1//===-- llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp -------*- C++ -*--===//
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// Common functionality for different debug information format backends.
10// LLVM currently supports DWARF and CodeView.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/DebugHandlerBase.h"
15#include "llvm/CodeGen/AsmPrinter.h"
16#include "llvm/CodeGen/MachineFunction.h"
17#include "llvm/CodeGen/MachineInstr.h"
18#include "llvm/CodeGen/MachineModuleInfo.h"
19#include "llvm/CodeGen/TargetSubtargetInfo.h"
20#include "llvm/IR/DebugInfo.h"
21#include "llvm/MC/MCStreamer.h"
22#include "llvm/Support/CommandLine.h"
23
24using namespace llvm;
25
26#define DEBUG_TYPE "dwarfdebug"
27
28/// If true, we drop variable location ranges which exist entirely outside the
29/// variable's lexical scope instruction ranges.
30static cl::opt<bool> TrimVarLocs("trim-var-locs", cl::Hidden, cl::init(Val: true));
31
32std::optional<DbgVariableLocation>
33DbgVariableLocation::extractFromMachineInstruction(
34 const MachineInstr &Instruction) {
35 DbgVariableLocation Location;
36 // Variables calculated from multiple locations can't be represented here.
37 if (Instruction.getNumDebugOperands() != 1)
38 return std::nullopt;
39 if (!Instruction.getDebugOperand(Index: 0).isReg())
40 return std::nullopt;
41 Location.Register = Instruction.getDebugOperand(Index: 0).getReg();
42 Location.FragmentInfo.reset();
43 // We only handle expressions generated by DIExpression::appendOffset,
44 // which doesn't require a full stack machine.
45 int64_t Offset = 0;
46 const DIExpression *DIExpr = Instruction.getDebugExpression();
47 auto Op = DIExpr->expr_op_begin();
48 // We can handle a DBG_VALUE_LIST iff it has exactly one location operand that
49 // appears exactly once at the start of the expression.
50 if (Instruction.isDebugValueList()) {
51 if (Instruction.getNumDebugOperands() == 1 &&
52 Op->getOp() == dwarf::DW_OP_LLVM_arg)
53 ++Op;
54 else
55 return std::nullopt;
56 }
57 while (Op != DIExpr->expr_op_end()) {
58 switch (Op->getOp()) {
59 case dwarf::DW_OP_constu: {
60 int Value = Op->getArg(I: 0);
61 ++Op;
62 if (Op != DIExpr->expr_op_end()) {
63 switch (Op->getOp()) {
64 case dwarf::DW_OP_minus:
65 Offset -= Value;
66 break;
67 case dwarf::DW_OP_plus:
68 Offset += Value;
69 break;
70 default:
71 continue;
72 }
73 }
74 } break;
75 case dwarf::DW_OP_plus_uconst:
76 Offset += Op->getArg(I: 0);
77 break;
78 case dwarf::DW_OP_LLVM_fragment:
79 Location.FragmentInfo = {Op->getArg(I: 1), Op->getArg(I: 0)};
80 break;
81 case dwarf::DW_OP_deref:
82 Location.LoadChain.push_back(Elt: Offset);
83 Offset = 0;
84 break;
85 default:
86 return std::nullopt;
87 }
88 ++Op;
89 }
90
91 // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
92 // instruction.
93 // FIXME: Replace these with DIExpression.
94 if (Instruction.isIndirectDebugValue())
95 Location.LoadChain.push_back(Elt: Offset);
96
97 return Location;
98}
99
100DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
101
102void DebugHandlerBase::beginModule(Module *M) {
103 if (M->debug_compile_units().empty())
104 Asm = nullptr;
105}
106
107// Each LexicalScope has first instruction and last instruction to mark
108// beginning and end of a scope respectively. Create an inverse map that list
109// scopes starts (and ends) with an instruction. One instruction may start (or
110// end) multiple scopes. Ignore scopes that are not reachable.
111void DebugHandlerBase::identifyScopeMarkers() {
112 SmallVector<LexicalScope *, 4> WorkList;
113 WorkList.push_back(Elt: LScopes.getCurrentFunctionScope());
114 while (!WorkList.empty()) {
115 LexicalScope *S = WorkList.pop_back_val();
116
117 const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
118 if (!Children.empty())
119 WorkList.append(in_start: Children.begin(), in_end: Children.end());
120
121 if (S->isAbstractScope())
122 continue;
123
124 for (const InsnRange &R : S->getRanges()) {
125 assert(R.first && "InsnRange does not have first instruction!");
126 assert(R.second && "InsnRange does not have second instruction!");
127 requestLabelBeforeInsn(MI: R.first);
128 requestLabelAfterInsn(MI: R.second);
129 }
130 }
131}
132
133// Return Label preceding the instruction.
134MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
135 MCSymbol *Label = LabelsBeforeInsn.lookup(Val: MI);
136 assert(Label && "Didn't insert label before instruction");
137 return Label;
138}
139
140// Return Label immediately following the instruction.
141MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
142 return LabelsAfterInsn.lookup(Val: MI);
143}
144
145/// If this type is derived from a base type then return base type size.
146uint64_t DebugHandlerBase::getBaseTypeSize(const DIType *Ty) {
147 assert(Ty);
148 const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Val: Ty);
149 if (!DDTy)
150 return Ty->getSizeInBits();
151
152 unsigned Tag = DDTy->getTag();
153
154 if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
155 Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
156 Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type &&
157 Tag != dwarf::DW_TAG_immutable_type &&
158 Tag != dwarf::DW_TAG_template_alias)
159 return DDTy->getSizeInBits();
160
161 DIType *BaseType = DDTy->getBaseType();
162
163 if (!BaseType)
164 return 0;
165
166 // If this is a derived type, go ahead and get the base type, unless it's a
167 // reference then it's just the size of the field. Pointer types have no need
168 // of this since they're a different type of qualification on the type.
169 if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
170 BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
171 return Ty->getSizeInBits();
172
173 return getBaseTypeSize(Ty: BaseType);
174}
175
176bool DebugHandlerBase::isUnsignedDIType(const DIType *Ty) {
177 if (isa<DIStringType>(Val: Ty)) {
178 // Some transformations (e.g. instcombine) may decide to turn a Fortran
179 // character object into an integer, and later ones (e.g. SROA) may
180 // further inject a constant integer in a llvm.dbg.value call to track
181 // the object's value. Here we trust the transformations are doing the
182 // right thing, and treat the constant as unsigned to preserve that value
183 // (i.e. avoid sign extension).
184 return true;
185 }
186
187 if (auto *CTy = dyn_cast<DICompositeType>(Val: Ty)) {
188 if (CTy->getTag() == dwarf::DW_TAG_enumeration_type) {
189 if (!(Ty = CTy->getBaseType()))
190 // FIXME: Enums without a fixed underlying type have unknown signedness
191 // here, leading to incorrectly emitted constants.
192 return false;
193 } else
194 // (Pieces of) aggregate types that get hacked apart by SROA may be
195 // represented by a constant. Encode them as unsigned bytes.
196 return true;
197 }
198
199 if (auto *DTy = dyn_cast<DIDerivedType>(Val: Ty)) {
200 dwarf::Tag T = (dwarf::Tag)Ty->getTag();
201 // Encode pointer constants as unsigned bytes. This is used at least for
202 // null pointer constant emission.
203 // FIXME: reference and rvalue_reference /probably/ shouldn't be allowed
204 // here, but accept them for now due to a bug in SROA producing bogus
205 // dbg.values.
206 if (T == dwarf::DW_TAG_pointer_type ||
207 T == dwarf::DW_TAG_ptr_to_member_type ||
208 T == dwarf::DW_TAG_reference_type ||
209 T == dwarf::DW_TAG_rvalue_reference_type)
210 return true;
211 assert(T == dwarf::DW_TAG_typedef || T == dwarf::DW_TAG_const_type ||
212 T == dwarf::DW_TAG_volatile_type ||
213 T == dwarf::DW_TAG_restrict_type || T == dwarf::DW_TAG_atomic_type ||
214 T == dwarf::DW_TAG_immutable_type ||
215 T == dwarf::DW_TAG_template_alias);
216 assert(DTy->getBaseType() && "Expected valid base type");
217 return isUnsignedDIType(Ty: DTy->getBaseType());
218 }
219
220 auto *BTy = cast<DIBasicType>(Val: Ty);
221 unsigned Encoding = BTy->getEncoding();
222 assert((Encoding == dwarf::DW_ATE_unsigned ||
223 Encoding == dwarf::DW_ATE_unsigned_char ||
224 Encoding == dwarf::DW_ATE_signed ||
225 Encoding == dwarf::DW_ATE_signed_char ||
226 Encoding == dwarf::DW_ATE_float || Encoding == dwarf::DW_ATE_UTF ||
227 Encoding == dwarf::DW_ATE_boolean ||
228 Encoding == dwarf::DW_ATE_complex_float ||
229 Encoding == dwarf::DW_ATE_signed_fixed ||
230 Encoding == dwarf::DW_ATE_unsigned_fixed ||
231 (Ty->getTag() == dwarf::DW_TAG_unspecified_type &&
232 Ty->getName() == "decltype(nullptr)")) &&
233 "Unsupported encoding");
234 return Encoding == dwarf::DW_ATE_unsigned ||
235 Encoding == dwarf::DW_ATE_unsigned_char ||
236 Encoding == dwarf::DW_ATE_UTF || Encoding == dwarf::DW_ATE_boolean ||
237 Encoding == llvm::dwarf::DW_ATE_unsigned_fixed ||
238 Ty->getTag() == dwarf::DW_TAG_unspecified_type;
239}
240
241static bool hasDebugInfo(const MachineModuleInfo *MMI,
242 const MachineFunction *MF) {
243 if (!MMI->hasDebugInfo())
244 return false;
245 auto *SP = MF->getFunction().getSubprogram();
246 if (!SP)
247 return false;
248 assert(SP->getUnit());
249 auto EK = SP->getUnit()->getEmissionKind();
250 if (EK == DICompileUnit::NoDebug)
251 return false;
252 return true;
253}
254
255void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
256 PrevInstBB = nullptr;
257
258 if (!Asm || !hasDebugInfo(MMI, MF)) {
259 skippedNonDebugFunction();
260 return;
261 }
262
263 // Grab the lexical scopes for the function, if we don't have any of those
264 // then we're not going to be able to do anything.
265 LScopes.initialize(*MF);
266 if (LScopes.empty()) {
267 beginFunctionImpl(MF);
268 return;
269 }
270
271 // Make sure that each lexical scope will have a begin/end label.
272 identifyScopeMarkers();
273
274 // Calculate history for local variables.
275 assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
276 assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
277 calculateDbgEntityHistory(MF, TRI: Asm->MF->getSubtarget().getRegisterInfo(),
278 DbgValues, DbgLabels);
279 InstOrdering.initialize(MF: *MF);
280 if (TrimVarLocs)
281 DbgValues.trimLocationRanges(MF: *MF, LScopes, Ordering: InstOrdering);
282 LLVM_DEBUG(DbgValues.dump(MF->getName()));
283
284 // Request labels for the full history.
285 for (const auto &I : DbgValues) {
286 const auto &Entries = I.second;
287 if (Entries.empty())
288 continue;
289
290 auto IsDescribedByReg = [](const MachineInstr *MI) {
291 return any_of(Range: MI->debug_operands(),
292 P: [](auto &MO) { return MO.isReg() && MO.getReg(); });
293 };
294
295 // The first mention of a function argument gets the CurrentFnBegin label,
296 // so arguments are visible when breaking at function entry.
297 //
298 // We do not change the label for values that are described by registers,
299 // as that could place them above their defining instructions. We should
300 // ideally not change the labels for constant debug values either, since
301 // doing that violates the ranges that are calculated in the history map.
302 // However, we currently do not emit debug values for constant arguments
303 // directly at the start of the function, so this code is still useful.
304 const DILocalVariable *DIVar =
305 Entries.front().getInstr()->getDebugVariable();
306 if (DIVar->isParameter() &&
307 getDISubprogram(Scope: DIVar->getScope())->describes(F: &MF->getFunction())) {
308 if (!IsDescribedByReg(Entries.front().getInstr()))
309 LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
310 if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
311 // Mark all non-overlapping initial fragments.
312 for (const auto *I = Entries.begin(); I != Entries.end(); ++I) {
313 if (!I->isDbgValue())
314 continue;
315 const DIExpression *Fragment = I->getInstr()->getDebugExpression();
316 if (std::any_of(first: Entries.begin(), last: I,
317 pred: [&](DbgValueHistoryMap::Entry Pred) {
318 return Pred.isDbgValue() &&
319 Fragment->fragmentsOverlap(
320 Other: Pred.getInstr()->getDebugExpression());
321 }))
322 break;
323 // The code that generates location lists for DWARF assumes that the
324 // entries' start labels are monotonically increasing, and since we
325 // don't change the label for fragments that are described by
326 // registers, we must bail out when encountering such a fragment.
327 if (IsDescribedByReg(I->getInstr()))
328 break;
329 LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
330 }
331 }
332 }
333
334 for (const auto &Entry : Entries) {
335 if (Entry.isDbgValue())
336 requestLabelBeforeInsn(MI: Entry.getInstr());
337 else
338 requestLabelAfterInsn(MI: Entry.getInstr());
339 }
340 }
341
342 // Ensure there is a symbol before DBG_LABEL.
343 for (const auto &I : DbgLabels) {
344 const MachineInstr *MI = I.second;
345 requestLabelBeforeInsn(MI);
346 }
347
348 PrevInstLoc = DebugLoc();
349 PrevLabel = Asm->getFunctionBegin();
350 beginFunctionImpl(MF);
351}
352
353void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
354 if (!Asm || !MMI->hasDebugInfo())
355 return;
356
357 assert(CurMI == nullptr);
358 CurMI = MI;
359
360 // Insert labels where requested.
361 DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
362 LabelsBeforeInsn.find(Val: MI);
363
364 // No label needed.
365 if (I == LabelsBeforeInsn.end())
366 return;
367
368 // Label already assigned.
369 if (I->second)
370 return;
371
372 if (!PrevLabel) {
373 PrevLabel = MMI->getContext().createTempSymbol();
374 Asm->OutStreamer->emitLabel(Symbol: PrevLabel);
375 }
376 I->second = PrevLabel;
377}
378
379void DebugHandlerBase::endInstruction() {
380 if (!Asm || !MMI->hasDebugInfo())
381 return;
382
383 assert(CurMI != nullptr);
384 // Don't create a new label after DBG_VALUE and other instructions that don't
385 // generate code.
386 if (!CurMI->isMetaInstruction()) {
387 PrevLabel = nullptr;
388 PrevInstBB = CurMI->getParent();
389 }
390
391 DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
392 LabelsAfterInsn.find(Val: CurMI);
393
394 // No label needed or label already assigned.
395 if (I == LabelsAfterInsn.end() || I->second) {
396 CurMI = nullptr;
397 return;
398 }
399
400 // We need a label after this instruction. With basic block sections, just
401 // use the end symbol of the section if this is the last instruction of the
402 // section. This reduces the need for an additional label and also helps
403 // merging ranges.
404 if (CurMI->getParent()->isEndSection() && CurMI->getNextNode() == nullptr) {
405 PrevLabel = CurMI->getParent()->getEndSymbol();
406 } else if (!PrevLabel) {
407 PrevLabel = MMI->getContext().createTempSymbol();
408 Asm->OutStreamer->emitLabel(Symbol: PrevLabel);
409 }
410 I->second = PrevLabel;
411 CurMI = nullptr;
412}
413
414void DebugHandlerBase::endFunction(const MachineFunction *MF) {
415 if (Asm && hasDebugInfo(MMI, MF))
416 endFunctionImpl(MF);
417 DbgValues.clear();
418 DbgLabels.clear();
419 LabelsBeforeInsn.clear();
420 LabelsAfterInsn.clear();
421 InstOrdering.clear();
422}
423
424void DebugHandlerBase::beginBasicBlockSection(const MachineBasicBlock &MBB) {
425 EpilogBeginBlock = nullptr;
426 if (!MBB.isEntryBlock())
427 PrevLabel = MBB.getSymbol();
428}
429
430void DebugHandlerBase::endBasicBlockSection(const MachineBasicBlock &MBB) {
431 PrevLabel = nullptr;
432}
433

source code of llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp