1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

#ifndef LO_CLANG_SHARED_PLUGINS

#include <algorithm>
#include <cassert>
#include <map>

#include "check.hxx"
#include "compat.hxx"
#include "plugin.hxx"

// Find cases where a variable of a string type (at least for now, only OUString) is initialized
// with a literal value (incl. as an empty string) and used only once.  Conservatively this only
// covers local non-static variables that are not defined outside of the loop (if any) in which they
// are used, as other cases may deliberately use the variable for performance (or even correctness,
// if addresses are taken and compared) reasons.
//
// For one, the historically heavy syntax for such uses of string literals
// (RTL_CONSTASCII_USTRINGPARAM etc.) probably explains many of these redundant variables, wich can
// now be considered cargo-cult baggage.  For another, some of those variables are used as arguments
// to functions which also have more efficient overloads directly taking string literals.  And for
// yet another, some cases with default-initialized variables turned out to be effectively unused
// code that could be removed completely (d073cca5f7c04de3e1bcedda334d864e98ac7835 "Clean up dead
// code", 91345e7dde6100496a7c9e815b72b2821ae82bc2 "Clean up dead code",
// 868b0763ac47f765cb48c277897274a595b831d0 "Upcoming loplugin:elidestringvar: dbaccess" in
// dbaccess/source/ui/app/AppController.cxx, bde0aac4ccf7b830b5ef21d5b9e75e62aee6aaf9 "Clean up dead
// code", 354aefec42de856b4ab6201ada54a3a3c630b4bd "Upcoming loplugin:elidestringvar: cui" in
// cui/source/dialogs/SpellDialog.cxx).

namespace
{
class ElideStringVar : public loplugin::FilteringPlugin<ElideStringVar>
{
public:
    explicit ElideStringVar(loplugin::InstantiationData const& data)
        : FilteringPlugin(data)
    {
    }

    bool preRun() override { return compiler.getLangOpts().CPlusPlus; }

    void postRun() override
    {
        for (auto const& var : vars_)
        {
            if (!var.second.singleUse || *var.second.singleUse == nullptr)
            {
                continue;
            }
            if (containsPreprocessingConditionalInclusion(SourceRange(
                    compat::getBeginLoc(var.first), compat::getEndLoc(*var.second.singleUse))))
            {
                // This is not perfect, as additional uses can be hidden in conditional blocks that
                // only start after the (would-be) single use (as was the case in
                // 3bc5057f9689e024957cfa898a221ee2c4c4afe7 "Upcoming loplugin:elidestringvar:
                // testtools" when built with --enable-debug, but where also fixing the hidden
                // additional use was trivial).  If this ever becomes a real problem, we can extend
                // the above check to cover more of the current function body's remainder.
                continue;
            }
            report(DiagnosticsEngine::Warning,
                   "replace single use of literal OUString variable with the literal",
                   (*var.second.singleUse)->getExprLoc())
                << (*var.second.singleUse)->getSourceRange();
            report(DiagnosticsEngine::Note, "literal OUString variable defined here",
                   var.first->getLocation())
                << var.first->getSourceRange();
        }
    }

    bool VisitVarDecl(VarDecl const* decl)
    {
        if (ignoreLocation(decl))
        {
            return true;
        }
        if (!decl->isThisDeclarationADefinition())
        {
            return true;
        }
        if (isa<ParmVarDecl>(decl))
        {
            return true;
        }
        if (decl->getStorageDuration() != SD_Automatic)
        {
            return true;
        }
        if (!loplugin::TypeCheck(decl->getType())
                 .Class("OUString")
                 .Namespace("rtl")
                 .GlobalNamespace())
        {
            return true;
        }
        if (!decl->hasInit())
        {
            return true;
        }
        auto const e1 = dyn_cast<CXXConstructExpr>(decl->getInit()->IgnoreParenImpCasts());
        if (e1 == nullptr)
        {
            return true;
        }
        if (!loplugin::TypeCheck(e1->getType())
                 .Class("OUString")
                 .Namespace("rtl")
                 .GlobalNamespace())
        {
            return true;
        }
        switch (e1->getNumArgs())
        {
            case 0:
                break;
            case 2:
            {
                auto const e2 = e1->getArg(1);
                if (!(isa<CXXDefaultArgExpr>(e2)
                      && loplugin::TypeCheck(e2->getType())
                             .Struct("Dummy")
                             .Namespace("libreoffice_internal")
                             .Namespace("rtl")
                             .GlobalNamespace()))
                {
                    return true;
                }
                break;
            }
            default:
                return true;
        }
        auto const ok = vars_.emplace(decl, Data(getInnermostLoop()));
        assert(ok.second);
        (void)ok;
        return true;
    }

    bool VisitDeclRefExpr(DeclRefExpr const* expr)
    {
        if (ignoreLocation(expr))
        {
            return true;
        }
        auto const var = dyn_cast<VarDecl>(expr->getDecl());
        if (var == nullptr)
        {
            return true;
        }
        auto const i = vars_.find(var);
        if (i == vars_.end())
        {
            return true;
        }
        i->second.singleUse
            = i->second.singleUse || i->second.innermostLoop != getInnermostLoop() ? nullptr : expr;
        return true;
    }

    bool VisitMemberExpr(MemberExpr const* expr)
    {
        if (ignoreLocation(expr))
        {
            return true;
        }
        auto const e = dyn_cast<DeclRefExpr>(expr->getBase()->IgnoreParenImpCasts());
        if (e == nullptr)
        {
            return true;
        }
        auto const var = dyn_cast<VarDecl>(e->getDecl());
        if (var == nullptr)
        {
            return true;
        }
        auto const i = vars_.find(var);
        if (i == vars_.end())
        {
            return true;
        }
        i->second.singleUse = nullptr;
        return true;
    }

    bool VisitUnaryOperator(UnaryOperator const* expr)
    {
        if (ignoreLocation(expr))
        {
            return true;
        }
        if (expr->getOpcode() != UO_AddrOf)
        {
            return true;
        }
        auto const e = dyn_cast<DeclRefExpr>(expr->getSubExpr()->IgnoreParenImpCasts());
        if (e == nullptr)
        {
            return true;
        }
        auto const var = dyn_cast<VarDecl>(e->getDecl());
        if (var == nullptr)
        {
            return true;
        }
        auto const i = vars_.find(var);
        if (i == vars_.end())
        {
            return true;
        }
        i->second.singleUse = nullptr;
        return true;
    }

    bool VisitCallExpr(CallExpr const* expr)
    {
        if (ignoreLocation(expr))
        {
            return true;
        }
        auto const fun = expr->getDirectCallee();
        if (fun == nullptr)
        {
            return true;
        }
        unsigned const n = std::min(fun->getNumParams(), expr->getNumArgs());
        for (unsigned i = 0; i != n; ++i)
        {
            if (!loplugin::TypeCheck(fun->getParamDecl(i)->getType())
                     .LvalueReference()
                     .NonConstVolatile())
            {
                continue;
            }
            auto const e = dyn_cast<DeclRefExpr>(expr->getArg(i)->IgnoreParenImpCasts());
            if (e == nullptr)
            {
                continue;
            }
            auto const var = dyn_cast<VarDecl>(e->getDecl());
            if (var == nullptr)
            {
                continue;
            }
            auto const j = vars_.find(var);
            if (j == vars_.end())
            {
                continue;
            }
            j->second.singleUse = nullptr;
        }
        return true;
    }

    bool VisitCXXConstructExpr(CXXConstructExpr const* expr)
    {
        if (ignoreLocation(expr))
        {
            return true;
        }
        auto const ctor = expr->getConstructor();
        unsigned const n = std::min(ctor->getNumParams(), expr->getNumArgs());
        for (unsigned i = 0; i != n; ++i)
        {
            if (!loplugin::TypeCheck(ctor->getParamDecl(i)->getType())
                     .LvalueReference()
                     .NonConstVolatile())
            {
                continue;
            }
            auto const e = dyn_cast<DeclRefExpr>(expr->getArg(i)->IgnoreParenImpCasts());
            if (e == nullptr)
            {
                continue;
            }
            auto const var = dyn_cast<VarDecl>(e->getDecl());
            if (var == nullptr)
            {
                continue;
            }
            auto const j = vars_.find(var);
            if (j == vars_.end())
            {
                continue;
            }
            j->second.singleUse = nullptr;
        }
        return true;
    }

