The next question is where did I get the details above. The GCC documentation for __builtin_ia32_loadupd provides minimal information (the builtin name, parameters and return types). Not very informative. Looking up the Intel intrinsic description is more informative. You can Google the intrinsic name or use the Intel Intrinsic guide for this. The Intrinsic Guide is interactive and includes  Intel (Chip) technology and text based search capabilities. Clicking on the intrinsic name opens to a synopsis including; the underlying instruction name, text description, operation pseudo code, and in some cases performance information (latency and throughput). The key is to get a description of the intrinsic (operand fields and types, and which fields are updated for the result) and the underlying Intel instruction. If the Intrinsic guide is not clear you can look up the instruction details in the “Intel® 64 and IA-32 Architectures Software Developer’s Manual”. Information about the PowerISA vector facilities is found in the PowerISA Version 2.07B (for POWER8 and 3.0 for POWER9) manual, Book I, Chapter 6. Vector Facility and Chapter 7. Vector-Scalar Floating-Point Operations. Another good reference is the OpenPOWER ELF V2 application binary interface (ABI) document, Chapter 6. Vector Programming Interfaces and Appendix A. Predefined Functions for Vector Programming. Another useful document is the original Altivec Technology Programmers Interface Manual with a user friendly structure and many helpful diagrams. But alas the PIM does does not cover the recent PowerISA (power7,  power8, and power9) enhancements.