Endianness and SIMD Operations

Endianness refers to the ordering of bytes when integer values are stored out in memory.

• Big-endian: the most significant byte is written to the lowest memory address.

• Little-endian: the least significant byte is written to the lowest memory address.

• Endianness

Endianness and SIMD Bitcasts

Processor endianness has important implications when converting between vector types.

Consider the bitcast operation: %Z = bitcast <4 x i32> %V to <16 x i8>

Ideally, we would like this to be a re-interpret cast in all cases.

But: check the manual page bitcast.

The conversion is done as if the value had been stored to memory and read back as type ty2.

• Using ARM NEON instructions in big endian mode

• Supporting Vector Programming on a Bi-Endian Architecture - LLVM