kimgr added a comment.
>> Can you test what happens when you do clang-cl.exe /Yc stdafx.h /Tp >> stdafx.h, i.e. compile the header > > directly as C++ code and generate .pch from it? The normal MSVC modus > operandi is to have stdafx.h > > included in all source files (with /Yu) and stdafx.cpp to generate it > (with /Yc). That stdafx.cpp file serves > > no purpose, so I've played this trick to generate PCH from the header > directly. If it works, it might also > > be useful for your tests. > > It isn't always the case that the .cpp file serves no purpose. It's true that > the MS project generators give you this setup but we've seen many projects > over the years that use a regular source file with code in it to generate the > PCH. The > object file generated during PCH create can have real code and the > compiler can take advantage of that fact by compiling less code in the > compilation units that use the PCH [...] Cool, it's never occurred to me that the source file has any other purpose than including the pch header. > I am not sure about your command: clang-cl.exe /Yc stdafx.h /Tp stdafx.h. The > space makes this a compile with just > /Yc (no through header). This patch doesn't address /Yc without the through > header. Something like clang-cl /Yc > /Tpstdafx.h would probably work if/when that is implemented. I no longer have access to an MSVC environment, so I can't spell out the exact command, but I was trying to phrase a command that generates a PCH from the through-header *without a distinct source file*. It's proved to be a useful trick. I didn't mean to omit the through header, let's try again: cl.exe /Ycstdafx.h /TP stdafx.h or if that doesn't work, a /FI switch may be required, I can't remember for sure what we did: cl.exe /Ycstdafx.h /TP /FI stdafx.h stdafx.h >> I think the current skip-warning is over-specific -- what if I put an inline >> function before my PCH include? > > A global variable? A #pragma? Or am I misunderstanding what skipping > does? It seems to me that any > > non-comment tokens before the PCH #include should raise a warning. > > Not any tokens. The through header "feature" compiles all the code in the > file up to the through header. > So normally you are used to seeing just comments and #include <stdafx.h>. > That's one usage but your > PCH can be created from a source like this [...] Thanks for the example, I must have misunderstood how MSVC PCHs work. With that background, the warning seems fine. >> I find the "through header" terminology is a little hard to interpret, but I >> did find it on MSDN, so maybe it's well established. > > Sorry about the terminology. I've been responsible for emulating this PCH > mechanism for many years so I may be one > of the few that understands it. I did try to keep that terminology out of > the diagnostics but I don't really have a better > name for through header. :) Sounds like it's well-established! https://reviews.llvm.org/D46652 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
