1 //===-- llvm/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "DbgValueHistoryCalculator.h"
11 #include "llvm/ADT/BitVector.h"
12 #include "llvm/ADT/SmallVector.h"
13 #include "llvm/CodeGen/MachineBasicBlock.h"
14 #include "llvm/CodeGen/MachineFunction.h"
15 #include "llvm/IR/DebugInfo.h"
16 #include "llvm/Support/Debug.h"
17 #include "llvm/Support/raw_ostream.h"
18 #include "llvm/Target/TargetRegisterInfo.h"
23 #define DEBUG_TYPE "dwarfdebug"
25 // \brief If @MI is a DBG_VALUE with debug value described by a
26 // defined register, returns the number of this register.
27 // In the other case, returns 0.
28 static unsigned isDescribedByReg(const MachineInstr &MI) {
29 assert(MI.isDebugValue());
30 assert(MI.getNumOperands() == 4);
31 // If location of variable is described using a register (directly or
32 // indirecltly), this register is always a first operand.
33 return MI.getOperand(0).isReg() ? MI.getOperand(0).getReg() : 0;
36 void DbgValueHistoryMap::startInstrRange(InlinedVariable Var,
37 const MachineInstr &MI) {
38 // Instruction range should start with a DBG_VALUE instruction for the
40 assert(MI.isDebugValue() && "not a DBG_VALUE");
41 auto &Ranges = VarInstrRanges[Var];
42 if (!Ranges.empty() && Ranges.back().second == nullptr &&
43 Ranges.back().first->isIdenticalTo(&MI)) {
44 DEBUG(dbgs() << "Coalescing identical DBG_VALUE entries:\n"
45 << "\t" << Ranges.back().first << "\t" << MI << "\n");
48 Ranges.push_back(std::make_pair(&MI, nullptr));
51 void DbgValueHistoryMap::endInstrRange(InlinedVariable Var,
52 const MachineInstr &MI) {
53 auto &Ranges = VarInstrRanges[Var];
54 // Verify that the current instruction range is not yet closed.
55 assert(!Ranges.empty() && Ranges.back().second == nullptr);
56 // For now, instruction ranges are not allowed to cross basic block
58 assert(Ranges.back().first->getParent() == MI.getParent());
59 Ranges.back().second = &MI;
62 unsigned DbgValueHistoryMap::getRegisterForVar(InlinedVariable Var) const {
63 const auto &I = VarInstrRanges.find(Var);
64 if (I == VarInstrRanges.end())
66 const auto &Ranges = I->second;
67 if (Ranges.empty() || Ranges.back().second != nullptr)
69 return isDescribedByReg(*Ranges.back().first);
73 // Maps physreg numbers to the variables they describe.
74 typedef DbgValueHistoryMap::InlinedVariable InlinedVariable;
75 typedef std::map<unsigned, SmallVector<InlinedVariable, 1>> RegDescribedVarsMap;
78 // \brief Claim that @Var is not described by @RegNo anymore.
79 static void dropRegDescribedVar(RegDescribedVarsMap &RegVars, unsigned RegNo,
80 InlinedVariable Var) {
81 const auto &I = RegVars.find(RegNo);
82 assert(RegNo != 0U && I != RegVars.end());
83 auto &VarSet = I->second;
84 const auto &VarPos = std::find(VarSet.begin(), VarSet.end(), Var);
85 assert(VarPos != VarSet.end());
87 // Don't keep empty sets in a map to keep it as small as possible.
92 // \brief Claim that @Var is now described by @RegNo.
93 static void addRegDescribedVar(RegDescribedVarsMap &RegVars, unsigned RegNo,
94 InlinedVariable Var) {
96 auto &VarSet = RegVars[RegNo];
97 assert(std::find(VarSet.begin(), VarSet.end(), Var) == VarSet.end());
98 VarSet.push_back(Var);
101 // \brief Terminate the location range for variables described by register at
102 // @I by inserting @ClobberingInstr to their history.
103 static void clobberRegisterUses(RegDescribedVarsMap &RegVars,
104 RegDescribedVarsMap::iterator I,
105 DbgValueHistoryMap &HistMap,
106 const MachineInstr &ClobberingInstr) {
107 // Iterate over all variables described by this register and add this
108 // instruction to their history, clobbering it.
109 for (const auto &Var : I->second)
110 HistMap.endInstrRange(Var, ClobberingInstr);
114 // \brief Terminate the location range for variables described by register
115 // @RegNo by inserting @ClobberingInstr to their history.
116 static void clobberRegisterUses(RegDescribedVarsMap &RegVars, unsigned RegNo,
117 DbgValueHistoryMap &HistMap,
118 const MachineInstr &ClobberingInstr) {
119 const auto &I = RegVars.find(RegNo);
120 if (I == RegVars.end())
122 clobberRegisterUses(RegVars, I, HistMap, ClobberingInstr);
125 // \brief Collect all registers clobbered by @MI and apply the functor
126 // @Func to their RegNo.
127 // @Func should be a functor with a void(unsigned) signature. We're
128 // not using std::function here for performance reasons. It has a
129 // small but measurable impact. By using a functor instead of a
130 // std::set& here, we can avoid the overhead of constructing
131 // temporaries in calculateDbgValueHistory, which has a significant
132 // performance impact.
133 template<typename Callable>
134 static void applyToClobberedRegisters(const MachineInstr &MI,
135 const TargetRegisterInfo *TRI,
137 for (const MachineOperand &MO : MI.operands()) {
138 if (!MO.isReg() || !MO.isDef() || !MO.getReg())
140 for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI)
145 // \brief Returns the first instruction in @MBB which corresponds to
146 // the function epilogue, or nullptr if @MBB doesn't contain an epilogue.
147 static const MachineInstr *getFirstEpilogueInst(const MachineBasicBlock &MBB) {
148 auto LastMI = MBB.getLastNonDebugInstr();
149 if (LastMI == MBB.end() || !LastMI->isReturn())
151 // Assume that epilogue starts with instruction having the same debug location
152 // as the return instruction.
153 DebugLoc LastLoc = LastMI->getDebugLoc();
155 for (MachineBasicBlock::const_reverse_iterator I(std::next(LastMI)),
158 if (I->getDebugLoc() != LastLoc)
162 // If all instructions have the same debug location, assume whole MBB is
167 // \brief Collect registers that are modified in the function body (their
168 // contents is changed outside of the prologue and epilogue).
169 static void collectChangingRegs(const MachineFunction *MF,
170 const TargetRegisterInfo *TRI,
172 for (const auto &MBB : *MF) {
173 auto FirstEpilogueInst = getFirstEpilogueInst(MBB);
175 for (const auto &MI : MBB) {
176 if (&MI == FirstEpilogueInst)
178 if (!MI.getFlag(MachineInstr::FrameSetup))
179 applyToClobberedRegisters(MI, TRI, [&](unsigned r) { Regs.set(r); });
184 void llvm::calculateDbgValueHistory(const MachineFunction *MF,
185 const TargetRegisterInfo *TRI,
186 DbgValueHistoryMap &Result) {
187 BitVector ChangingRegs(TRI->getNumRegs());
188 collectChangingRegs(MF, TRI, ChangingRegs);
190 RegDescribedVarsMap RegVars;
191 for (const auto &MBB : *MF) {
192 for (const auto &MI : MBB) {
193 if (!MI.isDebugValue()) {
194 // Not a DBG_VALUE instruction. It may clobber registers which describe
196 applyToClobberedRegisters(MI, TRI, [&](unsigned RegNo) {
197 if (ChangingRegs.test(RegNo))
198 clobberRegisterUses(RegVars, RegNo, Result, MI);
203 assert(MI.getNumOperands() > 1 && "Invalid DBG_VALUE instruction!");
204 // Use the base variable (without any DW_OP_piece expressions)
205 // as index into History. The full variables including the
206 // piece expressions are attached to the MI.
207 const DILocalVariable *RawVar = MI.getDebugVariable();
208 assert(RawVar->isValidLocationForIntrinsic(MI.getDebugLoc()) &&
209 "Expected inlined-at fields to agree");
210 InlinedVariable Var(RawVar, MI.getDebugLoc()->getInlinedAt());
212 if (unsigned PrevReg = Result.getRegisterForVar(Var))
213 dropRegDescribedVar(RegVars, PrevReg, Var);
215 Result.startInstrRange(Var, MI);
217 if (unsigned NewReg = isDescribedByReg(MI))
218 addRegDescribedVar(RegVars, NewReg, Var);
221 // Make sure locations for register-described variables are valid only
222 // until the end of the basic block (unless it's the last basic block, in
223 // which case let their liveness run off to the end of the function).
224 if (!MBB.empty() && &MBB != &MF->back()) {
225 for (auto I = RegVars.begin(), E = RegVars.end(); I != E;) {
226 auto CurElem = I++; // CurElem can be erased below.
227 if (ChangingRegs.test(CurElem->first))
228 clobberRegisterUses(RegVars, CurElem, Result, MBB.back());