1 //===--- SemaStmtAttr.cpp - Statement Attribute Handling ------------------===//
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 implements stmt-related attribute processing.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "clang/AST/EvaluatedExprVisitor.h"
14 #include "clang/Sema/SemaInternal.h"
15 #include "clang/AST/ASTContext.h"
16 #include "clang/Basic/SourceManager.h"
17 #include "clang/Sema/DelayedDiagnostic.h"
18 #include "clang/Sema/Lookup.h"
19 #include "clang/Sema/ScopeInfo.h"
20 #include "llvm/ADT/StringExtras.h"
21 
22 using namespace clang;
23 using namespace sema;
24 
25 static Attr *handleFallThroughAttr(Sema &S, Stmt *St, const ParsedAttr &A,
26                                    SourceRange Range) {
27   FallThroughAttr Attr(S.Context, A);
28   if (!isa<NullStmt>(St)) {
29     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_wrong_target)
30         << Attr.getSpelling() << St->getBeginLoc();
31     if (isa<SwitchCase>(St)) {
32       SourceLocation L = S.getLocForEndOfToken(Range.getEnd());
33       S.Diag(L, diag::note_fallthrough_insert_semi_fixit)
34           << FixItHint::CreateInsertion(L, ";");
35     }
36     return nullptr;
37   }
38   auto *FnScope = S.getCurFunction();
39   if (FnScope->SwitchStack.empty()) {
40     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_outside_switch);
41     return nullptr;
42   }
43 
44   // If this is spelled as the standard C++17 attribute, but not in C++17, warn
45   // about using it as an extension.
46   if (!S.getLangOpts().CPlusPlus17 && A.isCXX11Attribute() &&
47       !A.getScopeName())
48     S.Diag(A.getLoc(), diag::ext_cxx17_attr) << A;
49 
50   FnScope->setHasFallthroughStmt();
51   return ::new (S.Context) FallThroughAttr(S.Context, A);
52 }
53 
54 static Attr *handleSuppressAttr(Sema &S, Stmt *St, const ParsedAttr &A,
55                                 SourceRange Range) {
56   if (A.getNumArgs() < 1) {
57     S.Diag(A.getLoc(), diag::err_attribute_too_few_arguments) << A << 1;
58     return nullptr;
59   }
60 
61   std::vector<StringRef> DiagnosticIdentifiers;
62   for (unsigned I = 0, E = A.getNumArgs(); I != E; ++I) {
63     StringRef RuleName;
64 
65     if (!S.checkStringLiteralArgumentAttr(A, I, RuleName, nullptr))
66       return nullptr;
67 
68     // FIXME: Warn if the rule name is unknown. This is tricky because only
69     // clang-tidy knows about available rules.
70     DiagnosticIdentifiers.push_back(RuleName);
71   }
72 
73   return ::new (S.Context) SuppressAttr(
74       S.Context, A, DiagnosticIdentifiers.data(), DiagnosticIdentifiers.size());
75 }
76 
77 static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
78                                 SourceRange) {
79   IdentifierLoc *PragmaNameLoc = A.getArgAsIdent(0);
80   IdentifierLoc *OptionLoc = A.getArgAsIdent(1);
81   IdentifierLoc *StateLoc = A.getArgAsIdent(2);
82   Expr *ValueExpr = A.getArgAsExpr(3);
83 
84   StringRef PragmaName =
85       llvm::StringSwitch<StringRef>(PragmaNameLoc->Ident->getName())
86           .Cases("unroll", "nounroll", "unroll_and_jam", "nounroll_and_jam",
87                  PragmaNameLoc->Ident->getName())
88           .Default("clang loop");
89 
90   if (St->getStmtClass() != Stmt::DoStmtClass &&
91       St->getStmtClass() != Stmt::ForStmtClass &&
92       St->getStmtClass() != Stmt::CXXForRangeStmtClass &&
93       St->getStmtClass() != Stmt::WhileStmtClass) {
94     std::string Pragma = "#pragma " + std::string(PragmaName);
95     S.Diag(St->getBeginLoc(), diag::err_pragma_loop_precedes_nonloop) << Pragma;
96     return nullptr;
97   }
98 
99   LoopHintAttr::OptionType Option;
100   LoopHintAttr::LoopHintState State;
101 
102   auto SetHints = [&Option, &State](LoopHintAttr::OptionType O,
103                                     LoopHintAttr::LoopHintState S) {
104     Option = O;
105     State = S;
106   };
107 
108   if (PragmaName == "nounroll") {
109     SetHints(LoopHintAttr::Unroll, LoopHintAttr::Disable);
110   } else if (PragmaName == "unroll") {
111     // #pragma unroll N
112     if (ValueExpr)
113       SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Numeric);
114     else
115       SetHints(LoopHintAttr::Unroll, LoopHintAttr::Enable);
116   } else if (PragmaName == "nounroll_and_jam") {
117     SetHints(LoopHintAttr::UnrollAndJam, LoopHintAttr::Disable);
118   } else if (PragmaName == "unroll_and_jam") {
119     // #pragma unroll_and_jam N
120     if (ValueExpr)
121       SetHints(LoopHintAttr::UnrollAndJamCount, LoopHintAttr::Numeric);
122     else
123       SetHints(LoopHintAttr::UnrollAndJam, LoopHintAttr::Enable);
124   } else {
125     // #pragma clang loop ...
