1//===------ BPFPreserveStaticOffset.cpp -----------------------------------===//
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// TLDR: replaces llvm.preserve.static.offset + GEP + load / store
10// with llvm.bpf.getelementptr.and.load / store
11//
12// This file implements BPFPreserveStaticOffsetPass transformation.
13// This transformation address two BPF verifier specific issues:
14//
15// (a) Access to the fields of some structural types is allowed only
16// using load and store instructions with static immediate offsets.
17//
18// Examples of such types are `struct __sk_buff` and `struct
19// bpf_sock_ops`. This is so because offsets of the fields of
20// these structures do not match real offsets in the running
21// kernel. During BPF program load LDX and STX instructions
22// referring to the fields of these types are rewritten so that
23// offsets match real offsets. For this rewrite to happen field
24// offsets have to be encoded as immediate operands of the
25// instructions.
26//
27// See kernel/bpf/verifier.c:convert_ctx_access function in the
28// Linux kernel source tree for details.
29//
30// (b) Pointers to context parameters of BPF programs must not be
31// modified before access.
32//
33// During BPF program verification a tag PTR_TO_CTX is tracked for
34// register values. In case if register with such tag is modified
35// BPF program is not allowed to read or write memory using this
36// register. See kernel/bpf/verifier.c:check_mem_access function
37// in the Linux kernel source tree for details.
38//
39// The following sequence of the IR instructions:
40//
41// %x = getelementptr %ptr, %constant_offset
42// %y = load %x
43//
44// Is translated as a single machine instruction:
45//
46// LDW %ptr, %constant_offset
47//
48// In order for cases (a) and (b) to work the sequence %x-%y above has
49// to be preserved by the IR passes.
50//
51// However, several optimization passes might sink `load` instruction
52// or hoist `getelementptr` instruction so that the instructions are
53// no longer in sequence. Examples of such passes are:
54// SimplifyCFGPass, InstCombinePass, GVNPass.
55// After such modification the verifier would reject the BPF program.
56//
57// To avoid this issue the patterns like (load/store (getelementptr ...))
58// are replaced by calls to BPF specific intrinsic functions:
59// - llvm.bpf.getelementptr.and.load
60// - llvm.bpf.getelementptr.and.store
61//
62// These calls are lowered back to (load/store (getelementptr ...))
63// by BPFCheckAndAdjustIR pass right before the translation from IR to
64// machine instructions.
65//
66// The transformation is split into the following steps:
67// - When IR is generated from AST the calls to intrinsic function
68// llvm.preserve.static.offset are inserted.
69// - BPFPreserveStaticOffsetPass is executed as early as possible
70// with AllowPatial set to true, this handles marked GEP chains
71// with constant offsets.
72// - BPFPreserveStaticOffsetPass is executed at ScalarOptimizerLateEPCallback
73// with AllowPatial set to false, this handles marked GEP chains
74// with offsets that became constant after loop unrolling, e.g.
75// to handle the following code:
76//
77// struct context { int x[4]; } __attribute__((preserve_static_offset));
78//
79// struct context *ctx = ...;
80// #pragma clang loop unroll(full)
81// for (int i = 0; i < 4; ++i)
82// foo(ctx->x[i]);
83//
84// The early BPFPreserveStaticOffsetPass run is necessary to allow
85// additional GVN / CSE opportunities after functions inlining.
86// The relative order of optimization applied to function:
87// - early stage (1)
88// - ...
89// - function inlining (2)
90// - ...
91// - loop unrolling
92// - ...
93// - ScalarOptimizerLateEPCallback (3)
94//
95// When function A is inlined into function B all optimizations for A
96// are already done, while some passes remain for B. In case if
97// BPFPreserveStaticOffsetPass is done at (3) but not done at (1)
98// the code after (2) would contain a mix of
99// (load (gep %p)) and (get.and.load %p) usages:
100// - the (load (gep %p)) would come from the calling function;
101// - the (get.and.load %p) would come from the callee function.
102// Thus clobbering CSE / GVN passes done after inlining.
