[FP16] Implement load and store instructions.

[brendandahl]

Specified at https://github.com/WebAssembly/half-precision/blob/main/proposals/half-precision/Overview.md

[brendandahl]

I for some reason thought we used LLVM to build everywhere. I'll need to come up with some that that works for gcc/msvc.

[tlively]

Nice, looks good besides the build issues with the interpreter.

[kripken]

This will be the first non-Apache2-licensed code (that is not testing code), so it might be worth a mention in our toplevel LICENSE file.

Any chance there's an Apache2-licensed alternative?

[tlively]

We could also reach out to Marat and ask if he's willing and able to dual-license it.

[brendandahl]

A quick search didn't find any apache license libraries, only another MIT one. IANAL, but I was under the impression MIT is fine to include in apache.

[kripken]

Yeah, I don't think it's a blocker to use this code, it is compatible AFAIU. But it is a different license so it seems worth mentioning at the top level.

[brendandahl]

Hmm...looks like the FP16 library is having issues with MSVC still.

[brendandahl]

I've opened Maratyszcza/FP16#31 for MSVC issue.

[osa1]

It looks like the conditionals in bitcasts.h are not working on some compiler/targets, I get these errors when building on Dart's Windows builders:

../../third_party/binaryen/src/third_party/FP16/include/fp16/bitcasts.h(26,9): error: use of undeclared identifier '_castu32_f32'
   26 |         return _castu32_f32(w);
      |                ^
../../third_party/binaryen/src/third_party/FP16/include/fp16/bitcasts.h(44,9): error: use of undeclared identifier '_castf32_u32'
   44 |         return _castf32_u32(f);
      |                ^
../../third_party/binaryen/src/third_party/FP16/include/fp16/bitcasts.h(62,9): error: use of undeclared identifier '_castu64_f64'
   62 |         return _castu64_f64(w);
      |                ^
../../third_party/binaryen/src/third_party/FP16/include/fp16/bitcasts.h(80,9): error: use of undeclared identifier '_castf64_u64'
   80 |         return _castf64_u64(f);
      |                ^
Note: including file:      ../../third_party/binaryen/src/third_party/FP16/include/fp16/macros.h

The logs don't include the compiler version, I'm trying to find the compiler used in this build. I will update.

[brendandahl]

@osa1 were you able to find what compiler version you are using?

[osa1]

@brendandahl version 19.

[mkustermann]

../../third_party/binaryen/src/third_party/FP16/include/fp16/bitcasts.h(26,9): error: use of undeclared identifier
'_castu32_f32'
26 | return _castu32_f32(w);

Binaryen seems to include immintrin.h in binaryen/third_party/FP16/include/fp16/bitcasts.h

#if defined(__INTEL_COMPILER) || defined(_MSC_VER) && (_MSC_VER >= 1932) && (defined(_M_IX86) || defined(_M_X64))
	#include <immintrin.h>
#endif

#if defined(_MSC_VER) && !defined(__clang__) && (defined(_M_ARM) || defined(_M_ARM64))
	#include <intrin.h>
#endif

static inline float fp32_from_bits(uint32_t w) {
  ...
#elif defined(__INTEL_COMPILER) || defined(_MSC_VER) && (_MSC_VER >= 1932) && (defined(_M_IX86) || defined(_M_X64))
	return _castu32_f32(w);   // <-- COMPILATION ERROR, _castu32_f32 not found.
...
#endif
}

(side note: Clang windows compiler will define _MSC_VER variables)

The clang windows compiler seems to ship this function

• in llvm-project/clang/lib/Headers/ia32intrin.h
• which is included in llvm-project/clang/lib/Headers/x86intrin.h (which also #include <immintrin.h>s)
• which is included in llvm-project/clang/lib/Headers/intrin.h

=> So I think the conditional include should be fixed to #include <intrin.h> instead of #include <immintrin.h>