[PATCH] D46652: [clang-cl, PCH] Implement support for MS-style PCH through headers

Mike Rice via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu Jul 5 09:57:35 PDT 2018

mikerice added inline comments.

Comment at: include/clang/Driver/CC1Options.td:604
+  HelpText<"When creating a pch stop at this file.  When using a pch start "
+           "after this file.">;
 def fno_pch_timestamp : Flag<["-"], "fno-pch-timestamp">,
hans wrote:
> mikerice wrote:
> > hans wrote:
> > > The "through header" terminology was new to me, and I didn't see it when browsing the MSDN articles about precompiled headers. The HelpText here probably isn't the right place, but it would be good if the term could be documented somewhere to make it clearer exactly what the behaviour is. It's not really obvious to me what "stop at this file" and "start after this file"  means. I can guess, but it would be nice if it were more explicit :-)
> > You definitely have to look hard at the MSDN docs to find mention of through headers.  If you look at the documentation for /Yc and /Yu you can see some vague references.  I think it may have been more prominent many years ago. 
> > 
> > The MSDN page says "For /Yc, filename specifies the point at which precompilation stops; the compiler precompiles all code though(sic) filename..." https://msdn.microsoft.com/en-us/library/z0atkd6c.aspx
> > 
> > I'll look for a place to document this better in a comment at least.
> > 
> > 
> Thanks for the pointer. Yeah, a clear explanation in a comment somewhere would be really helpful. Another idea might be to have a little "precompiled headers" section in the clang-cl section of docs/UsersManual.rst. Maybe we could do a better job than MS at explaining it precisely? :-)
Thanks for the review.  In the last patch I updated the comment in PreprocessorOptions.h  to better explain what a through header is.  I like the idea of explaining this in UsersManual.rst.  I'll work on that in the next few weeks. 


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