103
104#include "BPF.h"
105#include "BPFCORE.h"
106#include "llvm/ADT/SmallPtrSet.h"
107#include "llvm/ADT/SmallVector.h"
108#include "llvm/IR/Argument.h"
109#include "llvm/IR/Attributes.h"
110#include "llvm/IR/BasicBlock.h"
111#include "llvm/IR/Constants.h"
112#include "llvm/IR/DebugInfoMetadata.h"
113#include "llvm/IR/DiagnosticInfo.h"
114#include "llvm/IR/IRBuilder.h"
115#include "llvm/IR/InstIterator.h"
116#include "llvm/IR/Instructions.h"
117#include "llvm/IR/Intrinsics.h"
118#include "llvm/IR/IntrinsicsBPF.h"
119#include "llvm/IR/Module.h"
120#include "llvm/Support/Debug.h"
121#include "llvm/Support/ErrorHandling.h"
122
123#define DEBUG_TYPE "bpf-preserve-static-offset"
124
125using namespace llvm;
126
127static const unsigned GepAndLoadFirstIdxArg = 6;
128static const unsigned GepAndStoreFirstIdxArg = 7;
129
130static bool isIntrinsicCall(Value *I, Intrinsic::ID Id) {
131 if (auto *Call = dyn_cast<CallInst>(Val: I))
132 if (Function *Func = Call->getCalledFunction())
133 return Func->getIntrinsicID() == Id;
134 return false;
135}
136
137static bool isPreserveStaticOffsetCall(Value *I) {
138 return isIntrinsicCall(I, Id: Intrinsic::preserve_static_offset);
139}
140
141static CallInst *isGEPAndLoad(Value *I) {
142 if (isIntrinsicCall(I, Id: Intrinsic::bpf_getelementptr_and_load))
143 return cast<CallInst>(Val: I);
144 return nullptr;
145}
146
147static CallInst *isGEPAndStore(Value *I) {
148 if (isIntrinsicCall(I, Id: Intrinsic::bpf_getelementptr_and_store))
149 return cast<CallInst>(Val: I);
150 return nullptr;
151}
152
153template <class T = Instruction>
154static DILocation *mergeDILocations(SmallVector<T *> &Insns) {
155 DILocation *Merged = (*Insns.begin())->getDebugLoc();
156 for (T *I : Insns)
157 Merged = DILocation::getMergedLocation(LocA: Merged, LocB: I->getDebugLoc());
158 return Merged;
159}
160
161static CallInst *makeIntrinsicCall(Module *M,
162 Intrinsic::BPFIntrinsics Intrinsic,
163 ArrayRef<Type *> Types,
164 ArrayRef<Value *> Args) {
165
166 Function *Fn = Intrinsic::getDeclaration(M, id: Intrinsic, Tys: Types);
167 return CallInst::Create(Func: Fn, Args);
168}
169
170static void setParamElementType(CallInst *Call, unsigned ArgNo, Type *Type) {
171 LLVMContext &C = Call->getContext();
172 Call->addParamAttr(ArgNo, Attr: Attribute::get(Context&: C, Kind: Attribute::ElementType, Ty: Type));
173}
174
175static void setParamReadNone(CallInst *Call, unsigned ArgNo) {
176 LLVMContext &C = Call->getContext();
177 Call->addParamAttr(ArgNo, Attr: Attribute::get(Context&: C, Kind: Attribute::ReadNone));
178}
179
180static void setParamReadOnly(CallInst *Call, unsigned ArgNo) {
181 LLVMContext &C = Call->getContext();
182 Call->addParamAttr(ArgNo, Attr: Attribute::get(Context&: C, Kind: Attribute::ReadOnly));
183}
184
185static void setParamWriteOnly(CallInst *Call, unsigned ArgNo) {
186 LLVMContext &C = Call->getContext();
187 Call->addParamAttr(ArgNo, Attr: Attribute::get(Context&: C, Kind: Attribute::WriteOnly));
188}
189
190namespace {
191struct GEPChainInfo {
192 bool InBounds;
193 Type *SourceElementType;
194 SmallVector<Value *> Indices;
195 SmallVector<GetElementPtrInst *> Members;
196
197 GEPChainInfo() { reset(); }
198
199 void reset() {
200 InBounds = true;
201 SourceElementType = nullptr;
202 Indices.clear();
203 Members.clear();
204 }
205};
206} // Anonymous namespace
207
208template <class T = std::disjunction<LoadInst, StoreInst>>
209static void fillCommonArgs(LLVMContext &C, SmallVector<Value *> &Args,
210 GEPChainInfo &GEP, T *Insn) {
211 Type *Int8Ty = Type::getInt8Ty(C);
212 Type *Int1Ty = Type::getInt1Ty(C);
213 // Implementation of Align guarantees that ShiftValue < 64
214 unsigned AlignShiftValue = Log2_64(Insn->getAlign().value());
215 Args.push_back(Elt: GEP.Members[0]->getPointerOperand());
216 Args.push_back(Elt: ConstantInt::get(Int1Ty, Insn->isVolatile()));
217 Args.push_back(Elt: ConstantInt::get(Ty: Int8Ty, V: (unsigned)Insn->getOrdering()));
218 Args.push_back(Elt: ConstantInt::get(Ty: Int8Ty, V: (unsigned)Insn->getSyncScopeID()));
219 Args.push_back(Elt: ConstantInt::get(Ty: Int8Ty, V: AlignShiftValue));
220 Args.push_back(Elt: ConstantInt::get(Ty: Int1Ty, V: GEP.InBounds));
221 Args.append(in_start: GEP.Indices.begin(), in_end: GEP.Indices.end());
222}
223
224static Instruction *makeGEPAndLoad(Module *M, GEPChainInfo &GEP,
225 LoadInst *Load) {
226 SmallVector<Value *> Args;
227 fillCommonArgs(C&: M->getContext(), Args, GEP, Insn: Load);
228 CallInst *Call = makeIntrinsicCall(M, Intrinsic: Intrinsic::bpf_getelementptr_and_load,
229 Types: {Load->getType()}, Args);
230 setParamElementType(Call, ArgNo: 0, Type: GEP.SourceElementType);
231 Call->applyMergedLocation(LocA: mergeDILocations(Insns&: GEP.Members), LocB: Load->getDebugLoc());
232 Call->setName((*GEP.Members.rbegin())->getName());
233 if (Load->isUnordered()) {
234 Call->setOnlyReadsMemory();
235 Call->setOnlyAccessesArgMemory();
236 setParamReadOnly(Call, ArgNo: 0);
237 }
238 for (unsigned I = GepAndLoadFirstIdxArg; I < Args.size(); ++I)
239 Call->addParamAttr(ArgNo: I, Kind: Attribute::ImmArg);
240 Call->setAAMetadata(Load->getAAMetadata());
241 return Call;
242}
243
244static Instruction *makeGEPAndStore(Module *M, GEPChainInfo &GEP,
245 StoreInst *Store) {
246 SmallVector<Value *> Args;
247 Args.push_back(Elt: Store->getValueOperand());
248 fillCommonArgs(C&: M->getContext(), Args, GEP, Insn: Store);
249 CallInst *Call =
250 makeIntrinsicCall(M, Intrinsic: Intrinsic::bpf_getelementptr_and_store,
251 Types: {Store->getValueOperand()->getType()}, Args);
252 setParamElementType(Call, ArgNo: 1, Type: GEP.SourceElementType);
253 if (Store->getValueOperand()->getType()->isPointerTy())
254 setParamReadNone(Call, ArgNo: 0);
255 Call->applyMergedLocation(LocA: mergeDILocations(Insns&: GEP.Members),
256 LocB: Store->getDebugLoc());
257 if (Store->isUnordered()) {
258 Call->setOnlyWritesMemory();
259 Call->setOnlyAccessesArgMemory();
260 setParamWriteOnly(Call, ArgNo: 1);
261 }
262 for (unsigned I = GepAndStoreFirstIdxArg; I < Args.size(); ++I)
263 Call->addParamAttr(ArgNo: I, Kind: Attribute::ImmArg);
264 Call->setAAMetadata(Store->getAAMetadata());
265 return Call;
266}
267
268static unsigned getOperandAsUnsigned(CallInst *Call, unsigned ArgNo) {
269 if (auto *Int = dyn_cast<ConstantInt>(Val: Call->getOperand(i_nocapture: ArgNo)))
270 return Int->getValue().getZExtValue();
271 std::string Report;
272 raw_string_ostream ReportS(Report);
273 ReportS << "Expecting ConstantInt as argument #" << ArgNo << " of " << *Call
274 << "\n";
275 report_fatal_error(reason: StringRef(Report));
276}
277
278static GetElementPtrInst *reconstructGEP(CallInst *Call, int Delta) {
279 SmallVector<Value *> Indices;
280 Indices.append(in_start: Call->data_operands_begin() + 6 + Delta,
281 in_end: Call->data_operands_end());
282 Type *GEPPointeeType = Call->getParamElementType(ArgNo: Delta);
283 auto *GEP =
284 GetElementPtrInst::Create(PointeeType: GEPPointeeType, Ptr: Call->getOperand(i_nocapture: Delta),
285 IdxList: ArrayRef<Value *>(Indices), NameStr: Call->getName());
286 GEP->setIsInBounds(getOperandAsUnsigned(Call, ArgNo: 5 + Delta));
287 return GEP;
288}
289
290template <class T = std::disjunction<LoadInst, StoreInst>>
291static void reconstructCommon(CallInst *Call, GetElementPtrInst *GEP, T *Insn,
292 int Delta) {
293 Insn->setVolatile(getOperandAsUnsigned(Call, ArgNo: 1 + Delta));
294 Insn->setOrdering((AtomicOrdering)getOperandAsUnsigned(Call, ArgNo: 2 + Delta));
295 Insn->setSyncScopeID(getOperandAsUnsigned(Call, ArgNo: 3 + Delta));
296 unsigned AlignShiftValue = getOperandAsUnsigned(Call, ArgNo: 4 + Delta);
297 Insn->setAlignment(Align(1ULL << AlignShiftValue));
298 GEP->setDebugLoc(Call->getDebugLoc());
299 Insn->setDebugLoc(Call->getDebugLoc());
300 Insn->setAAMetadata(Call->getAAMetadata());
301}
302
303std::pair<GetElementPtrInst *, LoadInst *>
304BPFPreserveStaticOffsetPass::reconstructLoad(CallInst *Call) {
305 GetElementPtrInst *GEP = reconstructGEP(Call, Delta: 0);
306 Type *ReturnType = Call->getFunctionType()->getReturnType();
307 auto *Load = new LoadInst(ReturnType, GEP, "",
308 /* These would be set in reconstructCommon */
309 false, Align(1));
310 reconstructCommon(Call, GEP, Insn: Load, Delta: 0);
311 return std::pair{GEP, Load};
312}
313
314std::pair<GetElementPtrInst *, StoreInst *>
315BPFPreserveStaticOffsetPass::reconstructStore(CallInst *Call) {
316 GetElementPtrInst *GEP = reconstructGEP(Call, Delta: 1);
317 auto *Store = new StoreInst(Call->getOperand(i_nocapture: 0), GEP,
318 /* These would be set in reconstructCommon */
319 false, Align(1));
320 reconstructCommon(Call, GEP, Insn: Store, Delta: 1);
321 return std::pair{GEP, Store};
322}
323
324static bool isZero(Value *V) {
325 auto *CI = dyn_cast<ConstantInt>(Val: V);
326 return CI && CI->isZero();
327}
328
329// Given a chain of GEP instructions collect information necessary to
330// merge this chain as a single GEP instruction of form:
331// getelementptr %<type>, ptr %p, i32 0, <field_idx1>, <field_idx2>, ...
332static bool foldGEPChainAsStructAccess(SmallVector<GetElementPtrInst *> &GEPs,
333 GEPChainInfo &Info) {
334 if (GEPs.empty())
335 return false;
336
337 if (!all_of(Range&: GEPs, P: [=](GetElementPtrInst *GEP) {
338 return GEP->hasAllConstantIndices();
339 }))
340 return false;
341
342 GetElementPtrInst *First = GEPs[0];
343 Info.InBounds = First->isInBounds();
344 Info.SourceElementType = First->getSourceElementType();
345 Type *ResultElementType = First->getResultElementType();
346 Info.Indices.append(in_start: First->idx_begin(), in_end: First->idx_end());
347 Info.Members.push_back(Elt: First);
348
349 for (auto *Iter = GEPs.begin() + 1; Iter != GEPs.end(); ++Iter) {
350 GetElementPtrInst *GEP = *Iter;
351 if (!isZero(V: *GEP->idx_begin())) {
352 Info.reset();
353 return false;
354 }
355 if (!GEP->getSourceElementType() ||
356 GEP->getSourceElementType() != ResultElementType) {
357 Info.reset();
358 return false;
359 }
360 Info.InBounds &= GEP->isInBounds();
361 Info.Indices.append(in_start: GEP->idx_begin() + 1, in_end: GEP->idx_end());
362 Info.Members.push_back(Elt: GEP);
363 ResultElementType = GEP->getResultElementType();
364 }
365
366 return true;
367}
368
369// Given a chain of GEP instructions collect information necessary to
370// merge this chain as a single GEP instruction of form:
371// getelementptr i8, ptr %p, i64 %offset
372static bool foldGEPChainAsU8Access(SmallVector<GetElementPtrInst *> &GEPs,
373 GEPChainInfo &Info) {
374 if (GEPs.empty())
375 return false;
376
377 GetElementPtrInst *First = GEPs[0];
378 const DataLayout &DL = First->getDataLayout();
379 LLVMContext &C = First->getContext();
380 Type *PtrTy = First->getType()->getScalarType();
381 APInt Offset(DL.getIndexTypeSizeInBits(Ty: PtrTy), 0);
382 for (GetElementPtrInst *GEP : GEPs) {
383 if (!GEP->accumulateConstantOffset(DL, Offset)) {
384 Info.reset();
385 return false;
386 }
387 Info.InBounds &= GEP->isInBounds();
388 Info.Members.push_back(Elt: GEP);
389 }
390 Info.SourceElementType = Type::getInt8Ty(C);
391 Info.Indices.push_back(Elt: ConstantInt::get(Context&: C, V: Offset));
392
393 return true;
394}
395
396static void reportNonStaticGEPChain(Instruction *Insn) {
397 auto Msg = DiagnosticInfoUnsupported(
398 *Insn->getFunction(),
399 Twine("Non-constant offset in access to a field of a type marked "
400 "with preserve_static_offset might be rejected by BPF verifier")
401 .concat(Suffix: Insn->getDebugLoc()
402 ? ""
403 : " (pass -g option to get exact location)"),
404 Insn->getDebugLoc(), DS_Warning);
405 Insn->getContext().diagnose(DI: Msg);
406}
407
408static bool allZeroIndices(SmallVector<GetElementPtrInst *> &GEPs) {
409 return GEPs.empty() || all_of(Range&: GEPs, P: [=](GetElementPtrInst *GEP) {
410 return GEP->hasAllZeroIndices();
411 });
412}
413
414static bool tryToReplaceWithGEPBuiltin(Instruction *LoadOrStoreTemplate,
415 SmallVector<GetElementPtrInst *> &GEPs,
416 Instruction *InsnToReplace) {
417 GEPChainInfo GEPChain;
418 if (!foldGEPChainAsStructAccess(GEPs, Info&: GEPChain) &&
419 !foldGEPChainAsU8Access(GEPs, Info&: GEPChain)) {
420 return false;
421 }
422 Module *M = InsnToReplace->getModule();
423 if (auto *Load = dyn_cast<LoadInst>(Val: LoadOrStoreTemplate)) {
424 Instruction *Replacement = makeGEPAndLoad(M, GEP&: GEPChain, Load);
425 Replacement->insertBefore(InsertPos: InsnToReplace);
426 InsnToReplace->replaceAllUsesWith(V: Replacement);
427 }
428 if (auto *Store = dyn_cast<StoreInst>(Val: LoadOrStoreTemplate)) {
429 Instruction *Replacement = makeGEPAndStore(M, GEP&: GEPChain, Store);
430 Replacement->insertBefore(InsertPos: InsnToReplace);
431 }
432 return true;
433}
434
435// Check if U->getPointerOperand() == I
436static bool isPointerOperand(Value *I, User *U) {
437 if (auto *L = dyn_cast<LoadInst>(Val: U))
438 return L->getPointerOperand() == I;
439 if (auto *S = dyn_cast<StoreInst>(Val: U))
440 return S->getPointerOperand() == I;
441 if (auto *GEP = dyn_cast<GetElementPtrInst>(Val: U))
442 return GEP->getPointerOperand() == I;
443 if (auto *Call = isGEPAndLoad(I: U))
444 return Call->getArgOperand(i: 0) == I;
445 if (auto *Call = isGEPAndStore(I: U))
446 return Call->getArgOperand(i: 1) == I;
447 return false;
448}
449
450static bool isInlineableCall(User *U) {
451 if (auto *Call = dyn_cast<CallInst>(Val: U))
452 return Call->hasFnAttr(Kind: Attribute::InlineHint);
453 return false;
454}
455
456static void rewriteAccessChain(Instruction *Insn,
457 SmallVector<GetElementPtrInst *> &GEPs,
458 SmallVector<Instruction *> &Visited,
459 bool AllowPatial, bool &StillUsed);
460
461static void rewriteUses(Instruction *Insn,
462 SmallVector<GetElementPtrInst *> &GEPs,
463 SmallVector<Instruction *> &Visited, bool AllowPatial,
464 bool &StillUsed) {
465 for (User *U : Insn->users()) {
466 auto *UI = dyn_cast<Instruction>(Val: U);
467 if (UI && (isPointerOperand(I: Insn, U: UI) || isPreserveStaticOffsetCall(I: UI) ||
468 isInlineableCall(U: UI)))
469 rewriteAccessChain(Insn: UI, GEPs, Visited, AllowPatial, StillUsed);
470 else
471 LLVM_DEBUG({
472 llvm::dbgs() << "unsupported usage in BPFPreserveStaticOffsetPass:\n";
473 llvm::dbgs() << " Insn: " << *Insn << "\n";
474 llvm::dbgs() << " User: " << *U << "\n";
475 });
476 }
477}
478
479// A DFS traversal of GEP chain trees starting from Root.
480//
481// Recursion descends through GEP instructions and
482// llvm.preserve.static.offset calls. Recursion stops at any other
483// instruction. If load or store instruction is reached it is replaced
484// by a call to `llvm.bpf.getelementptr.and.load` or
485// `llvm.bpf.getelementptr.and.store` intrinsic.
486// If `llvm.bpf.getelementptr.and.load/store` is reached the accumulated
487// GEPs are merged into the intrinsic call.
488// If nested calls to `llvm.preserve.static.offset` are encountered these
489// calls are marked for deletion.
490//
491// Parameters description:
492// - Insn - current position in the tree
493// - GEPs - GEP instructions for the current branch
494// - Visited - a list of visited instructions in DFS order,
495// order is important for unused instruction deletion.
496// - AllowPartial - when true GEP chains that can't be folded are
497// not reported, otherwise diagnostic message is show for such chains.
498// - StillUsed - set to true if one of the GEP chains could not be
499// folded, makes sense when AllowPartial is false, means that root
500// preserve.static.offset call is still in use and should remain
501// until the next run of this pass.
502static void rewriteAccessChain(Instruction *Insn,
503 SmallVector<GetElementPtrInst *> &GEPs,
504 SmallVector<Instruction *> &Visited,
505 bool AllowPatial, bool &StillUsed) {
506 auto MarkAndTraverseUses = [&]() {
507 Visited.push_back(Elt: Insn);
508 rewriteUses(Insn, GEPs, Visited, AllowPatial, StillUsed);
509 };
510 auto TryToReplace = [&](Instruction *LoadOrStore) {
511 // Do nothing for (preserve.static.offset (load/store ..)) or for
512 // GEPs with zero indices. Such constructs lead to zero offset and
513 // are simplified by other passes.
514 if (allZeroIndices(GEPs))
515 return;
516 if (tryToReplaceWithGEPBuiltin(LoadOrStoreTemplate: LoadOrStore, GEPs, InsnToReplace: Insn)) {
517 Visited.push_back(Elt: Insn);
518 return;
519 }
520 if (!AllowPatial)
521 reportNonStaticGEPChain(Insn);
522 StillUsed = true;
523 };
524 if (isa<LoadInst>(Val: Insn) || isa<StoreInst>(Val: Insn)) {
525 TryToReplace(Insn);
526 } else if (isGEPAndLoad(I: Insn)) {
527 auto [GEP, Load] =
528 BPFPreserveStaticOffsetPass::reconstructLoad(Call: cast<CallInst>(Val: Insn));
529 GEPs.push_back(Elt: GEP);
530 TryToReplace(Load);
531 GEPs.pop_back();
532 delete Load;
533 delete GEP;
534 } else if (isGEPAndStore(I: Insn)) {
535 // This case can't be merged with the above because
536 // `delete Load` / `delete Store` wants a concrete type,
537 // destructor of Instruction is protected.
538 auto [GEP, Store] =
539 BPFPreserveStaticOffsetPass::reconstructStore(Call: cast<CallInst>(Val: Insn));
540 GEPs.push_back(Elt: GEP);
541 TryToReplace(Store);
542 GEPs.pop_back();
543 delete Store;
544 delete GEP;
545 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(Val: Insn)) {
546 GEPs.push_back(Elt: GEP);
547 MarkAndTraverseUses();
548 GEPs.pop_back();
549 } else if (isPreserveStaticOffsetCall(I: Insn)) {
550 MarkAndTraverseUses();
551 } else if (isInlineableCall(U: Insn)) {
552 // Preserve preserve.static.offset call for parameters of
553 // functions that might be inlined. These would be removed on a
554 // second pass after inlining.
555 // Might happen when a pointer to a preserve_static_offset
556 // structure is passed as parameter of a function that would be
557 // inlined inside a loop that would be unrolled.
558 if (AllowPatial)
559 StillUsed = true;
560 } else {
561 SmallString<128> Buf;
562 raw_svector_ostream BufStream(Buf);
563 BufStream << *Insn;
564 report_fatal_error(
565 reason: Twine("Unexpected rewriteAccessChain Insn = ").concat(Suffix: Buf));
566 }
567}
568
569static void removeMarkerCall(Instruction *Marker) {
570 Marker->replaceAllUsesWith(V: Marker->getOperand(i: 0));
571 Marker->eraseFromParent();
572}
573
574static bool rewriteAccessChain(Instruction *Marker, bool AllowPatial,
575 SmallPtrSetImpl<Instruction *> &RemovedMarkers) {
576 SmallVector<GetElementPtrInst *> GEPs;
577 SmallVector<Instruction *> Visited;
578 bool StillUsed = false;
579 rewriteUses(Insn: Marker, GEPs, Visited, AllowPatial, StillUsed);
580 // Check if Visited instructions could be removed, iterate in
581 // reverse to unblock instructions higher in the chain.
