[cfe-dev] Building Clang on Windows

[Zachary Turner via cfe-dev]

compiler out of heap space is quite interesting.  I can understand the
linker running out of heap space, but the compiler is quite unusual.  The
first thing I would do is check to make sure you are using the 64-bit host
toolchain.  You said you passed -Thost=x64, but let's make sure there's not
a bug in the Visual Studio generator or something.

Turn on Diagnostic output (Tools -> Options -> Projects & Solutions ->
Build and Run -> MSBuild Project Output Verbosity -> Diagnostic) and
rebuild.  Then rebuild and wait for the error to happen.  When it does,
find the error in the log and scroll up looking for "cl.exe" (or do a
reverse find from the end).

Look at the path to cl.exe.  Is it the one from the amd64 directory or the
x86 directory?

If it's running out of heap space on the amd64 native toolchain, it's a bug
in the compiler because this should not even be theoretically possible.  If
it's running out of heap space on the x86 toolchain, then the question is
why isn't it using the correct toolchain.

FWIW, I kind of wish we would stop supporting building with the VS
generator.  MSBuild doesn't really scale well, and now that VS has support
for opening CMake projects directly, and we can build with ninja, I don't
see a strong use case for building with MSBuild anymore given how many
problems it causes.

On Thu, Oct 4, 2018 at 6:24 AM Fábio Picchi via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Updates:
> > Are you building debug or release? If debug, try building release.
> I tried and got the same error.
>
> I noticed my *build target* was *Win32* even though I passed the option
> -Thost=x64 to cmake. I followed the new instructions to regenerate the
> solution using:
> cmake -G "Visual Studio 15 2017" -A x64 -Thost=x64 ..\llvm
>
> Now the build target is displayed as *x64*. I tried to build it in Debug
> mode and still got the dreaded error:
> C1060: compiler is out of heap space
>
> I couldn't check the log errors in detail because I had to leave for work
> but I'll post more updates in the evening.
>
> I will try to do some research on the weekend but it would be great if
> someone could better explain the out of heap space error. How can the
> linker run out of memory just by linking binaries? Why is this process so
> memory intensive? Furthermore, why does it matter if I am targeting x86 or
> x64? I understand the pointers double in size but that would mean more
> memory usage for the x64 target, not the x86.
>
> Thank you very much for the help!
>
> On Thu, Oct 4, 2018 at 4:19 AM Dennis Luehring via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Am 03.10.2018 um 23:29 schrieb Reid Kleckner via cfe-dev:
>> > Can anyone who actually knows answer Shaob's question? He asked "Does
>> the
>> > Win64 generator automatically imply -Thost=x64?
>>
>>
>> CMake gives a warning if not using -Thost=x64 with VS2017 generator
>> Win64 that i could happen that the x86 tool chain is used - so i think
>> its not automatically implied
>>
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