Special registers in the PowerPC®

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The Special-Purpose Register Conventions shows thet PowerPC® special purpose registers (SPRs).

The Special-Purpose Register Conventions table shows the PowerPC® special purpose registers (SPRs). These are the only SPRs for which there is a register convention.

Table 1. Special-Purpose Register Conventions
Register or Register Field Status Use
LR volatile Used as a branch target address or holds a return address.
CTR volatile Used for loop count decrement and branching.
XER volatile Fixed-point exception register.
FPSCR volatile Floating-point exception register.
CR0, CR1 volatile Condition-register bits.
CR2, CR3, CR4 nonvolatile Condition-register bits.
CR5, CR6, CR7 volatile Condition-register bits.

Routines that alter CR2, CR3, and CR4 must save and restore at least these fields of the CR. Use of other CR fields does not require saving or restoring.