[analyzer] Improves the logic of GenericTaintChecker identifying stdin.

Summary:
GenericTaintChecker can't recognize stdin in some cases. The reason is that `if (PtrTy->getPointeeType() == C.getASTContext().getFILEType()` does not hold when stdin is encountered.

My platform is ubuntu16.04 64bit, gcc 5.4.0, glibc 2.23. The definition of stdin is as follows:
```
__BEGIN_NAMESPACE_STD
/* The opaque type of streams.  This is the definition used elsewhere.  */
typedef struct _IO_FILE FILE;
___END_NAMESPACE_STD

  ...

/* The opaque type of streams.  This is the definition used elsewhere.  */
typedef struct _IO_FILE __FILE;   

  ...

/* Standard streams.  */
extern struct _IO_FILE *stdin;      /* Standard input stream.  */
extern struct _IO_FILE *stdout;     /* Standard output stream.  */
extern struct _IO_FILE *stderr;     /* Standard error output stream.  */
```

The type of stdin is as follows AST:
```
ElaboratedType 0xc911170'struct _IO_FILE'sugar
`-RecordType 0xc911150'struct _IO_FILE'
 `-CXXRecord 0xc923ff0'_IO_FILE'
```

`C.getASTContext().GetFILEType()` is as follows AST:
```
TypedefType 0xc932710 'FILE' sugar
|-Typedef 0xc9111c0 'FILE'
`-ElaboratedType 0xc911170 'struct _IO_FILE' sugar
  `-RecordType 0xc911150 'struct _IO_FILE'
      `-CXXRecord 0xc923ff0 '_IO_FILE'
```

So I think it's better to use `getCanonicalType()`.

Reviewers: zaks.anna, NoQ, george.karpenkov, a.sidorin

Reviewed By: zaks.anna, a.sidorin

Subscribers: a.sidorin, cfe-commits, xazax.hun, szepet, MTC

Differential Revision: https://reviews.llvm.org/D39159

llvm-svn: 326709

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
index 800bbf991d0..3186abebc26 100644
--- a/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
@@ -646,7 +646,8 @@ bool GenericTaintChecker::isStdin(const Expr *E, CheckerContext &C) {
     if ((D->getName().find("stdin") != StringRef::npos) && D->isExternC())
         if (const PointerType * PtrTy =
               dyn_cast<PointerType>(D->getType().getTypePtr()))
-          if (PtrTy->getPointeeType() == C.getASTContext().getFILEType())
+          if (PtrTy->getPointeeType().getCanonicalType() ==
+              C.getASTContext().getFILEType().getCanonicalType())
             return true;
   }
   return false;