r201607 - Experiment with making -Wunreachable-code more immediately useful by restricting warnings to those issued in the main file.

[David Blaikie]

On Tue, Feb 18, 2014 at 2:12 PM, Ted Kremenek <kremenek at apple.com> wrote:

> Author: kremenek
> Date: Tue Feb 18 16:12:10 2014
> New Revision: 201607
>
> URL: http://llvm.org/viewvc/llvm-project?rev=201607&view=rev
> Log:
> Experiment with making -Wunreachable-code more immediately useful by
> restricting warnings to those issued in the main file.
>

Seems simple enough (though one of these days I'll dredge up the CFG edge
improvements again to start fixing this more completely) - but a simple
test case would be nice to have too.


> This warning has a whole bunch of known false positives, much of them due
> to code that is "sometimes unreachable".  This can caused by code that
> is conditionally generated by the preprocessor, branches that are defined
> in terms of architecture-specific details (e.g., the size of a type), and
> so on.  While these are all good things to address one by one, the reality
> is that this warning has received little love lately.  By restricting
> its purvue, we can focus on the top issues effecting main files, which
> should be smaller, and then gradually widen the scope.
>
> Modified:
>     cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp
>
> Modified: cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp?rev=201607&r1=201606&r2=201607&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp (original)
> +++ cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp Tue Feb 18 16:12:10 2014
> @@ -66,6 +66,12 @@ namespace {
>      UnreachableCodeHandler(Sema &s) : S(s) {}
>
>      void HandleUnreachable(SourceLocation L, SourceRange R1, SourceRange
> R2) {
> +      // As a heuristic prune all diagnostics not in the main file.
>  Currently
> +      // the majority of warnings in headers are false positives.  These
> +      // are largely caused by configuration state, e.g. preprocessor
> +      // defined code, etc.
> +      if (!S.getSourceManager().isInMainFile(L))
> +        return;
>        S.Diag(L, diag::warn_unreachable) << R1 << R2;
>      }
>    };
>
>
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