GoKawiilIntel SDM documents nonexistent instruction VFMADDRND231PD
A researcher investigating an Intel-documented x86 instruction called vfmaddrnd231pd found it does not actually exist on real hardware. The instruction, which purportedly allowed per-instruction rounding control for fused multiply-add operations, is absent from GNU assembler and lacks corresponding intrinsics in both ICC and Clang, and attempting to execute its hand-assembled opcode on a Haswell CPU triggers an undefined instruction fault.