Panic if AVX or FMA is missing

Our compilation on x86 enables fma and avx in target-feature. We
should panic if the running CPU is actually missing the feature
because otherwise the behavior is undefined and in practice we've
seen segfaults.

The panic will be translated to a Postgres error.

Author: cevian

pgvectorscale/src/access_method/distance.rs

@@ -5,6 +5,13 @@ compile_error!(
     "On x86, the AVX2 feature must be enabled. Set RUSTFLAGS=\"-C target-feature=+avx2,+fma\""
 );
 
+pub fn init() {
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    if (!is_x86_feature_detected!("avx2") || !is_x86_feature_detected!("fma")) {
+        panic!("On x86, pgvectorscale requires the CPU to support AVX2 and FMA. See https://github.com/timescale/pgvectorscale/issues/115");
+    }
+}
+
 #[inline]
 pub fn distance_l2(a: &[f32], b: &[f32]) -> f32 {
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]

pgvectorscale/src/lib.rs

@@ -8,6 +8,7 @@ mod util;
 #[allow(non_snake_case)]
 #[pg_guard]
 pub unsafe extern "C" fn _PG_init() {
+    access_method::distance::init();
     access_method::options::init();
     access_method::guc::init();
 }