r276653 - Support '#pragma once' in headers when using PCH

[Hans Wennborg via cfe-commits]

Should me merge this to 3.9?

On Mon, Jul 25, 2016 at 10:17 AM, Sunil Srivastava via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Author: ssrivastava
> Date: Mon Jul 25 12:17:06 2016
> New Revision: 276653
>
> URL: http://llvm.org/viewvc/llvm-project?rev=276653&view=rev
> Log:
> Support '#pragma once' in headers when using PCH
>
> The '#pragma once' directive was erroneously ignored when encountered
> in the header-file specified in generate-PCH-mode. This resulted in
> compile-time errors in some cases with legal code, and also a misleading
> warning being produced.
>
> Patch by Warren Ristow!
>
> Differential Revision: http://reviews.llvm.org/D19815
>
> Added:
>     cfe/trunk/test/PCH/Inputs/pragma-once.h
>     cfe/trunk/test/PCH/pragma-once.c
> Modified:
>     cfe/trunk/lib/Lex/Pragma.cpp
>
> Modified: cfe/trunk/lib/Lex/Pragma.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Lex/Pragma.cpp?rev=276653&r1=276652&r2=276653&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Lex/Pragma.cpp (original)
> +++ cfe/trunk/lib/Lex/Pragma.cpp Mon Jul 25 12:17:06 2016
> @@ -352,7 +352,9 @@ void Preprocessor::HandleMicrosoft__prag
>  /// HandlePragmaOnce - Handle \#pragma once.  OnceTok is the 'once'.
>  ///
>  void Preprocessor::HandlePragmaOnce(Token &OnceTok) {
> -  if (isInPrimaryFile()) {
> +  // Don't honor the 'once' when handling the primary source file, unless
> +  // this is a prefix to a TU, which indicates we're generating a PCH file.
> +  if (isInPrimaryFile() && TUKind != TU_Prefix) {
>      Diag(OnceTok, diag::pp_pragma_once_in_main_file);
>      return;
>    }
>
> Added: cfe/trunk/test/PCH/Inputs/pragma-once.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/PCH/Inputs/pragma-once.h?rev=276653&view=auto
> ==============================================================================
> --- cfe/trunk/test/PCH/Inputs/pragma-once.h (added)
> +++ cfe/trunk/test/PCH/Inputs/pragma-once.h Mon Jul 25 12:17:06 2016
> @@ -0,0 +1,5 @@
> +#pragma once
> +
> +/* For use with the pragma-once.c test */
> +
> +int x = 3;
>
> Added: cfe/trunk/test/PCH/pragma-once.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/PCH/pragma-once.c?rev=276653&view=auto
> ==============================================================================
> --- cfe/trunk/test/PCH/pragma-once.c (added)
> +++ cfe/trunk/test/PCH/pragma-once.c Mon Jul 25 12:17:06 2016
> @@ -0,0 +1,13 @@
> +// Test this without pch.
> +// RUN: %clang_cc1 -include %S/Inputs/pragma-once.h -fsyntax-only -verify %s
> +
> +// Test with pch.
> +// RUN: %clang_cc1 -emit-pch -o %t %S/Inputs/pragma-once.h
> +// RUN: %clang_cc1 -include-pch %t -fsyntax-only -verify %s
> +
> +// expected-no-diagnostics
> +
> +// Including "pragma-once.h" twice, to verify the 'once' aspect is honored.
> +#include "Inputs/pragma-once.h"
> +#include "Inputs/pragma-once.h"
> +int foo(void) { return 0; }
>
>
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