    bool TraverseWhileStmt(WhileStmt* stmt)
    {
        bool ret = true;
        if (PreTraverseWhileStmt(stmt))
        {
            ret = FilteringPlugin::TraverseWhileStmt(stmt);
            PostTraverseWhileStmt(stmt, ret);
        }
        return ret;
    }

    bool PreTraverseWhileStmt(WhileStmt* stmt)
    {
        innermostLoop_.push(stmt);
        return true;
    }

    bool PostTraverseWhileStmt(WhileStmt* stmt, bool)
    {
        assert(!innermostLoop_.empty());
        assert(innermostLoop_.top() == stmt);
        (void)stmt;
        innermostLoop_.pop();
        return true;
    }

    bool TraverseDoStmt(DoStmt* stmt)
    {
        bool ret = true;
        if (PreTraverseDoStmt(stmt))
        {
            ret = FilteringPlugin::TraverseDoStmt(stmt);
            PostTraverseDoStmt(stmt, ret);
        }
        return ret;
    }

    bool PreTraverseDoStmt(DoStmt* stmt)
    {
        innermostLoop_.push(stmt);
        return true;
    }

    bool PostTraverseDoStmt(DoStmt* stmt, bool)
    {
        assert(!innermostLoop_.empty());
        assert(innermostLoop_.top() == stmt);
        (void)stmt;
        innermostLoop_.pop();
        return true;
    }

    bool TraverseForStmt(ForStmt* stmt)
    {
        bool ret = true;
        if (PreTraverseForStmt(stmt))
        {
            ret = FilteringPlugin::TraverseForStmt(stmt);
            PostTraverseForStmt(stmt, ret);
        }
        return ret;
    }

    bool PreTraverseForStmt(ForStmt* stmt)
    {
        innermostLoop_.push(stmt);
        return true;
    }

    bool PostTraverseForStmt(ForStmt* stmt, bool)
    {
        assert(!innermostLoop_.empty());
        assert(innermostLoop_.top() == stmt);
        (void)stmt;
        innermostLoop_.pop();
        return true;
    }

    bool TraverseCXXForRangeStmt(CXXForRangeStmt* stmt)
    {
        bool ret = true;
        if (PreTraverseCXXForRangeStmt(stmt))
        {
            ret = FilteringPlugin::TraverseCXXForRangeStmt(stmt);
            PostTraverseCXXForRangeStmt(stmt, ret);
        }
        return ret;
    }

    bool PreTraverseCXXForRangeStmt(CXXForRangeStmt* stmt)
    {
        innermostLoop_.push(stmt);
        return true;
    }

    bool PostTraverseCXXForRangeStmt(CXXForRangeStmt* stmt, bool)
    {
        assert(!innermostLoop_.empty());
        assert(innermostLoop_.top() == stmt);
        (void)stmt;
        innermostLoop_.pop();
        return true;
    }

private:
    void run() override
    {
        if (preRun() && TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()))
        {
            postRun();
        }
    }

    Stmt const* getInnermostLoop() const
    {
        return innermostLoop_.empty() ? nullptr : innermostLoop_.top();
    }

    struct Data
    {
        Data(Stmt const* theInnermostLoop)
            : innermostLoop(theInnermostLoop)
        {
        }
        Stmt const* innermostLoop;
        llvm::Optional<Expr const*> singleUse;
    };

    std::stack<Stmt const*> innermostLoop_;
    std::map<VarDecl const*, Data> vars_;
};

loplugin::Plugin::Registration<ElideStringVar> elidestringvar("elidestringvar");
}

#endif

/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */