[PATCH] D20811: [analyzer] Model some library functions

[Artem Dergachev via cfe-commits]

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I've put together a simple checker that throws no warnings, but models some library functions, which has already helped us to suppress some false positives in other checkers in our runs.

For pure functions, i chose the old `evalCall()` approach instead of the body-farm approach because i wanted to produce less state splits. For example, this checker produce a single exploded graph branch for `ispunct()`'s non-zero branch, when its argument is in range ['!', '/'] U [':', '@'] U ['[', '`'] U ['{', '~'] - i'm not sure if there's a way to write this out with if's and produce less than 4 branches. (Do we have any plans on merging branches more aggressively during analysis?) Because these functions are pure, we'd hardly ever want to catch them with`evalCall()` again in another checker.

Additionally, this checker's brace-initializers for function specifications are quite short - of course they're limited to very simple cases - the list of these cases can be expanded though.

The checker doesn't seem to be noticeably degrading performance. Here's an example of a false positve squashed: {F2000003} Here `line` is taken to be "", the `line++` statement is executed at least once (by looking at the exploded graph; there's lack of "entering loop body" diagnostic piece because loop condition has complicated CFG, which is why it fails to highlight - a separate issue), and the analyzer fails to realize that isspace('\0') is false.

http://reviews.llvm.org/D20811

Files:
  include/clang/StaticAnalyzer/Checkers/Checkers.td
  lib/StaticAnalyzer/Checkers/CMakeLists.txt
  lib/StaticAnalyzer/Checkers/LibraryFunctionsChecker.cpp
  test/Analysis/library-functions.c

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