1 //===--- SemaStmtAttr.cpp - Statement Attribute Handling ------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This file implements stmt-related attribute processing.
11 //
12 //===----------------------------------------------------------------------===//
13 
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/LoopHint.h"
20 #include "clang/Sema/ScopeInfo.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 AttributeList &A,
27                                    SourceRange Range) {
28   FallThroughAttr Attr(A.getRange(), S.Context,
29                        A.getAttributeSpellingListIndex());
30   if (!isa<NullStmt>(St)) {
31     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_wrong_target)
32         << Attr.getSpelling() << St->getLocStart();
33     if (isa<SwitchCase>(St)) {
34       SourceLocation L = S.getLocForEndOfToken(Range.getEnd());
35       S.Diag(L, diag::note_fallthrough_insert_semi_fixit)
36           << FixItHint::CreateInsertion(L, ";");
37     }
38     return nullptr;
39   }
40   auto *FnScope = S.getCurFunction();
41   if (FnScope->SwitchStack.empty()) {
42     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_outside_switch);
43     return nullptr;
44   }
45 
46   // If this is spelled as the standard C++17 attribute, but not in C++17, warn
47   // about using it as an extension.
48   if (!S.getLangOpts().CPlusPlus17 && A.isCXX11Attribute() &&
49       !A.getScopeName())
50     S.Diag(A.getLoc(), diag::ext_cxx17_attr) << A.getName();
51 
52   FnScope->setHasFallthroughStmt();
53   return ::new (S.Context) auto(Attr);
54 }
55 
56 static Attr *handleSuppressAttr(Sema &S, Stmt *St, const AttributeList &A,
57                                 SourceRange Range) {
58   if (A.getNumArgs() < 1) {
59     S.Diag(A.getLoc(), diag::err_attribute_too_few_arguments)
60         << A.getName() << 1;
61     return nullptr;
62   }
63 
64   std::vector<StringRef> DiagnosticIdentifiers;
65   for (unsigned I = 0, E = A.getNumArgs(); I != E; ++I) {
66     StringRef RuleName;
67 
68     if (!S.checkStringLiteralArgumentAttr(A, I, RuleName, nullptr))
69       return nullptr;
70 
71     // FIXME: Warn if the rule name is unknown. This is tricky because only
72     // clang-tidy knows about available rules.
73     DiagnosticIdentifiers.push_back(RuleName);
74   }
75 
76   return ::new (S.Context) SuppressAttr(
77       A.getRange(), S.Context, DiagnosticIdentifiers.data(),
78       DiagnosticIdentifiers.size(), A.getAttributeSpellingListIndex());
79 }
80 
81 static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const AttributeList &A,
82                                 SourceRange) {
83   IdentifierLoc *PragmaNameLoc = A.getArgAsIdent(0);
84   IdentifierLoc *OptionLoc = A.getArgAsIdent(1);
85   IdentifierLoc *StateLoc = A.getArgAsIdent(2);
86   Expr *ValueExpr = A.getArgAsExpr(3);
87 
88   bool PragmaUnroll = PragmaNameLoc->Ident->getName() == "unroll";
89   bool PragmaNoUnroll = PragmaNameLoc->Ident->getName() == "nounroll";
90   if (St->getStmtClass() != Stmt::DoStmtClass &&
91       St->getStmtClass() != Stmt::ForStmtClass &&
92       St->getStmtClass() != Stmt::CXXForRangeStmtClass &&
93       St->getStmtClass() != Stmt::WhileStmtClass) {
94     const char *Pragma =
95         llvm::StringSwitch<const char *>(PragmaNameLoc->Ident->getName())
96             .Case("unroll", "#pragma unroll")
97             .Case("nounroll", "#pragma nounroll")
98             .Default("#pragma clang loop");
99     S.Diag(St->getLocStart(), diag::err_pragma_loop_precedes_nonloop) << Pragma;
100     return nullptr;
101   }
102 
103   LoopHintAttr::Spelling Spelling =
104       LoopHintAttr::Spelling(A.getAttributeSpellingListIndex());
105   LoopHintAttr::OptionType Option;
106   LoopHintAttr::LoopHintState State;
107   if (PragmaNoUnroll) {
108     // #pragma nounroll
109     Option = LoopHintAttr::Unroll;
110     State = LoopHintAttr::Disable;
111   } else if (PragmaUnroll) {
112     if (ValueExpr) {
113       // #pragma unroll N
114       Option = LoopHintAttr::UnrollCount;
115       State = LoopHintAttr::Numeric;
116     } else {
117       // #pragma unroll
118       Option = LoopHintAttr::Unroll;
119       State = LoopHintAttr::Enable;
120     }
121   } else {
122     // #pragma clang loop ...
123     assert(OptionLoc && OptionLoc->Ident &&
124            "Attribute must have valid option info.");
125     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
126                  OptionLoc->Ident->getName())
127                  .Case("vectorize", LoopHintAttr::Vectorize)
128                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
129                  .Case("interleave", LoopHintAttr::Interleave)
130                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
131                  .Case("unroll", LoopHintAttr::Unroll)
132                  .Case("unroll_count", LoopHintAttr::UnrollCount)
133                  .Case("distribute", LoopHintAttr::Distribute)
134                  .Default(LoopHintAttr::Vectorize);
135     if (Option == LoopHintAttr::VectorizeWidth ||
136         Option == LoopHintAttr::InterleaveCount ||
137         Option == LoopHintAttr::UnrollCount) {
138       assert(ValueExpr && "Attribute must have a valid value expression.");
139       if (S.CheckLoopHintExpr(ValueExpr, St->getLocStart()))
140         return nullptr;
141       State = LoopHintAttr::Numeric;
142     } else if (Option == LoopHintAttr::Vectorize ||
143                Option == LoopHintAttr::Interleave ||
144                Option == LoopHintAttr::Unroll ||
145                Option == LoopHintAttr::Distribute) {
146       assert(StateLoc && StateLoc->Ident && "Loop hint must have an argument");
147       if (StateLoc->Ident->isStr("disable"))
148         State = LoopHintAttr::Disable;
149       else if (StateLoc->Ident->isStr("assume_safety"))
150         State = LoopHintAttr::AssumeSafety;
151       else if (StateLoc->Ident->isStr("full"))
152         State = LoopHintAttr::Full;
153       else if (StateLoc->Ident->isStr("enable"))
154         State = LoopHintAttr::Enable;
155       else
156         llvm_unreachable("bad loop hint argument");
157     } else
158       llvm_unreachable("bad loop hint");
159   }
160 
161   return LoopHintAttr::CreateImplicit(S.Context, Spelling, Option, State,
162                                       ValueExpr, A.getRange());
163 }
164 
165 static void
166 CheckForIncompatibleAttributes(Sema &S,
167                                const SmallVectorImpl<const Attr *> &Attrs) {
168   // There are 4 categories of loop hints attributes: vectorize, interleave,
169   // unroll and distribute. Except for distribute they come in two variants: a
170   // state form and a numeric form.  The state form selectively
171   // defaults/enables/disables the transformation for the loop (for unroll,
172   // default indicates full unrolling rather than enabling the transformation).
173   // The numeric form form provides an integer hint (for example, unroll count)
174   // to the transformer. The following array accumulates the hints encountered
175   // while iterating through the attributes to check for compatibility.
176   struct {
177     const LoopHintAttr *StateAttr;
178     const LoopHintAttr *NumericAttr;
179   } HintAttrs[] = {{nullptr, nullptr},
180                    {nullptr, nullptr},
181                    {nullptr, nullptr},
182                    {nullptr, nullptr}};
183 
184   for (const auto *I : Attrs) {
185     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
186 
187     // Skip non loop hint attributes
188     if (!LH)
189       continue;
190 
191     LoopHintAttr::OptionType Option = LH->getOption();
192     enum { Vectorize, Interleave, Unroll, Distribute } Category;
193     switch (Option) {
194     case LoopHintAttr::Vectorize:
195     case LoopHintAttr::VectorizeWidth:
196       Category = Vectorize;
197       break;
198     case LoopHintAttr::Interleave:
199     case LoopHintAttr::InterleaveCount:
200       Category = Interleave;
201       break;
202     case LoopHintAttr::Unroll:
203     case LoopHintAttr::UnrollCount:
204       Category = Unroll;
205       break;
206     case LoopHintAttr::Distribute:
207       // Perform the check for duplicated 'distribute' hints.
208       Category = Distribute;
209       break;
210     };
211 
212     auto &CategoryState = HintAttrs[Category];
213     const LoopHintAttr *PrevAttr;
214     if (Option == LoopHintAttr::Vectorize ||
215         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
216         Option == LoopHintAttr::Distribute) {
217       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
218       PrevAttr = CategoryState.StateAttr;
219       CategoryState.StateAttr = LH;
220     } else {
221       // Numeric hint.  For example, vectorize_width(8).
222       PrevAttr = CategoryState.NumericAttr;
223       CategoryState.NumericAttr = LH;
224     }
225 
226     PrintingPolicy Policy(S.Context.getLangOpts());
227     SourceLocation OptionLoc = LH->getRange().getBegin();
228     if (PrevAttr)
229       // Cannot specify same type of attribute twice.
230       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
231           << /*Duplicate=*/true << PrevAttr->getDiagnosticName(Policy)
232           << LH->getDiagnosticName(Policy);
233 
234     if (CategoryState.StateAttr && CategoryState.NumericAttr &&
235         (Category == Unroll ||
236          CategoryState.StateAttr->getState() == LoopHintAttr::Disable)) {
237       // Disable hints are not compatible with numeric hints of the same
238       // category.  As a special case, numeric unroll hints are also not
239       // compatible with enable or full form of the unroll pragma because these
240       // directives indicate full unrolling.
241       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
242           << /*Duplicate=*/false
243           << CategoryState.StateAttr->getDiagnosticName(Policy)
244           << CategoryState.NumericAttr->getDiagnosticName(Policy);
245     }
246   }
247 }
248 
249 static Attr *handleOpenCLUnrollHint(Sema &S, Stmt *St, const AttributeList &A,
250                                     SourceRange Range) {
251   // Although the feature was introduced only in OpenCL C v2.0 s6.11.5, it's
252   // useful for OpenCL 1.x too and doesn't require HW support.
253   // opencl_unroll_hint can have 0 arguments (compiler
254   // determines unrolling factor) or 1 argument (the unroll factor provided
255   // by the user).
256 
257   unsigned NumArgs = A.getNumArgs();
258 
259   if (NumArgs > 1) {
260     S.Diag(A.getLoc(), diag::err_attribute_too_many_arguments) << A.getName()
261                                                                << 1;
262     return nullptr;
263   }
264 
265   unsigned UnrollFactor = 0;
266 
267   if (NumArgs == 1) {
268     Expr *E = A.getArgAsExpr(0);
269     llvm::APSInt ArgVal(32);
270 
271     if (!E->isIntegerConstantExpr(ArgVal, S.Context)) {
272       S.Diag(A.getLoc(), diag::err_attribute_argument_type)
273           << A.getName() << AANT_ArgumentIntegerConstant << E->getSourceRange();
274       return nullptr;
275     }
276 
277     int Val = ArgVal.getSExtValue();
278 
279     if (Val <= 0) {
280       S.Diag(A.getRange().getBegin(),
281              diag::err_attribute_requires_positive_integer)
282           << A.getName();
283       return nullptr;
284     }
285     UnrollFactor = Val;
286   }
287 
288   return OpenCLUnrollHintAttr::CreateImplicit(S.Context, UnrollFactor);
289 }
290 
291 static Attr *ProcessStmtAttribute(Sema &S, Stmt *St, const AttributeList &A,
292                                   SourceRange Range) {
293   switch (A.getKind()) {
294   case AttributeList::UnknownAttribute:
295     S.Diag(A.getLoc(), A.isDeclspecAttribute() ?
296            diag::warn_unhandled_ms_attribute_ignored :
297            diag::warn_unknown_attribute_ignored) << A.getName();
298     return nullptr;
299   case AttributeList::AT_FallThrough:
300     return handleFallThroughAttr(S, St, A, Range);
301   case AttributeList::AT_LoopHint:
302     return handleLoopHintAttr(S, St, A, Range);
303   case AttributeList::AT_OpenCLUnrollHint:
304     return handleOpenCLUnrollHint(S, St, A, Range);
305   case AttributeList::AT_Suppress:
306     return handleSuppressAttr(S, St, A, Range);
307   default:
308     // if we're here, then we parsed a known attribute, but didn't recognize
309     // it as a statement attribute => it is declaration attribute
310     S.Diag(A.getRange().getBegin(), diag::err_decl_attribute_invalid_on_stmt)
311         << A.getName() << St->getLocStart();
312     return nullptr;
313   }
314 }
315 
316 StmtResult Sema::ProcessStmtAttributes(Stmt *S, AttributeList *AttrList,
317                                        SourceRange Range) {
318   SmallVector<const Attr*, 8> Attrs;
319   for (const AttributeList* l = AttrList; l; l = l->getNext()) {
320     if (Attr *a = ProcessStmtAttribute(*this, S, *l, Range))
321       Attrs.push_back(a);
322   }
323 
324   CheckForIncompatibleAttributes(*this, Attrs);
325 
326   if (Attrs.empty())
327     return S;
328 
329   return ActOnAttributedStmt(Range.getBegin(), Attrs, S);
330 }
331