new loplugin sequentialassign

Look for places we are assigning to the same variable twice
in succession, which means we can simplify that to a single assign

Change-Id: I499d20e28f5595e81e927bef8e1bf364eea8ba91
Reviewed-on: https://gerrit.libreoffice.org/70531
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 426 insertions, 0 deletions

diff --git a/compilerplugins/clang/sequentialassign.cxx b/compilerplugins/clang/sequentialassign.cxx
new file mode 100644
index 000000000000..bc674694f8f1
--- /dev/null
+++ b/compilerplugins/clang/sequentialassign.cxx
@@ -0,0 +1,331 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * 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/.
+ */
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "plugin.hxx"
+#include "check.hxx"
+#include "clang/AST/CXXInheritance.h"
+#include "clang/AST/StmtVisitor.h"
+
+/**
+    This is a kind of simplified dead-store analysis.
+
+    We are looking for patterns like:
+      Foo x = a;
+      x = b;
+    which can be simplified to
+        x = b
+
+    or
+        Foo x = a;
+        x = f(x)
+    which can be simplified to
+        Foo x = f(a)
+
+   TODO Improve this plugin to make it safer. We should really be checking the following
+   conditions inside the RHS of the second statement:
+     If the variable is having it's address taken, or a non-const method called on it,
+     on passed by non-const-ref.
+*/
+
+namespace
+{
+//static bool startswith(const std::string& rStr, const char* pSubStr) {
+//    return rStr.compare(0, strlen(pSubStr), pSubStr) == 0;
+//}
+class SequentialAssign : public loplugin::FilteringPlugin<SequentialAssign>
+{
+public:
+    explicit SequentialAssign(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual void run() override
+    {
+        std::string fn(handler.getMainFileName());
+        loplugin::normalizeDotDotInFilePath(fn);
+        // places where the existing code style just looks better
+        // TODO lots of these would be unnecessary if I taught the plugin
+        // to ignore vars which are assigned to repeatedly
+        if (fn == SRCDIR "/vcl/source/helper/commandinfoprovider.cxx"
+            || fn == SRCDIR "/basegfx/source/polygon/b2dpolygonclipper.cxx"
+            || fn == SRCDIR "/i18nlangtag/source/isolang/insys.cxx"
+            || fn == SRCDIR "/vcl/unx/generic/fontmanager/fontconfig.cxx"
+            || fn == SRCDIR "/svtools/source/filter/exportdialog.cxx"
+            || fn == SRCDIR "/svtools/source/control/ruler.cxx"
+            || fn == SRCDIR "/basic/qa/cppunit/test_scanner.cxx"
+            || fn == SRCDIR "/basic/source/uno/namecont.cxx"
+            || fn == SRCDIR "/test/source/sheet/xnamedrange.cxx"
+            || fn == SRCDIR "/i18npool/qa/cppunit/test_breakiterator.cxx"
+            || fn == SRCDIR "/i18npool/source/localedata/LocaleNode.cxx"
+            || fn == SRCDIR "/i18npool/source/transliteration/transliteration_Ignore.cxx"
+            || fn == SRCDIR "/i18npool/qa/cppunit/test_textsearch.cxx"
+            || fn == SRCDIR "/framework/source/jobs/jobdata.cxx"
+            || fn == SRCDIR "/framework/source/services/pathsettings.cxx"
+            || fn == SRCDIR "/xmloff/source/chart/SchXMLTools.cxx"
+            || fn == SRCDIR "/svx/source/tbxctrls/Palette.cxx"
+            || fn == SRCDIR "/svx/source/sdr/contact/objectcontactofpageview.cxx"
+            || fn == SRCDIR "/svx/source/form/fmservs.cxx"
+            || fn == SRCDIR "/svx/source/svdraw/svdograf.cxx"
+            || fn == SRCDIR "/svx/source/accessibility/AccessibleShape.cxx"
+            || fn == SRCDIR "/svx/source/fmcomp/fmgridcl.cxx"
+            || fn == SRCDIR "/chart2/source/tools/CharacterProperties.cxx"
+            || fn == SRCDIR "/svx/source/dialog/dialcontrol.cxx"
+            || fn == SRCDIR "/connectivity/source/commontools/TTableHelper.cxx"
+            || fn == SRCDIR "/svx/source/dialog/_bmpmask.cxx"
+            || fn == SRCDIR "/media/noel/disk2/libo4/cui/source/dialogs/SignSignatureLineDialog.cxx"
+            || fn == SRCDIR "/filter/source/msfilter/msdffimp.cxx"
+            || fn == SRCDIR "/filter/source/flash/swffilter.cxx"
+            || fn == SRCDIR "/cui/source/dialogs/SignSignatureLineDialog.cxx"
+            || fn == SRCDIR "/cui/source/dialogs/screenshotannotationdlg.cxx"
+            || fn == SRCDIR "/cui/source/options/optupdt.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/querydesign/querycontroller.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/dlg/DbAdminImpl.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/querydesign/JoinController.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/misc/TokenWriter.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/misc/TokenWriter.cxx"
+            || fn == SRCDIR "/dbaccess/source/ui/misc/dbsubcomponentcontroller.cxx"
+            || fn == SRCDIR "/dbaccess/source/core/api/querycomposer.cxx"
+            || fn == SRCDIR "/desktop/source/lib/init.cxx"
+            || fn == SRCDIR "/lotuswordpro/source/filter/lwpfribmark.cxx"
+            || fn == SRCDIR "/tools/qa/cppunit/test_color.cxx"
+            || fn == SRCDIR "/sc/qa/unit/ucalc.cxx"
+            || fn == SRCDIR "/sc/source/ui/view/printfun.cxx"
+            || fn == SRCDIR "/sc/source/ui/view/preview.cxx"
+            || fn == SRCDIR "/sw/source/core/doc/tblafmt.cxx"
+            || fn == SRCDIR "/sw/source/core/draw/dflyobj.cxx"
+            || fn == SRCDIR "/sw/source/core/doc/DocumentDrawModelManager.cxx"
+            || fn == SRCDIR "/sw/source/core/edit/edfcol.cxx"
+            || fn == SRCDIR "/sw/source/filter/ww8/ww8toolbar.cxx"
+            || fn == SRCDIR "/sw/source/ui/fldui/fldvar.cxx"
+            || fn == SRCDIR "/sw/source/filter/ww8/ww8atr.cxx"
+            || fn == SRCDIR "/sd/source/ui/accessibility/AccessiblePageShape.cxx"
+            || fn == SRCDIR "/xmlsecurity/source/xmlsec/nss/nssinitializer.cxx"
+            || fn == SRCDIR "/sd/source/ui/slidesorter/cache/SlsRequestFactory.cxx"
+            || fn == SRCDIR "/sd/source/ui/framework/configuration/ResourceId.cxx"
+            || fn == SRCDIR "/sd/source/filter/html/htmlex.cxx"
+            || fn == SRCDIR "/starmath/source/cfgitem.cxx"
+            || fn == SRCDIR "/ucb/source/ucp/ftp/ftpurl.cxx"
+            || fn == SRCDIR "/starmath/source/node.cxx"
+            || fn == SRCDIR "/ucb/source/ucp/cmis/certvalidation_handler.cxx"
+            || fn == SRCDIR "/reportdesign/source/ui/inspection/GeometryHandler.cxx"
+            || fn == SRCDIR "/reportdesign/source/core/api/ReportDefinition.cxx"
+            || fn == SRCDIR "/test/source/table/tablerow.cxx"
+            || fn == SRCDIR "/basegfx/test/B2DHomMatrixTest.cxx"
+            || fn == SRCDIR "/comphelper/qa/unit/base64_test.cxx"
+            || fn == SRCDIR "/testtools/source/bridgetest/bridgetest.cxx"
+            || fn == SRCDIR "/comphelper/qa/string/test_string.cxx"
+            || fn == SRCDIR "/cppu/qa/test_unotype.cxx"
+            || fn == SRCDIR "/cppu/qa/cppumaker/test_cppumaker.cxx"
+            || fn == SRCDIR "/o3tl/qa/test-lru_map.cxx" || fn == SRCDIR "/svl/qa/unit/svl.cxx"
+            || fn == SRCDIR "/chart2/qa/extras/PivotChartTest.cxx"
+            || fn == SRCDIR "/chart2/qa/extras/chart2export.cxx"
+            || fn == SRCDIR "/writerfilter/qa/cppunittests/misc/misc.cxx"
+            || fn == SRCDIR "/sw/qa/extras/ww8export/ww8export.cxx"
+            || fn == SRCDIR "/sw/qa/extras/uiwriter/uiwriter.cxx")
+            return;
+        // inside ifdef
+        if (fn == SRCDIR "/vcl/source/filter/png/pngread.cxx"
+            || fn == SRCDIR "/vcl/source/window/syschild.cxx"
+            || fn == SRCDIR "/sal/osl/unx/security.cxx"
+            || fn == SRCDIR "/vcl/source/filter/png/pngwrite.cxx"
+            || fn == SRCDIR "/svtools/source/control/inettbc.cxx"
+            || fn == SRCDIR "/canvas/source/cairo/cairo_textlayout.cxx"
+            || fn == SRCDIR "/sal/qa/osl/file/osl_File.cxx")
+            return;
+        // taking address of variable
+        if (fn == SRCDIR "/vcl/unx/generic/dtrans/X11_selection.cxx")
+            return;
+        // other
+        if (fn == SRCDIR "/sc/source/core/tool/scmatrix.cxx"
+            || fn == SRCDIR "/sal/qa/rtl/oustringbuffer/test_oustringbuffer_assign.cxx")
+            return;
+
+        TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitCompoundStmt(CompoundStmt const*);
+
+private:
+    const VarDecl* findSimpleAssign(Stmt const*);
+    bool isSimpleRHS(Expr const*);
+    Expr const* ignore(Expr const*);
+    void checkForSecondAssign(Stmt const* firstStmt, Stmt const* stmt, VarDecl const* varDecl);
+};
+
+bool SequentialAssign::VisitCompoundStmt(CompoundStmt const* compoundStmt)
+{
+    if (ignoreLocation(compoundStmt))
+        return true;
+
+    auto it = compoundStmt->body_begin();
