[clang-tidy] Add new checker for comparison with runtime string functions.

Summary:
This checker is validating suspicious usage of string compare functions.

Example:
```
  if (strcmp(...))       // Implicitly compare to zero
  if (!strcmp(...))      // Won't warn
  if (strcmp(...) != 0)  // Won't warn
```

This patch was checked over large amount of code.
There is three checks:
  [*] Implicit comparator to zero (coding-style, many warnings found),
  [*] Suspicious implicit cast to non-integral (bugs!?, almost none found),
  [*] Comparison to suspicious constant (bugs!?, found two cases),

Example:
[[https://github.com/kylepjohnson/sigma/blob/master/sigma/native-installers/debian/dependencies/files/opt/sigma/E/HEURISTICS/che_to_precgen.c |
https://github.com/kylepjohnson/sigma/blob/master/sigma/native-installers/debian/dependencies/files/opt/sigma/E/HEURISTICS/che_to_precgen.c]]

```
      else if(strcmp(id, "select") == 0)
      {
         array->array[i].key1 = 25;
      }
      else if(strcmp(id, "sk") == 28)      // BUG!?
      {
         array->array[i].key1 = 20;
      }
```

Reviewers: alexfh

Subscribers: Eugene.Zelenko, cfe-commits

Differential Revision: http://reviews.llvm.org/D18703

llvm-svn: 267009

1 files changed, 3 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp b/clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp
index 1d667b50161..aaeddeded21 100644
--- a/clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp
@@ -37,6 +37,7 @@
 #include "StringLiteralWithEmbeddedNulCheck.h"
 #include "SuspiciousMissingCommaCheck.h"
 #include "SuspiciousSemicolonCheck.h"
+#include "SuspiciousStringCompareCheck.h"
 #include "SwappedArgumentsCheck.h"
 #include "ThrowByValueCatchByReferenceCheck.h"
 #include "UndelegatedConstructor.h"
@@ -106,6 +107,8 @@ public:
         "misc-suspicious-missing-comma");
     CheckFactories.registerCheck<SuspiciousSemicolonCheck>(
         "misc-suspicious-semicolon");
+    CheckFactories.registerCheck<SuspiciousStringCompareCheck>(
+        "misc-suspicious-string-compare");    
     CheckFactories.registerCheck<SwappedArgumentsCheck>(
         "misc-swapped-arguments");
     CheckFactories.registerCheck<ThrowByValueCatchByReferenceCheck>(