Here's a list of my requirements:
1. Built-in types for floating point and integer vectors (compile time constant width). E.g. float32x4_t or int64x2_t. Maybe have some matrix types too.
2. Normal infix operators for arithmetic (+, -, /). You can do this with C [1]. Built-in syntax for vector shuffles (can't do this in C) [2].
3. Compile time polymorphism to make vector-width agnostic code. If you write sin4f and sin8f (in C), they are line-by-line identical except for types. You should be able to write a single sin() function that works for any vector width
4. A standard library that has all the usual libm math functions (sin, cos, log, exp, asin, atanh, etc). I could do with less-than-perfect precision for performance (at least if -ffast-math is enabled)
5. A standard library for some basic vector and matrix operations for static-sized vectors and matrices. E.g. dot product, matrixmatrix product, matrixvector product, inverse matrix, etc.
I put some hope on Rust, which has been working on some SIMD stuff. But the current iteration doesn't fulfill most of my requirements.
[0] https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html
[1] You can do this:
typedef float float32x4_t __attribute__((vector_size(16)));
float32x4_t a = { 1, 2, 3, 4 }, b = { 5, 6, 7, 8 }, c = (a+b)*(a-b);