Fix vector's Narrow intrinsics

[radekdoulik]

The BCL Vector classes have non-saturating Narrow methods, while wasm instructions are saturating. AFAIK wasm does not have non-saturating narrow instructions. So instead of

i8x16.narrow_i16x8_s
i8x16.narrow_i16x8_u
i16x8.narrow_i32x4_s
i16x8.narrow_i32x4_u

use v8x16.shuffle instruction to implement the extract narrow operation.

This fixes System.Numerics.Tests.GenericVectorTests.Narrow[U]Int* tests.

[radekdoulik]

Example of emitted code:

> wa-info.exe -d -f Narrow.*16 dotnet.wasm
  ...
  local.get $2
  local.get $2
  v128.load offset:80 align:4    [SIMD]
  local.get $2
  v128.load offset:96 align:4    [SIMD]
  i8x16.shuffle 0x1e1c1a18161412100e0c0a0806040200    [SIMD]
  v128.store offset:112 align:4    [SIMD]
  ...

[tannergooding]

Worth noting that saturating narrow is coming: #75724

So might be worth keeping the logic easily accessible so we can turn it back on when the new APIs are added.

[EgorBo]

@radekdoulik what is the easiest option to check codegen/LLVM IR for a SIMD operation in WASM? I assume I need to use one of the WASM samples but how/where do I specify MONO_VERBOSE_METHOD ?

[radekdoulik]

@radekdoulik what is the easiest option to check codegen/LLVM IR for a SIMD operation in WASM? I assume I need to use one of the WASM samples but how/where do I specify MONO_VERBOSE_METHOD ?

I usually use llvm-dis on .bc files. Sometime I call mono aot crosscompiler by hand and then it should be possible to use MONO_VERBOSE_METHOD.

For checking generated wasm code I use wa-info -d -f .... https://github.com/radekdoulik/wa-info#installation

[EgorBo]

@radekdoulik what is the easiest option to check codegen/LLVM IR for a SIMD operation in WASM? I assume I need to use one of the WASM samples but how/where do I specify MONO_VERBOSE_METHOD ?

I usually use llvm-dis on .bc files. Sometime I call mono aot crosscompiler by hand and then it should be possible to use MONO_VERBOSE_METHOD.

For checking generated wasm code I use wa-info -d -f .... https://github.com/radekdoulik/wa-info#installation

which sample would you recommend to use for that?

[vargaz]

The easiest is probably src/mono/samples/wasm/console-v8.
Build it using make AOT=1
The .bc files are in
artifacts/obj/mono/Wasm.Console.V8.Sample/wasm/Release/browser-wasm/wasm/for-publish/.

[vargaz]

If you want to run the cross compiler by hand, build the sample using:
make AOT=1 MSBUILD_ARGS="/v:d"
then grep MONO_PATH in the output to find the cross compiler invocations.

[radekdoulik]

The failing build is #81859