[clang-tidy] New checker for redundant expressions.

Summary:
This checker finds redundant expression on both side of a binary operator.

The current implementation provide a function to check whether expressions
are equivalent. This implementation is able to recognize the common
subset encounter in C++ program. Side-effects like "x++" are not considered
to be equivalent.

There are many False Positives related to macros and to floating point
computations (detecting NaN). The checker is ignoring these cases.

Example:
```
    if( !dst || dst->depth != desired_depth ||
        dst->nChannels != desired_num_channels ||
        dst_size.width != src_size.width ||
        dst_size.height != dst_size.height )    <<--- bug
    {
```

Reviewers: alexfh

Subscribers: danielmarjamaki, fahlgren, jordan_rose, zaks.anna, Eugene.Zelenko, cfe-commits

Differential Revision: http://reviews.llvm.org/D19451

llvm-svn: 267574

1 files changed, 35 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.h b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.h
new file mode 100644
index 00000000000..80460a63d09
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.h
@@ -0,0 +1,35 @@
+//===--- RedundantExpressionCheck.h - clang-tidy-----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_REDUNDANT_EXPRESSION_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_REDUNDANT_EXPRESSION_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+/// Detect useless or suspicious redundant expressions.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/misc-redundant-expression.html
+class RedundantExpressionCheck : public ClangTidyCheck {
+public:
+  RedundantExpressionCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_REDUNDANT_EXPRESSION_H