582 for (auto V = Visited.rbegin(); V != Visited.rend(); ++V) {
583 if (isPreserveStaticOffsetCall(I: *V)) {
584 removeMarkerCall(Marker: *V);
585 RemovedMarkers.insert(Ptr: *V);
586 } else if ((*V)->use_empty()) {
587 (*V)->eraseFromParent();
588 }
589 }
590 return StillUsed;
591}
592
593static std::vector<Instruction *>
594collectPreserveStaticOffsetCalls(Function &F) {
595 std::vector<Instruction *> Calls;
596 for (Instruction &Insn : instructions(F))
597 if (isPreserveStaticOffsetCall(I: &Insn))
598 Calls.push_back(x: &Insn);
599 return Calls;
600}
601
602bool isPreserveArrayIndex(Value *V) {
603 return isIntrinsicCall(I: V, Id: Intrinsic::preserve_array_access_index);
604}
605
606bool isPreserveStructIndex(Value *V) {
607 return isIntrinsicCall(I: V, Id: Intrinsic::preserve_struct_access_index);
608}
609
610bool isPreserveUnionIndex(Value *V) {
611 return isIntrinsicCall(I: V, Id: Intrinsic::preserve_union_access_index);
612}
613
614static void removePAICalls(Instruction *Marker) {
615 auto IsPointerOperand = [](Value *Op, User *U) {
616 if (auto *GEP = dyn_cast<GetElementPtrInst>(Val: U))
617 return GEP->getPointerOperand() == Op;
618 if (isPreserveStaticOffsetCall(I: U) || isPreserveArrayIndex(V: U) ||
619 isPreserveStructIndex(V: U) || isPreserveUnionIndex(V: U))
620 return cast<CallInst>(Val: U)->getArgOperand(i: 0) == Op;
621 return false;
622 };
623
624 SmallVector<Value *, 32> WorkList;
625 WorkList.push_back(Elt: Marker);
626 do {
627 Value *V = WorkList.pop_back_val();
628 for (User *U : V->users())
629 if (IsPointerOperand(V, U))
630 WorkList.push_back(Elt: U);
631 auto *Call = dyn_cast<CallInst>(Val: V);
632 if (!Call)
633 continue;
634 if (isPreserveArrayIndex(V))
635 BPFCoreSharedInfo::removeArrayAccessCall(Call);
636 else if (isPreserveStructIndex(V))
637 BPFCoreSharedInfo::removeStructAccessCall(Call);
638 else if (isPreserveUnionIndex(V))
639 BPFCoreSharedInfo::removeUnionAccessCall(Call);
640 } while (!WorkList.empty());
641}
642
643// Look for sequences:
644// - llvm.preserve.static.offset -> getelementptr... -> load
645// - llvm.preserve.static.offset -> getelementptr... -> store
646// And replace those with calls to intrinsics:
647// - llvm.bpf.getelementptr.and.load
648// - llvm.bpf.getelementptr.and.store
649static bool rewriteFunction(Function &F, bool AllowPartial) {
650 LLVM_DEBUG(dbgs() << "********** BPFPreserveStaticOffsetPass (AllowPartial="
651 << AllowPartial << ") ************\n");
652
653 auto MarkerCalls = collectPreserveStaticOffsetCalls(F);
654 SmallPtrSet<Instruction *, 16> RemovedMarkers;
655
656 LLVM_DEBUG(dbgs() << "There are " << MarkerCalls.size()
657 << " preserve.static.offset calls\n");
658
659 if (MarkerCalls.empty())
660 return false;
661
662 for (auto *Call : MarkerCalls)
663 removePAICalls(Marker: Call);
664
665 for (auto *Call : MarkerCalls) {
666 if (RemovedMarkers.contains(Ptr: Call))
667 continue;
668 bool StillUsed = rewriteAccessChain(Marker: Call, AllowPatial: AllowPartial, RemovedMarkers);
669 if (!StillUsed || !AllowPartial)
670 removeMarkerCall(Marker: Call);
671 }
672
673 return true;
674}
675
676PreservedAnalyses
677llvm::BPFPreserveStaticOffsetPass::run(Function &F,
678 FunctionAnalysisManager &AM) {
679 return rewriteFunction(F, AllowPartial) ? PreservedAnalyses::none()
680 : PreservedAnalyses::all();
681}
682