126     assert(OptionLoc && OptionLoc->Ident &&
127            "Attribute must have valid option info.");
128     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
129                  OptionLoc->Ident->getName())
130                  .Case("vectorize", LoopHintAttr::Vectorize)
131                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
132                  .Case("interleave", LoopHintAttr::Interleave)
133                  .Case("vectorize_predicate", LoopHintAttr::VectorizePredicate)
134                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
135                  .Case("unroll", LoopHintAttr::Unroll)
136                  .Case("unroll_count", LoopHintAttr::UnrollCount)
137                  .Case("pipeline", LoopHintAttr::PipelineDisabled)
138                  .Case("pipeline_initiation_interval",
139                        LoopHintAttr::PipelineInitiationInterval)
140                  .Case("distribute", LoopHintAttr::Distribute)
141                  .Default(LoopHintAttr::Vectorize);
142     if (Option == LoopHintAttr::VectorizeWidth ||
143         Option == LoopHintAttr::InterleaveCount ||
144         Option == LoopHintAttr::UnrollCount ||
145         Option == LoopHintAttr::PipelineInitiationInterval) {
146       assert(ValueExpr && "Attribute must have a valid value expression.");
147       if (S.CheckLoopHintExpr(ValueExpr, St->getBeginLoc()))
148         return nullptr;
149       State = LoopHintAttr::Numeric;
150     } else if (Option == LoopHintAttr::Vectorize ||
151                Option == LoopHintAttr::Interleave ||
152                Option == LoopHintAttr::VectorizePredicate ||
153                Option == LoopHintAttr::Unroll ||
154                Option == LoopHintAttr::Distribute ||
155                Option == LoopHintAttr::PipelineDisabled) {
156       assert(StateLoc && StateLoc->Ident && "Loop hint must have an argument");
157       if (StateLoc->Ident->isStr("disable"))
158         State = LoopHintAttr::Disable;
159       else if (StateLoc->Ident->isStr("assume_safety"))
160         State = LoopHintAttr::AssumeSafety;
161       else if (StateLoc->Ident->isStr("full"))
162         State = LoopHintAttr::Full;
163       else if (StateLoc->Ident->isStr("enable"))
164         State = LoopHintAttr::Enable;
165       else
166         llvm_unreachable("bad loop hint argument");
167     } else
168       llvm_unreachable("bad loop hint");
169   }
170 
171   return LoopHintAttr::CreateImplicit(S.Context, Option, State, ValueExpr, A);
172 }
173 
174 namespace {
175 class CallExprFinder : public ConstEvaluatedExprVisitor<CallExprFinder> {
176   bool FoundCallExpr = false;
177 
178 public:
179   typedef ConstEvaluatedExprVisitor<CallExprFinder> Inherited;
180 
181   CallExprFinder(Sema &S, const Stmt *St) : Inherited(S.Context) { Visit(St); }
182 
183   bool foundCallExpr() { return FoundCallExpr; }
184 
185   void VisitCallExpr(const CallExpr *E) { FoundCallExpr = true; }
186   void VisitAsmStmt(const AsmStmt *S) { FoundCallExpr = true; }
187 
188   void Visit(const Stmt *St) {
189     if (!St)
190       return;
191     ConstEvaluatedExprVisitor<CallExprFinder>::Visit(St);
192   }
193 };
194 } // namespace
195 
196 static Attr *handleNoMergeAttr(Sema &S, Stmt *St, const ParsedAttr &A,
197                                SourceRange Range) {
198   NoMergeAttr NMA(S.Context, A);
199   if (S.CheckAttrNoArgs(A))
200     return nullptr;
201 
202   CallExprFinder CEF(S, St);
203 
204   if (!CEF.foundCallExpr()) {
205     S.Diag(St->getBeginLoc(), diag::warn_nomerge_attribute_ignored_in_stmt)
206         << NMA.getSpelling();
