new clang plugin: loopvartoosmall

Idea from bubli - look for loops where the index variable is of such
size that it cannot cover the range revealed by examining the length
part of the condition.

So far, I have only run the plugin up till the VCL module.

Also the plugin deliberately excludes anything more complicated than a
straightforward incrementing for loop.

Change-Id: Ifced18b01c03ea537c64168465ce0b8287a42015

1 files changed, 119 insertions, 0 deletions

diff --git a/compilerplugins/clang/loopvartoosmall.cxx b/compilerplugins/clang/loopvartoosmall.cxx
new file mode 100644
index 000000000000..9cfa9f272444
--- /dev/null
+++ b/compilerplugins/clang/loopvartoosmall.cxx
@@ -0,0 +1,119 @@
+/* -*- 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 <string>
+#include <iostream>
+
+#include "plugin.hxx"
+#include "compat.hxx"
+#include "clang/AST/CXXInheritance.h"
+
+// Idea from bubli. Check that the index variable in a for loop is able to cover the range
+// revealed by the terminating condition.
+// If not, we might end up in an endless loop, or just not process certain parts.
+
+namespace {
+
+class LoopVarTooSmall:
+    public RecursiveASTVisitor<LoopVarTooSmall>, public loplugin::Plugin
+{
+public:
+    explicit LoopVarTooSmall(InstantiationData const & data): Plugin(data) {}
+
+    virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    bool VisitForStmt( const ForStmt* stmt );
+
+private:
+    StringRef getFilename(SourceLocation loc);
+
+};
+
+StringRef LoopVarTooSmall::getFilename(SourceLocation loc)
+{
+    SourceLocation spellingLocation = compiler.getSourceManager().getSpellingLoc(loc);
+    StringRef name { compiler.getSourceManager().getFilename(spellingLocation) };
+    return name;
+}
+
+bool LoopVarTooSmall::VisitForStmt( const ForStmt* stmt )
+{
+    if (ignoreLocation( stmt ))
+        return true;
+    // ignore SAL for now
+    StringRef aFileName = getFilename(stmt->getLocStart());
+    if (aFileName.startswith(SRCDIR "/sal/")) {
+        return true;
+    }
+
+    const Stmt* initStmt = stmt->getInit();
+    if (!initStmt || !isa<DeclStmt>(initStmt))
+        return true;
+    const DeclStmt* declStmt = dyn_cast<DeclStmt>(initStmt);
+    if (!declStmt->getDeclGroup().isSingleDecl())
+        return true;
+    const Decl* decl = declStmt->getSingleDecl();
+    if (!decl || !isa<VarDecl>(decl))
+        return true;
+    const VarDecl* varDecl = dyn_cast<VarDecl>(decl);
+    QualType qt = varDecl->getType();
+    if (!qt->isIntegralType(compiler.getASTContext()))
+        return true;
+    uint64_t qt1BitWidth = compiler.getASTContext().getTypeSize(qt);
+
+    if (!stmt->getCond() || !isa<BinaryOperator>(stmt->getCond()))
+        return true;
+    const BinaryOperator* binOp = dyn_cast<BinaryOperator>(stmt->getCond());
+    if (binOp->getOpcode() != BO_LT && binOp->getOpcode() != BO_LE)
+        return true;
+    const Expr* binOpRHS = binOp->getRHS();
+    // ignore complex expressions for now
+    if (isa<BinaryOperator>(binOpRHS))
+        return true;
+    if (isa<ImplicitCastExpr>(binOpRHS))
+    {
+        const ImplicitCastExpr* castExpr = dyn_cast<ImplicitCastExpr>(binOpRHS);
+        binOpRHS = castExpr->getSubExpr();
+    }
+    QualType qt2 = binOpRHS->getType();
+    if (!qt2->isIntegralType(compiler.getASTContext()))
+        return true;
+    // check for comparison with constants where the compiler just tends to give me the type as "int"
+    llvm::APSInt aIntResult;
+    uint64_t qt2BitWidth = compiler.getASTContext().getTypeSize(qt2);
+    if (binOpRHS->EvaluateAsInt(aIntResult, compiler.getASTContext())) {
+        if (aIntResult.getSExtValue() > 0 && aIntResult.getSExtValue() < 1<<7) {
+            qt2BitWidth = 8;
+        }
+        else if (aIntResult.getSExtValue() > 0 && aIntResult.getSExtValue() < 1<<15) {
+            qt2BitWidth = 16;
+        }
+        else if (aIntResult.getSExtValue() > 0 && aIntResult.getSExtValue() < 1L<<31) {
+            qt2BitWidth = 32;
+        }
+    }
+
+    if (qt1BitWidth < qt2BitWidth)
+    {
+        report(
+            DiagnosticsEngine::Warning,
+            "loop index variable is shorter than length type. " + qt.getAsString() + " < " + qt2.getAsString(),
+            stmt->getLocStart())
+          << stmt->getSourceRange();
+//        stmt->getCond()->dump();
+    }
+    return true;
+}
+
+
+loplugin::Plugin::Registration< LoopVarTooSmall > X("loopvartoosmall", false);
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */