[cfe-dev] Odd behaviour with '-save-temps' and OpenCL files

Mon Nov 7 08:34:44 PST 2016

@Martin: Have you tried to run `clang -v ...` to show the actual processing, and assuming it gives a sensible output, try to re-run the failing step (which I think is `cc1 ... filename.i`) with `-x cl`, and see if that resolves it?

This is interesting.  So I used ‘-v’ and I see ‘-x cpp-output’ in the command-line - didn’t even know that value existed! - and if I replace it with ‘-x cl’ is works perfectly, so your hunch is spot-on.  But is also means that the ‘-x cpp-output’ option is determining source language based on the extension (‘.i’ or ‘.ii’).

            MartinO

From: mats.o.petersson at googlemail.com [mailto:mats.o.petersson at googlemail.com] On Behalf Of mats petersson
Sent: 07 November 2016 15:30
To: Martin J. O'Riordan <Martin.ORiordan at movidius.com>
Cc: Joerg Sonnenberger <joerg at bec.de>; cfe-dev <cfe-dev at lists.llvm.org>
Subject: Re: [cfe-dev] Odd behaviour with '-save-temps' and OpenCL files

Assuming `#pragma clang language OpenCL` works, that seems like a neat thing that can be inserted as a "pre-include header" (as a constant string in the compiler). However, I'm not sure that clang does this in conjunction with the preprocessor as it is now - or that there is a simple way to achieve it - in which case, the other solution is to add some code to "remember" the language picked from the extension, and passing that to the parser step (cc1?) after preprocessing. 

--

Mats

On 7 November 2016 at 12:57, Martin J. O'Riordan <martin.oriordan at movidius.com <mailto:martin.oriordan at movidius.com> > wrote:

When the source is a C file, the pre-processed file has the extension ‘.i’, and when it is a C++ file the pre-processed file has the extension ‘.ii’.  Perhaps CL files need a 3rd convention for naming the pre-processed file, and eventually something similar if the FORTRAN front-end is available?  I don’t compile CUDA files, and they may have a similar problem.

Even passing ‘-x cl -c -save-temps’ does not solve it, so the knowledge that it is an OpenCL source appears to be lost.

            MartinO

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org <mailto:cfe-dev-bounces at lists.llvm.org> ] On Behalf Of mats petersson via cfe-dev
Sent: 07 November 2016 10:56
To: Joerg Sonnenberger <joerg at bec.de <mailto:joerg at bec.de> >; Clang Dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org> >
Subject: Re: [cfe-dev] Odd behaviour with '-save-temps' and OpenCL files

And how does the parser know from the preprocessed output that it is CL rather than C that it's parsing? I suspect it's the ".cl" part of the name of "filename.cl <http://filename.cl> " that determines that it's CL code in the first place, if that gets replaced with "filename.i", the parser will just say "Ah, it's C-code and has already been preprocessed".

Maybe the parser needs a `-x cl` or similar to ensure that the parser knows it's CL-code?

I know that many of the CL parsing things have `if (langOpts.OpenCL) ...` in the parser and various other places. If we have a multi-pass way of running the compiler, it will potentially lose that information when it gets to the next step, is my thinking. I may of course be wrong, and the problem is with something else.

--

Mats

On 6 November 2016 at 11:04, Joerg Sonnenberger via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org> > wrote:

On Sun, Nov 06, 2016 at 10:01:05AM +0000, mats petersson via cfe-dev wrote:
> My guess, and it's only a guess, is that -save-temps causes the compiler to
> run each step on those files, by executing independent processes, rather
> than the usual "run all steps in parallel" - in my understanding, Clang
> doesn't actually work in the "old style cc way" and running several
> processes with files produced between each step.

Yes and no. -svae-temps will run the parser on the preprocessed output,
so all macro-expansion knowledge is missing. That changes the impact of
a number of warnings like redundant braces. Pragmas are still preserved
in the code though. It would be a bug in the OpenCL integration if the
pragmas are no longer processed OR if pragmas are silently attached to
macros by position.

Joerg

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