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simd.md

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SIMD in flambda2

Vector types

Intrinsics

Load/Store

Unlike intrinsics, SIMD loads and stores are represented as flambda2-visible primitives.

  • string, bytes: caml_{string,bytes}_{getu128,setu128}{u} map to MOVUPD, an unaligned 128-bit vector load/store. The primitives can operate on all 128-bit vector types. The safe primitives raise Invalid_argument if any part of the vector is not within the array bounds; the u suffix omits this check. Aligned load/store is not available because these values may be moved by the GC.

  • bigstring: caml_bigstring_{get,set}{u}128{u} map to MOVAPD or MOVUPD. The primitives can operate on all 128-bit vector types. The prefix u indicates an unaligned operation (MOVUPD), and the suffix u omits bounds checking. Aligned load/store is available because bigstrings are allocated by malloc.

  • float array, floatarray, float# array: the corresponding primitives take an index in floats and are required to operate on float64x2s. The address is computed as array + index * 8; the safe primitives bounds-check against 0, length - 1. The primitives on float array are only available when the float array optimization is enabled. Aligned load/store is not available because these values may be moved by the GC.

  • nativeint# array, int64# array: the corresponding primitives take an index in nativeints/int64s and are required to operate on int64x2s. The address is computed as array + index * 8; the safe primitives bounds-check against 0, length - 1. The primitives on nativeint# array are only available in 64-bit mode. Aligned load/store is not available because these values may be moved by the GC.

  • int32# array: the corresponding primitives take an index in int32s and are required to operate on int32x4s. The address is computed as array + index * 4; the safe primitives bounds-check against 0, length - 3. Aligned load/store is not available because these values may be moved by the GC.

  • %immediate64 array: the corresponding primitives take an index in immediates, and are required to operate on int64x2s. The primitives can operate on all ('a : immediate64) arrays and are only available in 64-bit mode. The address is computed as array + index * 8; the safe primitives bounds-check against 0, length - 1. Aligned load/store is not available because these values may be moved by the GC. Load/store directly reads/writes two 64-bit tagged values. The "safe" primitives do not check for proper tagging, so are not to be exposed to users as "safe."