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/ASTContext.h"
14 #include "clang/AST/EvaluatedExprVisitor.h"
15 #include "clang/Basic/SourceManager.h"
16 #include "clang/Basic/TargetInfo.h"
17 #include "clang/Sema/DelayedDiagnostic.h"
18 #include "clang/Sema/Lookup.h"
19 #include "clang/Sema/ScopeInfo.h"
20 #include "clang/Sema/SemaInternal.h"
21 #include "llvm/ADT/StringExtras.h"
22 
23 using namespace clang;
24 using namespace sema;
25 
26 static Attr *handleFallThroughAttr(Sema &S, Stmt *St, const ParsedAttr &A,
27                                    SourceRange Range) {
28   FallThroughAttr Attr(S.Context, A);
29   if (isa<SwitchCase>(St)) {
30     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_wrong_target)
31         << A << St->getBeginLoc();
32     SourceLocation L = S.getLocForEndOfToken(Range.getEnd());
33     S.Diag(L, diag::note_fallthrough_insert_semi_fixit)
34         << FixItHint::CreateInsertion(L, ";");
35     return nullptr;
36   }
37   auto *FnScope = S.getCurFunction();
38   if (FnScope->SwitchStack.empty()) {
39     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_outside_switch);
40     return nullptr;
41   }
42 
43   // If this is spelled as the standard C++17 attribute, but not in C++17, warn
44   // about using it as an extension.
45   if (!S.getLangOpts().CPlusPlus17 && A.isCXX11Attribute() &&
46       !A.getScopeName())
47     S.Diag(A.getLoc(), diag::ext_cxx17_attr) << A;
48 
49   FnScope->setHasFallthroughStmt();
50   return ::new (S.Context) FallThroughAttr(S.Context, A);
51 }
52 
53 static Attr *handleSuppressAttr(Sema &S, Stmt *St, const ParsedAttr &A,
54                                 SourceRange Range) {
55   std::vector<StringRef> DiagnosticIdentifiers;
56   for (unsigned I = 0, E = A.getNumArgs(); I != E; ++I) {
57     StringRef RuleName;
58 
59     if (!S.checkStringLiteralArgumentAttr(A, I, RuleName, nullptr))
60       return nullptr;
61 
62     // FIXME: Warn if the rule name is unknown. This is tricky because only
63     // clang-tidy knows about available rules.
64     DiagnosticIdentifiers.push_back(RuleName);
65   }
66 
67   return ::new (S.Context) SuppressAttr(
68       S.Context, A, DiagnosticIdentifiers.data(), DiagnosticIdentifiers.size());
69 }
70 
71 static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
72                                 SourceRange) {
73   IdentifierLoc *PragmaNameLoc = A.getArgAsIdent(0);
74   IdentifierLoc *OptionLoc = A.getArgAsIdent(1);
75   IdentifierLoc *StateLoc = A.getArgAsIdent(2);
76   Expr *ValueExpr = A.getArgAsExpr(3);
77 
78   StringRef PragmaName =
79       llvm::StringSwitch<StringRef>(PragmaNameLoc->Ident->getName())
80           .Cases("unroll", "nounroll", "unroll_and_jam", "nounroll_and_jam",
81                  PragmaNameLoc->Ident->getName())
82           .Default("clang loop");
83 
84   // This could be handled automatically by adding a Subjects definition in
85   // Attr.td, but that would make the diagnostic behavior worse in this case
86   // because the user spells this attribute as a pragma.
87   if (!isa<DoStmt, ForStmt, CXXForRangeStmt, WhileStmt>(St)) {
88     std::string Pragma = "#pragma " + std::string(PragmaName);
89     S.Diag(St->getBeginLoc(), diag::err_pragma_loop_precedes_nonloop) << Pragma;
90     return nullptr;
91   }
92 
93   LoopHintAttr::OptionType Option;
94   LoopHintAttr::LoopHintState State;
95 
96   auto SetHints = [&Option, &State](LoopHintAttr::OptionType O,
97                                     LoopHintAttr::LoopHintState S) {
98     Option = O;
99     State = S;
100   };
101 
102   if (PragmaName == "nounroll") {
103     SetHints(LoopHintAttr::Unroll, LoopHintAttr::Disable);
104   } else if (PragmaName == "unroll") {
105     // #pragma unroll N
106     if (ValueExpr)
107       SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Numeric);
108     else
109       SetHints(LoopHintAttr::Unroll, LoopHintAttr::Enable);
110   } else if (PragmaName == "nounroll_and_jam") {
111     SetHints(LoopHintAttr::UnrollAndJam, LoopHintAttr::Disable);
112   } else if (PragmaName == "unroll_and_jam") {
113     // #pragma unroll_and_jam N
114     if (ValueExpr)
115       SetHints(LoopHintAttr::UnrollAndJamCount, LoopHintAttr::Numeric);
116     else
117       SetHints(LoopHintAttr::UnrollAndJam, LoopHintAttr::Enable);
118   } else {
119     // #pragma clang loop ...
120     assert(OptionLoc && OptionLoc->Ident &&
121            "Attribute must have valid option info.");
122     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
123                  OptionLoc->Ident->getName())
124                  .Case("vectorize", LoopHintAttr::Vectorize)
125                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
126                  .Case("interleave", LoopHintAttr::Interleave)
127                  .Case("vectorize_predicate", LoopHintAttr::VectorizePredicate)
128                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
129                  .Case("unroll", LoopHintAttr::Unroll)
130                  .Case("unroll_count", LoopHintAttr::UnrollCount)
131                  .Case("pipeline", LoopHintAttr::PipelineDisabled)
132                  .Case("pipeline_initiation_interval",
133                        LoopHintAttr::PipelineInitiationInterval)
134                  .Case("distribute", LoopHintAttr::Distribute)
135                  .Default(LoopHintAttr::Vectorize);
136     if (Option == LoopHintAttr::VectorizeWidth) {
137       assert((ValueExpr || (StateLoc && StateLoc->Ident)) &&
138              "Attribute must have a valid value expression or argument.");
139       if (ValueExpr && S.CheckLoopHintExpr(ValueExpr, St->getBeginLoc()))
140         return nullptr;
141       if (StateLoc && StateLoc->Ident && StateLoc->Ident->isStr("scalable"))
142         State = LoopHintAttr::ScalableWidth;
143       else
144         State = LoopHintAttr::FixedWidth;
145     } else if (Option == LoopHintAttr::InterleaveCount ||
146                Option == LoopHintAttr::UnrollCount ||
147                Option == LoopHintAttr::PipelineInitiationInterval) {
148       assert(ValueExpr && "Attribute must have a valid value expression.");
149       if (S.CheckLoopHintExpr(ValueExpr, St->getBeginLoc()))
150         return nullptr;
151       State = LoopHintAttr::Numeric;
152     } else if (Option == LoopHintAttr::Vectorize ||
153                Option == LoopHintAttr::Interleave ||
154                Option == LoopHintAttr::VectorizePredicate ||
155                Option == LoopHintAttr::Unroll ||
156                Option == LoopHintAttr::Distribute ||
157                Option == LoopHintAttr::PipelineDisabled) {
158       assert(StateLoc && StateLoc->Ident && "Loop hint must have an argument");
159       if (StateLoc->Ident->isStr("disable"))
160         State = LoopHintAttr::Disable;
161       else if (StateLoc->Ident->isStr("assume_safety"))
162         State = LoopHintAttr::AssumeSafety;
163       else if (StateLoc->Ident->isStr("full"))
164         State = LoopHintAttr::Full;
165       else if (StateLoc->Ident->isStr("enable"))
166         State = LoopHintAttr::Enable;
167       else
168         llvm_unreachable("bad loop hint argument");
169     } else
170       llvm_unreachable("bad loop hint");
171   }
172 
173   return LoopHintAttr::CreateImplicit(S.Context, Option, State, ValueExpr, A);
174 }
175 
176 namespace {
177 class CallExprFinder : public ConstEvaluatedExprVisitor<CallExprFinder> {
178   bool FoundCallExpr = false;
179 
180 public:
181   typedef ConstEvaluatedExprVisitor<CallExprFinder> Inherited;
182 
183   CallExprFinder(Sema &S, const Stmt *St) : Inherited(S.Context) { Visit(St); }
184 
185   bool foundCallExpr() { return FoundCallExpr; }
186 
187   void VisitCallExpr(const CallExpr *E) { FoundCallExpr = true; }
188   void VisitAsmStmt(const AsmStmt *S) { FoundCallExpr = true; }
189 
190   void Visit(const Stmt *St) {
191     if (!St)
192       return;
193     ConstEvaluatedExprVisitor<CallExprFinder>::Visit(St);
194   }
195 };
196 } // namespace
197 
198 static Attr *handleNoMergeAttr(Sema &S, Stmt *St, const ParsedAttr &A,
199                                SourceRange Range) {
200   NoMergeAttr NMA(S.Context, A);
201   CallExprFinder CEF(S, St);
202 
203   if (!CEF.foundCallExpr()) {
204     S.Diag(St->getBeginLoc(), diag::warn_nomerge_attribute_ignored_in_stmt)
205         << NMA.getSpelling();
206     return nullptr;
207   }
208 
209   return ::new (S.Context) NoMergeAttr(S.Context, A);
210 }
211 
212 static Attr *handleLikely(Sema &S, Stmt *St, const ParsedAttr &A,
213                           SourceRange Range) {
214 
215   if (!S.getLangOpts().CPlusPlus20 && A.isCXX11Attribute() && !A.getScopeName())
216     S.Diag(A.getLoc(), diag::ext_cxx20_attr) << A << Range;
217 
218   return ::new (S.Context) LikelyAttr(S.Context, A);
219 }
220 
221 static Attr *handleUnlikely(Sema &S, Stmt *St, const ParsedAttr &A,
222                             SourceRange Range) {
223 
224   if (!S.getLangOpts().CPlusPlus20 && A.isCXX11Attribute() && !A.getScopeName())
225     S.Diag(A.getLoc(), diag::ext_cxx20_attr) << A << Range;
226 
227   return ::new (S.Context) UnlikelyAttr(S.Context, A);
228 }
229 
230 #define WANT_STMT_MERGE_LOGIC
231 #include "clang/Sema/AttrParsedAttrImpl.inc"
232 #undef WANT_STMT_MERGE_LOGIC
233 
234 static void
235 CheckForIncompatibleAttributes(Sema &S,
236                                const SmallVectorImpl<const Attr *> &Attrs) {
237   // The vast majority of attributed statements will only have one attribute
238   // on them, so skip all of the checking in the common case.
239   if (Attrs.size() < 2)
240     return;
241 
242   // First, check for the easy cases that are table-generated for us.
243   if (!DiagnoseMutualExclusions(S, Attrs))
244     return;
245 
246   // There are 6 categories of loop hints attributes: vectorize, interleave,
247   // unroll, unroll_and_jam, pipeline and distribute. Except for distribute they
248   // come in two variants: a state form and a numeric form.  The state form
249   // selectively defaults/enables/disables the transformation for the loop
250   // (for unroll, default indicates full unrolling rather than enabling the
251   // transformation). The numeric form form provides an integer hint (for
252   // example, unroll count) to the transformer. The following array accumulates
253   // the hints encountered while iterating through the attributes to check for
254   // compatibility.
255   struct {
256     const LoopHintAttr *StateAttr;
257     const LoopHintAttr *NumericAttr;
258   } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
259                    {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
260                    {nullptr, nullptr}};
261 
262   for (const auto *I : Attrs) {
263     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
264 
265     // Skip non loop hint attributes
266     if (!LH)
267       continue;
268 
269     LoopHintAttr::OptionType Option = LH->getOption();
270     enum {
271       Vectorize,
272       Interleave,
273       Unroll,
274       UnrollAndJam,
275       Distribute,
276       Pipeline,
277       VectorizePredicate
278     } Category;
279     switch (Option) {
280     case LoopHintAttr::Vectorize:
281     case LoopHintAttr::VectorizeWidth:
282       Category = Vectorize;
283       break;
284     case LoopHintAttr::Interleave:
285     case LoopHintAttr::InterleaveCount:
286       Category = Interleave;
287       break;
288     case LoopHintAttr::Unroll:
289     case LoopHintAttr::UnrollCount:
290       Category = Unroll;
291       break;
292     case LoopHintAttr::UnrollAndJam:
293     case LoopHintAttr::UnrollAndJamCount:
294       Category = UnrollAndJam;
295       break;
296     case LoopHintAttr::Distribute:
297       // Perform the check for duplicated 'distribute' hints.
298       Category = Distribute;
299       break;
300     case LoopHintAttr::PipelineDisabled:
301     case LoopHintAttr::PipelineInitiationInterval:
302       Category = Pipeline;
303       break;
304     case LoopHintAttr::VectorizePredicate:
305       Category = VectorizePredicate;
306       break;
307     };
308 
309     assert(Category < sizeof(HintAttrs) / sizeof(HintAttrs[0]));
310     auto &CategoryState = HintAttrs[Category];
311     const LoopHintAttr *PrevAttr;
312     if (Option == LoopHintAttr::Vectorize ||
313         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
314         Option == LoopHintAttr::UnrollAndJam ||
315         Option == LoopHintAttr::VectorizePredicate ||
316         Option == LoopHintAttr::PipelineDisabled ||
317         Option == LoopHintAttr::Distribute) {
318       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
319       PrevAttr = CategoryState.StateAttr;
320       CategoryState.StateAttr = LH;
321     } else {
322       // Numeric hint.  For example, vectorize_width(8).
323       PrevAttr = CategoryState.NumericAttr;
324       CategoryState.NumericAttr = LH;
325     }
326 
327     PrintingPolicy Policy(S.Context.getLangOpts());
328     SourceLocation OptionLoc = LH->getRange().getBegin();
329     if (PrevAttr)
330       // Cannot specify same type of attribute twice.
331       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
332           << /*Duplicate=*/true << PrevAttr->getDiagnosticName(Policy)
333           << LH->getDiagnosticName(Policy);
334 
335     if (CategoryState.StateAttr && CategoryState.NumericAttr &&
336         (Category == Unroll || Category == UnrollAndJam ||
337          CategoryState.StateAttr->getState() == LoopHintAttr::Disable)) {
338       // Disable hints are not compatible with numeric hints of the same
339       // category.  As a special case, numeric unroll hints are also not
340       // compatible with enable or full form of the unroll pragma because these
341       // directives indicate full unrolling.
342       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
343           << /*Duplicate=*/false
344           << CategoryState.StateAttr->getDiagnosticName(Policy)
345           << CategoryState.NumericAttr->getDiagnosticName(Policy);
346     }
347   }
348 }
349 
350 static Attr *handleOpenCLUnrollHint(Sema &S, Stmt *St, const ParsedAttr &A,
351                                     SourceRange Range) {
352   // Although the feature was introduced only in OpenCL C v2.0 s6.11.5, it's
353   // useful for OpenCL 1.x too and doesn't require HW support.
354   // opencl_unroll_hint can have 0 arguments (compiler
355   // determines unrolling factor) or 1 argument (the unroll factor provided
356   // by the user).
357   unsigned UnrollFactor = 0;
358   if (A.getNumArgs() == 1) {
359     Expr *E = A.getArgAsExpr(0);
360     Optional<llvm::APSInt> ArgVal;
361 
362     if (!(ArgVal = E->getIntegerConstantExpr(S.Context))) {
363       S.Diag(A.getLoc(), diag::err_attribute_argument_type)
364           << A << AANT_ArgumentIntegerConstant << E->getSourceRange();
365       return nullptr;
366     }
367 
368     int Val = ArgVal->getSExtValue();
369     if (Val <= 0) {
370       S.Diag(A.getRange().getBegin(),
371              diag::err_attribute_requires_positive_integer)
372           << A << /* positive */ 0;
373       return nullptr;
374     }
375     UnrollFactor = static_cast<unsigned>(Val);
376   }
377 
378   return ::new (S.Context) OpenCLUnrollHintAttr(S.Context, A, UnrollFactor);
379 }
380 
381 static Attr *ProcessStmtAttribute(Sema &S, Stmt *St, const ParsedAttr &A,
382                                   SourceRange Range) {
383   if (A.isInvalid() || A.getKind() == ParsedAttr::IgnoredAttribute)
384     return nullptr;
385 
386   // Unknown attributes are automatically warned on. Target-specific attributes
387   // which do not apply to the current target architecture are treated as
388   // though they were unknown attributes.
389   const TargetInfo *Aux = S.Context.getAuxTargetInfo();
390   if (A.getKind() == ParsedAttr::UnknownAttribute ||
391       !(A.existsInTarget(S.Context.getTargetInfo()) ||
392         (S.Context.getLangOpts().SYCLIsDevice && Aux &&
393          A.existsInTarget(*Aux)))) {
394     S.Diag(A.getLoc(), A.isDeclspecAttribute()
395                            ? (unsigned)diag::warn_unhandled_ms_attribute_ignored
396                            : (unsigned)diag::warn_unknown_attribute_ignored)
397         << A << A.getRange();
398     return nullptr;
399   }
400 
401   if (S.checkCommonAttributeFeatures(St, A))
402     return nullptr;
403 
404   switch (A.getKind()) {
405   case ParsedAttr::AT_FallThrough:
406     return handleFallThroughAttr(S, St, A, Range);
407   case ParsedAttr::AT_LoopHint:
408     return handleLoopHintAttr(S, St, A, Range);
409   case ParsedAttr::AT_OpenCLUnrollHint:
410     return handleOpenCLUnrollHint(S, St, A, Range);
411   case ParsedAttr::AT_Suppress:
412     return handleSuppressAttr(S, St, A, Range);
413   case ParsedAttr::AT_NoMerge:
414     return handleNoMergeAttr(S, St, A, Range);
415   case ParsedAttr::AT_Likely:
416     return handleLikely(S, St, A, Range);
417   case ParsedAttr::AT_Unlikely:
418     return handleUnlikely(S, St, A, Range);
419   default:
420     // N.B., ClangAttrEmitter.cpp emits a diagnostic helper that ensures a
421     // declaration attribute is not written on a statement, but this code is
422     // needed for attributes in Attr.td that do not list any subjects.
423     S.Diag(A.getRange().getBegin(), diag::err_decl_attribute_invalid_on_stmt)
424         << A << St->getBeginLoc();
425     return nullptr;
426   }
427 }
428 
429 void Sema::ProcessStmtAttributes(Stmt *S,
430                                  const ParsedAttributesWithRange &InAttrs,
431                                  SmallVectorImpl<const Attr *> &OutAttrs) {
432   for (const ParsedAttr &AL : InAttrs) {
433     if (const Attr *A = ProcessStmtAttribute(*this, S, AL, InAttrs.Range))
434       OutAttrs.push_back(A);
435   }
436 
437   CheckForIncompatibleAttributes(*this, OutAttrs);
438 }
439