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