[cfe-dev] Precompiled headers

[Richard Smith via cfe-dev]

On Dec 11, 2015 7:54 AM, "Russell Wallace via cfe-dev" <
cfe-dev at lists.llvm.org> wrote:
>
> I'm having a go at using precompiled headers, but it doesn't seem to be
working. What am I doing wrong?
>
> C:\test>type a.h
> #include <iostream>
> using namespace std;
>
> C:\test>type a.cpp
> #include "a.h"
>
> int main() {
>         cout << "test\n";
>         return 0;
> }
>
> C:\test>clang --version
> clang version 3.7.0 (tags/RELEASE_370/final)
> Target: x86_64-pc-windows-msvc
> Thread model: posix
>
> C:\test>clang -fms-compatibility-version=19 -x c++-header a.h
>
> C:\test>dir
>  Volume in drive C is OS
>  Volume Serial Number is C685-B1F1
>
>  Directory of C:\test
>
> 11/12/2015  15:51    <DIR>          .
> 11/12/2015  15:51    <DIR>          ..
> 11/12/2015  15:45                67 a.cpp
> 11/12/2015  15:44                41 a.h
> 11/12/2015  15:51         4,677,904 a.h.gch
> 11/12/2015  15:51               250 test.bat
>                4 File(s)      4,678,262 bytes
>                2 Dir(s)  181,629,882,368 bytes free
>
> C:\test>clang-cl -fms-compatibility-version=19 -Xclang -include-pch
a.h.gch a.cpp
> error: invalid value 'precompiled-header' in '-x precompiled-header'
> error: unable to read PCH file -o: 'no such file or directory'
> error: error reading 'C:\Users\w\AppData\Local\Temp\a-1b7148.obj'
> error: unable to read PCH file -o: 'no such file or directory'
> fatal error: malformed or corrupted AST file: 'Unable to load module
"-o": module file not found'
> 4 errors generated.
>
> C:\test>clang-cl -fms-compatibility-version=19 -Xclang -include-pch a.h
a.cpp

-Xclang passes only the immediately following argument to cc1. You need

clang-cl -fms-compatibility-version=19 -Xclang -include-pch -Xclang a.h.gch
a.cpp

Also, the -Xclang / -cc1 interface is not really supported and has no
stability guarantees; do the cl.exe flags for PCH not work in clang-cl? (If
not, please file a bug on that.)

> error: unable to read PCH file -o: 'no such file or directory'
> fatal error: malformed or corrupted AST file: 'Unable to load module
"-o": module file not found'
> 2 errors generated.
> error: unable to read PCH file -o: 'no such file or directory'
> error: error reading 'C:\Users\w\AppData\Local\Temp\a-5cd097.obj'
> error: unable to read PCH file -o: 'no such file or directory'
> fatal error: malformed or corrupted AST file: 'Unable to load module
"-o": module file not found'
> 4 errors generated.
>
> C:\test>dir
>  Volume in drive C is OS
>  Volume Serial Number is C685-B1F1
>
>  Directory of C:\test
>
> 11/12/2015  15:51    <DIR>          .
> 11/12/2015  15:51    <DIR>          ..
> 11/12/2015  15:45                67 a.cpp
> 11/12/2015  15:44                41 a.h
> 11/12/2015  15:51               250 test.bat
>                3 File(s)            358 bytes
>                2 Dir(s)  181,634,908,160 bytes free
>
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>
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