207     return nullptr;
208   }
209 
210   return ::new (S.Context) NoMergeAttr(S.Context, A);
211 }
212 
213 static void
214 CheckForIncompatibleAttributes(Sema &S,
215                                const SmallVectorImpl<const Attr *> &Attrs) {
216   // There are 6 categories of loop hints attributes: vectorize, interleave,
217   // unroll, unroll_and_jam, pipeline and distribute. Except for distribute they
218   // come in two variants: a state form and a numeric form.  The state form
219   // selectively defaults/enables/disables the transformation for the loop
220   // (for unroll, default indicates full unrolling rather than enabling the
221   // transformation). The numeric form form provides an integer hint (for
222   // example, unroll count) to the transformer. The following array accumulates
223   // the hints encountered while iterating through the attributes to check for
224   // compatibility.
225   struct {
226     const LoopHintAttr *StateAttr;
227     const LoopHintAttr *NumericAttr;
228   } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
229                    {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
230                    {nullptr, nullptr}};
231 
232   for (const auto *I : Attrs) {
233     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
234 
235     // Skip non loop hint attributes
236     if (!LH)
237       continue;
238 
239     LoopHintAttr::OptionType Option = LH->getOption();
240     enum {
241       Vectorize,
242       Interleave,
243       Unroll,
244       UnrollAndJam,
245       Distribute,
246       Pipeline,
247       VectorizePredicate
248     } Category;
249     switch (Option) {
250     case LoopHintAttr::Vectorize:
251     case LoopHintAttr::VectorizeWidth:
252       Category = Vectorize;
253       break;
254     case LoopHintAttr::Interleave:
255     case LoopHintAttr::InterleaveCount:
256       Category = Interleave;
257       break;
258     case LoopHintAttr::Unroll:
259     case LoopHintAttr::UnrollCount:
260       Category = Unroll;
261       break;
262     case LoopHintAttr::UnrollAndJam:
263     case LoopHintAttr::UnrollAndJamCount:
264       Category = UnrollAndJam;
265       break;
266     case LoopHintAttr::Distribute:
267       // Perform the check for duplicated 'distribute' hints.
268       Category = Distribute;
269       break;
270     case LoopHintAttr::PipelineDisabled:
271     case LoopHintAttr::PipelineInitiationInterval:
272       Category = Pipeline;
273       break;
274     case LoopHintAttr::VectorizePredicate:
275       Category = VectorizePredicate;
276       break;
277     };
278 
279     assert(Category < sizeof(HintAttrs) / sizeof(HintAttrs[0]));
280     auto &CategoryState = HintAttrs[Category];
281     const LoopHintAttr *PrevAttr;
282     if (Option == LoopHintAttr::Vectorize ||
283         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
284         Option == LoopHintAttr::UnrollAndJam ||
285         Option == LoopHintAttr::VectorizePredicate ||
286         Option == LoopHintAttr::PipelineDisabled ||
287         Option == LoopHintAttr::Distribute) {
288       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
289       PrevAttr = CategoryState.StateAttr;
290       CategoryState.StateAttr = LH;
291     } else {
292       // Numeric hint.  For example, vectorize_width(8).
293       PrevAttr = CategoryState.NumericAttr;
294       CategoryState.NumericAttr = LH;
295     }
296 
297     PrintingPolicy Policy(S.Context.getLangOpts());
298     SourceLocation OptionLoc = LH->getRange().getBegin();
299     if (PrevAttr)
300       // Cannot specify same type of attribute twice.
