Heads up: Bug in CMake found when attempting 64-bit build with 32-bit clang-cl.

Hi Nico, Hans, Takumi,

I made it to the bottom of the issue. Turns out that
CMAKE_C_FLAGS=-m64
CMAKE_CXX_FLAGS=-m64
CMAKE_EXE_LINKER_FLAGS=/machine:x64
is enough to do a 64-bit build correctly with a 32-bit clang-cl (i.e. one that targets 32-bit by default). Hooray! The missing piece that I had to track down is why I would see deps = msvc stuff spewing onto my terminal, rather than consumed properly by ninja. I noticed that in rules.ninja, CMake had generated:

msvc_deps_prefix = LINK : error LNK2001:

After some hunting in procmon, I found that there was a call to clang-cl done during the configure process that wasn’t including -m64, leading to a link error. The text of the link error was then being interpreted as a valid output for setting msvc_deps_prefix.

Attached is a quick hack patch for CMake that fixes the issue for me locally. Some more details are in the commit message for the patch. It’s not ideal by any means… my CMake-fu is weak.

Brad, you seem to be roughly our liaison with the CMake community. Do you know what the next steps are for getting this fixed in CMake upstream?

– Sean Silva

0001-Make-sure-to-call-CMAKE_C_COMPILER-with-CMAKE_C_FLAG.patch (2.31 KB)

btw, Hans, Nico: I noticed that we are using a different triple with llvm37_32bit/bin/clang-cl.exe -m64 vs llvm37_64bit/bin/clang-cl.exe.

http://i.imgur.com/eJXf2XN.png

The llvm37_32bit/bin/clang-cl.exe -m64 side of the diff is red; the llvm37_64bit/bin/clang-cl.exe side is in green.

The primary difference seems to be:
llvm37_32bit/bin/clang-cl.exe -m64 chooses -triple x86_64-pc-windows-msvc18.0.0

llvm37_64bit/bin/clang-cl.exe chooses -triple x86_64-w64-windows-msvc18.0.0

Not sure if this is intended behavior or not, but just thought I’d let you guys know, since from what you guys were saying in IRC it sounded like llvm37_32bit/bin/clang-cl.exe -m64 is supposed to be equivalent to llvm37_64bit/bin/clang-cl.exe. Like I said, I managed to get it building with the settings in the OP, so the difference is not a big deal it seems.

– Sean SIlva

The llvm37_32bit/bin/clang-cl.exe -m64 side of the diff is red; the llvm37_64bit/bin/clang-cl.exe side is in green.

The primary difference seems to be:

llvm37_32bit/bin/clang-cl.exe -m64 chooses -triple x86_64-pc-windows-msvc18.0.0

llvm37_64bit/bin/clang-cl.exe chooses -triple x86_64-w64-windows-msvc18.0.0

Not sure if this is intended behavior or not, but just thought I’d let you guys know,

since from what you guys were saying in IRC it sounded like llvm37_32bit/bin/clang-cl.exe -m64

is supposed to be equivalent to llvm37_64bit/bin/clang-cl.exe. Like I said, I managed to get it

building with the settings in the OP, so the difference is not a big deal it seems.

What’s the default triple for llvm37_32bit/bin/clang-cl.exe? –m64 strips the CPU/Arch part of the triple and replaces it with ‘x86_64’ so I expect the 32-bit triple is something like i586-pc-windows-msvc18.0.0.

I don’t see any references to Triple::PC (aside from TripleTest.cpp) and ‘w64’ looks like it parses as Triple::UnknownVendor so it doesn’t seem to make any functional difference to most of the LLVM projects. Is anyone aware of functional differences between the ‘pc’ and ‘w64’ vendors in other toolchains?

This looks like the same problem reported here:

CMakeClDeps.cmake doesn't work if CC contains arguments
http://www.cmake.org/Bug/view.php?id=15596

I've just drafted some changes to fix it. Please follow the issue
tracker entry for details. Also please try out the fix and report
back.

Thanks,
-Brad

As Daniel says, this is probably benign, but it looks confusing.
r248005 should fix.

> The `llvm37_32bit/bin/clang-cl.exe -m64` side of the diff is red; the
`llvm37_64bit/bin/clang-cl.exe` side is in green.

> The primary difference seems to be:

> `llvm37_32bit/bin/clang-cl.exe -m64` chooses `-triple
x86_64-pc-windows-msvc18.0.0`

> `llvm37_64bit/bin/clang-cl.exe` chooses `-triple
x86_64-w64-windows-msvc18.0.0`

>

> Not sure if this is intended behavior or not, but just thought I'd let
you guys know,

> since from what you guys were saying in IRC it sounded like
`llvm37_32bit/bin/clang-cl.exe -m64`

> is supposed to be equivalent to `llvm37_64bit/bin/clang-cl.exe`. Like I
said, I managed to get it

> building with the settings in the OP, so the difference is not a big
deal it seems.

What's the default triple for llvm37_32bit/bin/clang-cl.exe? –m64 strips
the CPU/Arch part of the triple and replaces it with 'x86_64' so I expect
the 32-bit triple is something like i586-pc-windows-msvc18.0.0.

Yeah, it is i686-pc-windows-msvc18.0.0

-- Sean Silva

> msvc_deps_prefix = LINK : error LNK2001:
>
> there was a call to clang-cl done during the configure process
> that *wasn't including -m64*

This looks like the same problem reported here:

CMakeClDeps.cmake doesn't work if CC contains arguments
http://www.cmake.org/Bug/view.php?id=15596

D'oh, I should have googled for `msvc_deps_prefix = LINK : error LNK2001: `!

I've just drafted some changes to fix it. Please follow the issue
tracker entry for details. Also please try out the fix and report
back.

I just tried with the `next` branch and it works! Thanks!

-- Sean Silva