Editing Pentium Pro (section)

===Instruction set===

The Pentium Pro (P6) introduced new 'conditional move' instructions into the Intel range; the <code>CMOV''cc''</code> and <code>FCMOV''cc''</code> (‘conditional move’) instructions fetch a source value from a register or memory, and optionally write that value to a destination register according to a condition ''cc''  on the flags register, the same conditions used by the conditional jump (<code>J''cc''</code>) instructions. For example, <code>CMOVNE</code> moves a specified value into a register if the flags register matches the NE (not-equal) condition, i.e. the [[zero flag]] is unset.  If the zero flag is set, the condition in false, and the destination register keeps its value.  This allows simple if-then-else operations (such as commonly used by the [[Ternary conditional operator|<code>? :</code> operation]] in [[C (programming language)|C]]) without a costly conditional branch.  The <code>FCMOV''cc''</code> variant provides the same functionality for floating-point registers.  Unfortunately, <code>CMOV</code> does not support immediate (in-line constant) source values nor memory destinations.

A second development was the documentation of the <code>UD2</code> illegal instruction. This op code is reserved and guaranteed to cause an illegal instruction exception on the P6 and all later processors. This allows developers to easily crash the current program in a future-proof fashion when a bug is detected by software.