[llvm-dev] `_m_prefetchw` type signature mismatch on Windows

[Rickard Andersson via llvm-dev]

Hi again,

It turns out I was mistaken about the source of the error. I've made a 
paste with the error I'm running into instead; it comes from a 
redeclaration (still in a Windows header, but in one of the Windows 
Kits):

https://bpa.st/5PSA

`sqlite3.c` includes `windows.h` and it seems that perhaps there is an 
IFDEF lacking somewhere that causes `winnt.h` to redeclare 
`_m_prefetchw`.

Is it in the scope of clang/LLVM to address this?

// Rickard

------ Original Message ------
From: "Eli Friedman" <efriedma at quicinc.com>
To: "Rickard Andersson" <gonz at severnatazvezda.com>; 
"llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>
Sent: 2020-06-11 21:49:20
Subject: RE: [llvm-dev] `_m_prefetchw` type signature mismatch on 
Windows

>If clang is finding MSVC's mm3dnow.h instead of its own, you've misconfigured the include paths.  clang should always use its own version.
>
>-Eli
>
>>  -----Original Message-----
>>  From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Rickard
>>  Andersson via llvm-dev
>>  Sent: Thursday, June 11, 2020 6:15 AM
>>  To: llvm-dev at lists.llvm.org
>>  Subject: [EXT] [llvm-dev] `_m_prefetchw` type signature mismatch on
>>  Windows
>>
>>  Hi,
>>
>>  I was compiling `sqlite3.c` via Zig a while ago and noticed a type
>>  mismatch between the Windows headers and the LLVM headers that Zig
>>  ships
>>  with.
>>
>>  The Windows header `mm3dnow.h` declares it as:
>>
>>       void _m_prefetchw(volatile const void*_Source);
>>
>>  Whereas the LLVM header `clang\lib\Headers\prfchwintrin.h` declares:
>>
>>       static __inline__ void __attribute__((__always_inline__,
>>  __nodebug__))
>>       _m_prefetchw(volatile const void *__P) {
>>         __builtin_prefetch (__P, 1, 3 /* _MM_HINT_T0 */);
>>       }
>>
>>  `__builtin_prefetch`, which `_m_prefetchw` is using, is defined as
>>  taking `const void*` at the moment.
>>
>>  The mismatch effectively causes the function to have two different
>>  signatures when compiling C source in Zig on Windows. The most direct
>>  change is to modify the shipped Zig headers, but it'd be interesting to
>>  see this fixed at the source.
>>
>>  Is there any major issue with `ifdef`ing a solution when using MSVC that
>>  anyone can see?
>>
>>  With regards,
>>  Rickard Andersson
>>
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