301       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
302           << /*Duplicate=*/true << PrevAttr->getDiagnosticName(Policy)
303           << LH->getDiagnosticName(Policy);
304 
305     if (CategoryState.StateAttr && CategoryState.NumericAttr &&
306         (Category == Unroll || Category == UnrollAndJam ||
307          CategoryState.StateAttr->getState() == LoopHintAttr::Disable)) {
308       // Disable hints are not compatible with numeric hints of the same
309       // category.  As a special case, numeric unroll hints are also not
310       // compatible with enable or full form of the unroll pragma because these
311       // directives indicate full unrolling.
312       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
313           << /*Duplicate=*/false
314           << CategoryState.StateAttr->getDiagnosticName(Policy)
315           << CategoryState.NumericAttr->getDiagnosticName(Policy);
316     }
317   }
318 }
319 
320 static Attr *handleOpenCLUnrollHint(Sema &S, Stmt *St, const ParsedAttr &A,
321                                     SourceRange Range) {
322   // Although the feature was introduced only in OpenCL C v2.0 s6.11.5, it's
323   // useful for OpenCL 1.x too and doesn't require HW support.
324   // opencl_unroll_hint can have 0 arguments (compiler
325   // determines unrolling factor) or 1 argument (the unroll factor provided
326   // by the user).
327 
328   unsigned NumArgs = A.getNumArgs();
329 
330   if (NumArgs > 1) {
331     S.Diag(A.getLoc(), diag::err_attribute_too_many_arguments) << A << 1;
332     return nullptr;
333   }
334 
335   unsigned UnrollFactor = 0;
336 
337   if (NumArgs == 1) {
338     Expr *E = A.getArgAsExpr(0);
339     Optional<llvm::APSInt> ArgVal;
340 
341     if (!(ArgVal = E->getIntegerConstantExpr(S.Context))) {
342       S.Diag(A.getLoc(), diag::err_attribute_argument_type)
343           << A << AANT_ArgumentIntegerConstant << E->getSourceRange();
344       return nullptr;
345     }
346 
347     int Val = ArgVal->getSExtValue();
348 
349     if (Val <= 0) {
350       S.Diag(A.getRange().getBegin(),
351              diag::err_attribute_requires_positive_integer)
352           << A << /* positive */ 0;
353       return nullptr;
354     }
355     UnrollFactor = Val;
356   }
357 
358   return OpenCLUnrollHintAttr::CreateImplicit(S.Context, UnrollFactor);
359 }
360 
361 static Attr *ProcessStmtAttribute(Sema &S, Stmt *St, const ParsedAttr &A,
362                                   SourceRange Range) {
363   switch (A.getKind()) {
364   case ParsedAttr::UnknownAttribute:
365     S.Diag(A.getLoc(), A.isDeclspecAttribute()
366                            ? (unsigned)diag::warn_unhandled_ms_attribute_ignored
367                            : (unsigned)diag::warn_unknown_attribute_ignored)
368         << A;
369     return nullptr;
370   case ParsedAttr::AT_FallThrough:
371     return handleFallThroughAttr(S, St, A, Range);
372   case ParsedAttr::AT_LoopHint:
373     return handleLoopHintAttr(S, St, A, Range);
374   case ParsedAttr::AT_OpenCLUnrollHint:
375     return handleOpenCLUnrollHint(S, St, A, Range);
376   case ParsedAttr::AT_Suppress:
377     return handleSuppressAttr(S, St, A, Range);
378   case ParsedAttr::AT_NoMerge:
379     return handleNoMergeAttr(S, St, A, Range);
380   default:
381     // if we're here, then we parsed a known attribute, but didn't recognize
382     // it as a statement attribute => it is declaration attribute
383     S.Diag(A.getRange().getBegin(), diag::err_decl_attribute_invalid_on_stmt)
384         << A << St->getBeginLoc();
385     return nullptr;
386   }
387 }
388 
389 StmtResult Sema::ProcessStmtAttributes(Stmt *S,
390                                        const ParsedAttributesView &AttrList,
391                                        SourceRange Range) {
392   SmallVector<const Attr*, 8> Attrs;
393   for (const ParsedAttr &AL : AttrList) {
394     if (Attr *a = ProcessStmtAttribute(*this, S, AL, Range))
395       Attrs.push_back(a);
396   }
397 
398   CheckForIncompatibleAttributes(*this, Attrs);
399 
400   if (Attrs.empty())
401     return S;
402 
403   return ActOnAttributedStmt(Range.getBegin(), Attrs, S);
404 }
405