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

[Hans Wennborg via cfe-commits]

The change seems straight-forward, well reviewed and has been in the
tree for a while, so I've merged it to 3.9 in r277075.

Thanks,
Hans

On Mon, Jul 25, 2016 at 1:51 PM, Hans Wennborg <hans at chromium.org> wrote:
> 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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