+    while (true)
+    {
+        if (it == compoundStmt->body_end())
+            break;
+        auto firstStmt = *it;
+        const VarDecl* foundVars = findSimpleAssign(firstStmt);
+        // reference types have slightly weird behaviour
+        if (!foundVars || foundVars->getType()->isReferenceType())
+        {
+            ++it;
+            continue;
+        }
+        ++it;
+        if (it == compoundStmt->body_end())
+            break;
+        checkForSecondAssign(firstStmt, *it, foundVars);
+    }
+
+    return true;
+}
+
+void SequentialAssign::checkForSecondAssign(Stmt const* firstStmt, Stmt const* stmt,
+                                            VarDecl const* varDecl)
+{
+    if (auto exprCleanup = dyn_cast<ExprWithCleanups>(stmt))
+        stmt = exprCleanup->getSubExpr();
+
+    if (auto operatorCall = dyn_cast<CXXOperatorCallExpr>(stmt))
+    {
+        if (operatorCall->getOperator() == OO_Equal)
+        {
+            if (auto declRefExprLHS = dyn_cast<DeclRefExpr>(ignore(operatorCall->getArg(0))))
+                if (declRefExprLHS->getDecl() == varDecl)
+                {
+                    firstStmt->dump();
+                    report(DiagnosticsEngine::Warning,
+                           "simplify by merging with the preceding assignment",
+                           compat::getBeginLoc(stmt))
+                        << stmt->getSourceRange();
+                }
+        }
+        return;
+    }
+
+    if (auto binaryOp = dyn_cast<BinaryOperator>(stmt))
+    {
+        if (binaryOp->getOpcode() == BO_Assign)
+        {
+            if (auto declRefExpr = dyn_cast<DeclRefExpr>(ignore(binaryOp->getLHS())))
+                if (declRefExpr->getDecl() == varDecl)
+                {
+                    firstStmt->dump();
+                    report(DiagnosticsEngine::Warning,
+                           "simplify by merging with the preceding assignment",
+                           compat::getBeginLoc(stmt))
+                        << stmt->getSourceRange();
+                }
+        }
+    }
+}
+
+const VarDecl* SequentialAssign::findSimpleAssign(Stmt const* stmt)
+{
+    if (auto declStmt = dyn_cast<DeclStmt>(stmt))
+        if (declStmt->isSingleDecl())
+            if (auto varDeclLHS = dyn_cast_or_null<VarDecl>(declStmt->getSingleDecl()))
+            {
+                if (varDeclLHS->getStorageDuration() == SD_Static)
+                    return nullptr;
+                // if it's call-style init (e.g. OUString s("xxx")), we only treat
+                // it as simple if it only contains a variable in the call
+                // (e.g. OUString s(x))
+                if (varDeclLHS->getInitStyle() == VarDecl::InitializationStyle::CallInit)
+                {
+                    auto cxxConstructExpr
+                        = dyn_cast<CXXConstructExpr>(ignore(varDeclLHS->getInit()));
+                    if (cxxConstructExpr)
+                    {
+                        if (cxxConstructExpr->getNumArgs() == 0)
+                            return varDeclLHS;
+                        if (cxxConstructExpr->getNumArgs() > 1)
+                            return nullptr;
+                        if (!isa<DeclRefExpr>(ignore(cxxConstructExpr->getArg(0))))
+                            return nullptr;
+                    }
+                }
+                if (auto init = varDeclLHS->getInit())
+                    if (isSimpleRHS(init))
+                        return varDeclLHS;
+            }
+    if (auto operatorCall = dyn_cast<CXXOperatorCallExpr>(stmt))
+        if (operatorCall->getOperator() == OO_Equal)
+            if (auto declRefExprLHS = dyn_cast<DeclRefExpr>(ignore(operatorCall->getArg(0))))
+                if (auto varDeclLHS = dyn_cast<VarDecl>(declRefExprLHS->getDecl()))
+                    if (isSimpleRHS(operatorCall->getArg(1)))
+                        return varDeclLHS;
+    if (auto binaryOp = dyn_cast<BinaryOperator>(stmt))
+        if (binaryOp->getOpcode() == BO_Assign)
+            if (auto declRefExprLHS = dyn_cast<DeclRefExpr>(ignore(binaryOp->getLHS())))
+                if (auto varDeclLHS = dyn_cast<VarDecl>(declRefExprLHS->getDecl()))
+                    if (isSimpleRHS(binaryOp->getRHS()))
+                        return varDeclLHS;
+    return nullptr;
+}
+
+/**
+  Does the first statement have a relatively simply RHS we can inline into the second statement?
+*/
+bool SequentialAssign::isSimpleRHS(Expr const* expr)
+{
+    expr = ignore(expr);
+
+    // code like
+    //    Point aCurPos = rGlyphs
+    // always has a CXXConstructExpr wrapping the RHS
+    if (auto cxxConstructExpr = dyn_cast<CXXConstructExpr>(expr))
+        if (cxxConstructExpr->getNumArgs() == 1)
+            expr = ignore(cxxConstructExpr->getArg(0));
+
+    if (!expr->isValueDependent()
+        && expr->isConstantInitializer(compiler.getASTContext(), false /*ForRef*/))
+        return true;
+    if (isa<CXXMemberCallExpr>(expr))
+        return false;
+    if (isa<CXXOperatorCallExpr>(expr))
+        return false;
+    if (isa<UserDefinedLiteral>(expr))
+        return true;
+    if (isa<CallExpr>(expr))
+        return false;
+    if (isa<CastExpr>(expr))
+        return false;
+    if (isa<ArraySubscriptExpr>(expr))
+        return false;
+    if (isa<BinaryOperator>(expr))
+        return false;
+    if (isa<ConditionalOperator>(expr))
+        return false;
+    if (isa<UnaryOperator>(expr))
+        return false;
+    if (isa<CXXNewExpr>(expr))
+        return false;
+    if (auto memberExpr = dyn_cast<MemberExpr>(expr))
+        return isSimpleRHS(memberExpr->getBase());
+
+    return true;
+}
+
+Expr const* SequentialAssign::ignore(Expr const* expr)
+{
+    return expr->IgnoreImplicit()->IgnoreParens()->IgnoreImplicit();
+}
+
+// Off by default because of safety concerns, see TODO at top
+loplugin::Plugin::Registration<SequentialAssign> X("sequentialassign", false);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/compilerplugins/clang/test/sequentialassign.cxx b/compilerplugins/clang/test/sequentialassign.cxx
new file mode 100644
index 000000000000..e656e1a7a304
--- /dev/null
+++ b/compilerplugins/clang/test/sequentialassign.cxx
@@ -0,0 +1,95 @@
+/* -*- 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/.
+ */
+
+#include <rtl/ustring.hxx>
+
+namespace test1
+{
+void f(OUString s1)
+{
+    OUString s2 = s1;
+    // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+    s2 = s2.getToken(0, '(');
+}
+}
+
+namespace test2
+{
+OUString s2;
+void f(OUString s1)
+{
+    s2 = s1;
+    // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+    s2 = s2.getToken(0, '(');
+}
+}
+
+namespace test3
+{
+struct VolumeInfo
+{
+    OUString getFileSystemName();
+};
+OUString aNullURL("");
+void f(VolumeInfo _aVolumeInfo)
+{
+    OUString aFileSysName(aNullURL);
+    // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+    aFileSysName = _aVolumeInfo.getFileSystemName();
+}
+}
+
+namespace test4
+{
+struct B3DVector
+{
+    B3DVector getPerpendicular();
+};
+void f(B3DVector aNewVPN)
+{
+    B3DVector aNewToTheRight = aNewVPN;
+    // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+    aNewToTheRight = aNewToTheRight.getPerpendicular();
+}
+}
+
+namespace test5
+{
+void f(OUString s, int x)
+{
+    int nPos = x;
+    // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+    nPos = s.indexOf("x", nPos);
+}
+}
+
+namespace test6
+{
+void f()
+{
+    OUString s2("xxxx");
+    s2 = s2.getToken(0, '('); // no warning expected
+}
+}
+
+namespace test7
+{
+class Class1
+{
+    OUString m_field1;
+    void foo(Class1& rOther)
+    {
+        OUString s = rOther.m_field1;
+        // expected-error@+1 {{simplify by merging with the preceding assignment [loplugin:sequentialassign]}}
+        s = s.copy(1, 2);
+    }
+};
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */