[Mesa-dev] [PATCH 2/9] gallivm: Use LLVMSetTarget.

[Jose Fonseca]

On 18/04/16 13:27, Emil Velikov wrote:
> Hi Jose,
>
> On 18 April 2016 at 10:14, Jose Fonseca <jfonseca at vmware.com> wrote:
>> Instead of LLVM C++ interfaces.
>> ---
>>   src/gallium/auxiliary/gallivm/lp_bld_misc.cpp | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
>> index c1e262b..37e2f08 100644
>> --- a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
>> +++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
>> @@ -519,9 +519,11 @@ lp_build_create_jit_compiler_for_module(LLVMExecutionEngineRef *OutJIT,
>>          /*
>>           * MCJIT works on Windows, but currently only through ELF object format.
>>           */
>> -       std::string targetTriple = llvm::sys::getProcessTriple();
>> -       targetTriple.append("-elf");
>> -       unwrap(M)->setTargetTriple(targetTriple);
>> +#  ifdef _WIN64
>> +       LLVMSetTarget(M, "x86_64-pc-win32-elf");
>> +#  else
>> +       LLVMSetTarget(M, "i686-pc-win32-elf");
>> +#  endif
>
> I've noticed that you're using LLVM_HOST_TRIPLE in patch 7/9. Wouldn't
> it be better to use it here as well ?
>
> +       LLVMSetTarget(M, LLVM_HOST_TRIPLE "-elf");

Thanks for taking a look.

It's a good remark.

Surprisingly LLVM uses different LLVM_HOST_TRIPLE for MinGW/MSVC:

$ grep LLVM_HOST_TRIPLE */llvm-*/include
mingw32/llvm-3.3.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"i686-pc-mingw32"
mingw32/llvm-3.4.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"i686-pc-mingw32"
mingw64/llvm-3.3.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"x86_64-w64-mingw32"
mingw64/llvm-3.4.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"x86_64-w64-mingw32"
msvc32/llvm-3.3.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"i686-pc-win32"
msvc32/llvm-3.4.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"i686-pc-win32"
msvc64/llvm-3.3.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"x86_64-pc-win32"
msvc64/llvm-3.4.1/include/llvm/Config/config.h:#define LLVM_HOST_TRIPLE 
"x86_64-pc-win32"

I'm not sure if this will matter (ie, will make LLVM behave internally 
slightly differently, using slightly different conventions), but I 
rather not take any chances and have MinGW match MSVC, for good or bad.

I'll add a comment explaining this though.  (And I should find a way to 
achieve the same on the old-JIT path too.)

> That aside I'm really glad to see mesa (modulo swr) no longer using
> the unstable LLVM C++ API.

Still not quite there, but yes that's indeed the hope.

 > Perhaps at some point we could port these
> to normal C and make gallivm 'C++ free'  ;-)

There's no much use of C++ left indeed, and at some point might as well 
remove it completely.

Would this make gallivm/LLVM more appealing to Intel?

There's a lot of places in Mesa where JIT makes sense.  Particularly 
format conversion, where the space of 
src-format/dest-format/cpu-capabilities is huge, and it's all 
performance sensitive.   Though I suppose with Vulkan that should rarely 
be needed.


For my part, my personal goal is to eliminate 
src/gallium/auxiliary/rtasm in the medium term.  And I think should 
remove src/mesa/x86/rtasm too.


Jose