Annotate platform specific hardware intrinsics with the ConstExpected attribute #80192
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Tagging subscribers to this area: @dotnet/area-system-runtime-intrinsics Issue Detailsnull
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| @@ -51,25 +51,25 @@ public abstract class AdvSimd : ArmBase | |||
| // /// float32x2_t vmla_lane_f32 (float32x2_t a, float32x2_t b, float32x2_t v, const int lane) | |||
| // /// A32: VMLA.F32 Dd, Dn, Dm[lane] | |||
| // /// </summary> | |||
| // public static Vector64<float> MultiplyAddBySelectedScalar(Vector64<float> addend, Vector64<float> left, Vector64<float> right, byte rightIndex) => MultiplyAddBySelectedScalar(addend, left, right, rightIndex); | |||
| // public static Vector64<float> MultiplyAddBySelectedScalar(Vector64<float> addend, Vector64<float> left, Vector64<float> right, [ConstantExpected(Max = (byte)(1))] byte rightIndex) => MultiplyAddBySelectedScalar(addend, left, right, rightIndex); | |||
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Arm64 and WASM expect values to be exactly in range. As such, we strictly limit the input between 0 and Max or 1 and Max.
The exact semantics is dependent on the instruction and is table driven in the JIT: https://github.com/dotnet/runtime/blob/main/src/coreclr/jit/hwintrinsicarm64.cpp#L215-L271
| @@ -398,61 +399,61 @@ public new abstract class X64 : Sse42.X64 | |||
| /// __m128i _mm256_extractf128_si256 (__m256i a, const int imm8) | |||
| /// VEXTRACTF128 xmm/m128, ymm, imm8 | |||
| /// </summary> | |||
| public static Vector128<byte> ExtractVector128(Vector256<byte> value, byte index) => ExtractVector128(value, index); | |||
| public static Vector128<byte> ExtractVector128(Vector256<byte> value, [ConstantExpected] byte index) => ExtractVector128(value, index); | |||
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x86/x64 on the other hand typically allows any input and will mask off to only the bits needed.
There are a couple exceptions, but it is also table driven on the JIT side: https://github.com/dotnet/runtime/blob/main/src/coreclr/jit/hwintrinsicxarch.cpp#L196-L230
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| /// <summary> | ||
| /// __m128i _mm_i32gather_epi32 (int const* base_addr, __m128i vindex, const int scale) | ||
| /// VPGATHERDD xmm, vm32x, xmm | ||
| /// The scale parameter should be 1, 2, 4 or 8, otherwise, ArgumentOutOfRangeException will be thrown. | ||
| /// </summary> | ||
| public static unsafe Vector128<int> GatherVector128(int* baseAddress, Vector128<int> index, byte scale) | ||
| public static unsafe Vector128<int> GatherVector128(int* baseAddress, Vector128<int> index, [ConstantExpected(Min = (byte)(1), Max = (byte)(8))] byte scale) |
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The one particularly interesting case for x86/x64 is GatherVector and GatherMaskVector. These take exactly 1, 2, 4, or 8 with other values being disallowed.
This is most closely modeled on the attribute by restricting to between 1 and 8 inclusive.
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I wrote a small program that added them.
The existing JIT conditions, which were originally seeded from the Architecture Manuals
Manual validation in VS that the analyzer gets triggered |
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This seems to be breaking some wasm builds - https://dev.azure.com/dnceng-public/public/_build/results?buildId=127536&view=logs&jobId=63c2d0c8-fec2-5788-81c8-f3ac95e8841f&j=1edeb425-f545-5bac-61ef-500e115ab70f&t=34633226-1964-5e2b-9141-b7baebe1e47c . The changes in #80271 are unrelated as they come into effect when running tests. |
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The fix is easy, but I'm unsure why it didn't trigger these failures in the PR. |
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Fix is here: #80282 |
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The xplat intrinsics do not need this as they use alternative instruction sequences and handling where possible. They do not need to fallback to anything like a jump table.