClass;
264}
265
266void AVRRegisterInfo::splitReg(unsigned Reg,
267 unsigned &LoReg,
268 unsigned &HiReg) const {
269 assert(AVR::DREGSRegClass.contains(Reg) && "can only split 16-bit registers")((AVR::DREGSRegClass.contains(Reg) && "can only split 16-bit registers"
) ? static_cast<void> (0) : __assert_fail ("AVR::DREGSRegClass.contains(Reg) && \"can only split 16-bit registers\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/Target/AVR/AVRRegisterInfo.cpp"
, 269, __PRETTY_FUNCTION__));
270
271 LoReg = getSubReg(Reg, AVR::sub_lo);
272 HiReg = getSubReg(Reg, AVR::sub_hi);
273}
274
275} // end of namespace llvm