Bug Summary

File:llvm/lib/Target/X86/X86LowerTileCopy.cpp
Warning:line 119, column 7
Value stored to 'NewMI' is never read

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name X86LowerTileCopy.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 -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/build-llvm -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/Target/X86 -I /build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/llvm/lib/Target/X86 -I include -I /build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/llvm/include -D _FORTIFY_SOURCE=2 -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fmacro-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/= -O3 -Wno-unused-command-line-argument -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/= -ferror-limit 19 -fvisibility hidden -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2022-01-25-232935-20746-1 -x c++ /build/llvm-toolchain-snapshot-14~++20220125101009+ceec4383681c/llvm/lib/Target/X86/X86LowerTileCopy.cpp
1//===-- X86LowerTileCopy.cpp - Expand Tile Copy Instructions---------------===//
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 defines the pass which lower AMX tile copy instructions. Since
10// there is no tile copy instruction, we need store tile register to stack
11// and load from stack to another tile register. We need extra GR to hold
12// the stride, and we need stack slot to hold the tile data register.
13// We would run this pass after copy propagation, so that we don't miss copy
14// optimization. And we would run this pass before prolog/epilog insertion,
15// so that we can allocate stack slot.
16//
17//===----------------------------------------------------------------------===//
18
19#include "X86.h"
20#include "X86InstrBuilder.h"
21#include "X86InstrInfo.h"
22#include "X86Subtarget.h"
23#include "llvm/CodeGen/MachineBasicBlock.h"
24#include "llvm/CodeGen/MachineFrameInfo.h"
25#include "llvm/CodeGen/MachineFunction.h"
26#include "llvm/CodeGen/MachineFunctionPass.h"
27#include "llvm/CodeGen/MachineInstr.h"
28#include "llvm/CodeGen/MachineInstrBuilder.h"
29#include "llvm/CodeGen/MachineOperand.h"
30#include "llvm/CodeGen/Passes.h"
31#include "llvm/IR/DebugLoc.h"
32#include "llvm/InitializePasses.h"
33#include "llvm/Support/Debug.h"
34
35using namespace llvm;
36
37#define DEBUG_TYPE"x86-lower-tile-copy" "x86-lower-tile-copy"
38
39namespace {
40
41class X86LowerTileCopy : public MachineFunctionPass {
42public:
43 static char ID;
44
45 X86LowerTileCopy() : MachineFunctionPass(ID) {}
46
47 void getAnalysisUsage(AnalysisUsage &AU) const override;
48
49 bool runOnMachineFunction(MachineFunction &MF) override;
50
51 StringRef getPassName() const override { return "X86 Lower Tile Copy"; }
52};
53
54} // namespace
55
56char X86LowerTileCopy::ID = 0;
57
58INITIALIZE_PASS_BEGIN(X86LowerTileCopy, "lowertilecopy", "Tile Copy Lowering",static void *initializeX86LowerTileCopyPassOnce(PassRegistry &
Registry) {
59 false, false)static void *initializeX86LowerTileCopyPassOnce(PassRegistry &
Registry) {
60INITIALIZE_PASS_END(X86LowerTileCopy, "lowertilecopy", "Tile Copy Lowering",PassInfo *PI = new PassInfo( "Tile Copy Lowering", "lowertilecopy"
, &X86LowerTileCopy::ID, PassInfo::NormalCtor_t(callDefaultCtor
<X86LowerTileCopy>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeX86LowerTileCopyPassFlag
; void llvm::initializeX86LowerTileCopyPass(PassRegistry &
Registry) { llvm::call_once(InitializeX86LowerTileCopyPassFlag
, initializeX86LowerTileCopyPassOnce, std::ref(Registry)); }
61 false, false)PassInfo *PI = new PassInfo( "Tile Copy Lowering", "lowertilecopy"
, &X86LowerTileCopy::ID, PassInfo::NormalCtor_t(callDefaultCtor
<X86LowerTileCopy>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeX86LowerTileCopyPassFlag
; void llvm::initializeX86LowerTileCopyPass(PassRegistry &
Registry) { llvm::call_once(InitializeX86LowerTileCopyPassFlag
, initializeX86LowerTileCopyPassOnce, std::ref(Registry)); }
62
63void X86LowerTileCopy::getAnalysisUsage(AnalysisUsage &AU) const {
64 AU.setPreservesAll();
65 MachineFunctionPass::getAnalysisUsage(AU);
66}
67
68FunctionPass *llvm::createX86LowerTileCopyPass() {
69 return new X86LowerTileCopy();
70}
71
72bool X86LowerTileCopy::runOnMachineFunction(MachineFunction &MF) {
73 const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
74 const X86InstrInfo *TII = ST.getInstrInfo();
75 bool Changed = false;
76
77 for (MachineBasicBlock &MBB : MF) {
78 for (MachineInstr &MI : llvm::make_early_inc_range(MBB)) {
79 if (!MI.isCopy())
80 continue;
81 MachineOperand &DstMO = MI.getOperand(0);
82 MachineOperand &SrcMO = MI.getOperand(1);
83 Register SrcReg = SrcMO.getReg();
84 Register DstReg = DstMO.getReg();
85 if (!X86::TILERegClass.contains(DstReg, SrcReg))
86 continue;
87
88 const TargetRegisterInfo *TRI = ST.getRegisterInfo();
89 // Allocate stack slot for tile register
90 unsigned Size = TRI->getSpillSize(X86::TILERegClass);
91 Align Alignment = TRI->getSpillAlign(X86::TILERegClass);
92 int TileSS = MF.getFrameInfo().CreateSpillStackObject(Size, Alignment);
93 // Allocate stack slot for stride register
94 Size = TRI->getSpillSize(X86::GR64RegClass);
95 Alignment = TRI->getSpillAlign(X86::GR64RegClass);
96 int StrideSS = MF.getFrameInfo().CreateSpillStackObject(Size, Alignment);
97
98 // TODO: Pick a killed regiter to avoid save/reload. There is problem
99 // to get live interval in this stage.
100 Register GR64Cand = X86::RAX;
101
102 const DebugLoc &DL = MI.getDebugLoc();
103 // mov %rax (%sp)
104 BuildMI(MBB, MI, DL, TII->get(X86::IMPLICIT_DEF), GR64Cand);
105 addFrameReference(BuildMI(MBB, MI, DL, TII->get(X86::MOV64mr)), StrideSS)
106 .addReg(GR64Cand);
107 // mov 64 %rax
108 BuildMI(MBB, MI, DL, TII->get(X86::MOV64ri), GR64Cand).addImm(64);
109 // tilestored %tmm, (%sp, %idx)
110 unsigned Opc = X86::TILESTORED;
111 MachineInstr *NewMI =
112 addFrameReference(BuildMI(MBB, MI, DL, TII->get(Opc)), TileSS)
113 .addReg(SrcReg, getKillRegState(SrcMO.isKill()));
114 MachineOperand &MO = NewMI->getOperand(2);
115 MO.setReg(GR64Cand);
116 MO.setIsKill(true);
117 // tileloadd (%sp, %idx), %tmm
118 Opc = X86::TILELOADD;
119 NewMI = addFrameReference(BuildMI(MBB, MI, DL, TII->get(Opc), DstReg),
Value stored to 'NewMI' is never read
120 TileSS);
121 // restore %rax
122 // mov (%sp) %rax
123 addFrameReference(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm), GR64Cand),
124 StrideSS);
125 MI.eraseFromParent();
126 Changed = true;
127 }
128 }
129 return Changed;
130}