[PATCH] Add support for unroll pragma

[Mark Heffernan]

I added a warning if the wrong pragma unroll syntax is used with CUDA.  When Tyler's change adding support for expressions in loop pragmas lands, I'll add a warning for the case when the pragma argument is not an integer literal in CUDA mode.  Responses to Aaron's comments inline.

On Wed, Jul 9, 2014 at 7:42 AM, Aaron Ballman <aaron.ballman at gmail.com> wrote:
> On Wed, Jul 9, 2014 at 2:14 AM, Mark Heffernan <meheff at google.com> wrote:
>> I also added "#pragma nounroll" as both icc and xlc support this pragma.
>
> Please split nounroll out into a separate patch. The idea is certainly
> reasonable, but it's preferable for patches to cover a limited,
> incremental change.

Done.

>> On Wed, Jul 2, 2014 at 7:54 AM, Aaron Ballman <aaron.ballman at gmail.com> wrote:
> Okay, I can see why that would happen. ClangAtterEmitter.cpp generates
> code for serialization and deserialization, but it doesn't have any
> way of handling additional members (since those are just copy/pasted
> into the attribute class definition itself).
>
> I wonder how horrible it would be to simply canonicalize based on
> compiler options when pretty printing, and skip this field entirely.
> Eg) when CUDA is on, pretty print does not emit the parens. When CUDA
> mode is off, it does emit the parens. Yes, this isn't *exactly* what
> the user wrote, but the semantics are identical either way.

It's now cannonicalized to the form with parentheses '#pragma unroll(n)'.  Tracking of the existence of parentheses is gone.

>> Index: include/clang/Basic/DiagnosticParseKinds.td
>> ===================================================================
>> --- include/clang/Basic/DiagnosticParseKinds.td
>> +++ include/clang/Basic/DiagnosticParseKinds.td
>> @@ -811,6 +811,9 @@
>>    InGroup<IgnoredPragmas>;
>>  def warn_pragma_expected_punc : Warning<
>>    "expected ')' or ',' in '#pragma %0'">, InGroup<IgnoredPragmas>;
>> +// - Generic errors
>> +def err_pragma_missing_argument : Error<
>> +  "missing argument to %0 directive">;
>
> Since it's a generic parsing diagnostic, presumably we know what kind
> of argument is missing, and we could tell the user that information.
> What's more, since pragmas can have multiple arguments, this doesn't
> say *which* argument is missing (there could be more than one).
>
> I also think the word "directive" could be dropped.

Created a generic diagnostic: "missing argument to '#pragma %0'; expected %1".  This new warning is also now shared with one pragma optimize warning.  Regarding stating which argument is missing, all of the pragmas using this warning only take a single argument.  I think it makes sense not to specify argument position unless multiple arguments are allowed.  That is, "missing first argument to '#pragma unroll'" suggests pragma unroll accepts more than one argument.  If this error is later used for pragmas with multiple parameters, the format string can be adjusted accordingly.

>>  def err_pragma_loop_precedes_nonloop : Error<
>> -  "expected a for, while, or do-while loop to follow the '#pragma clang loop' "
>> -  "directive">;
>> +  "expected a for, while, or do-while loop to follow the '%0' directive">;
>
> I would drop "directive" (and "the") here too.

Done.

http://reviews.llvm.org/D4297

Files:
  docs/ReleaseNotes.rst
  include/clang/Basic/Attr.td
  include/clang/Basic/AttrDocs.td
  include/clang/Basic/DiagnosticGroups.td
  include/clang/Basic/DiagnosticParseKinds.td
  include/clang/Basic/DiagnosticSemaKinds.td
  include/clang/Parse/Parser.h
  include/clang/Sema/LoopHint.h
  lib/Parse/ParsePragma.cpp
  lib/Parse/ParseStmt.cpp
  lib/Sema/SemaStmtAttr.cpp
  test/CodeGen/pragma-unroll.cpp
  test/PCH/pragma-loop.cpp
  test/Parser/pragma-loop.cpp
  test/Parser/pragma-unroll.cpp
  test/Parser/warn-cuda-compat.cu
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