Fixed-point load and store with update instructions

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Load and store instructions have an update form, in which the base GPR is updated with the EA in addition to the regular move of information from or to memory.

Load and store instructions have an "update" form, in which the base GPR is updated with the EA in addition to the regular move of information from or to memory.

For POWER® family load instructions, there are four conditions which result in the EA not being saved in the base GPR:

  1. The GPR to be updated is the same as the target GPR. In this case, the updated register contains data loaded from memory.
  2. The GPR to be updated is GPR 0.
  3. The storage access causes an alignment interrupt.
  4. The storage access causes a data storage interrupt.

For POWER® family store instructions, conditions 2, 3, and 4 result in the EA not being saved into the base GPR.

For PowerPC® load and store instructions, conditions 1 and 2 above result in an invalid instruction form.

In user programs, load and store with update instructions which access an unaligned data location will be performed by either the hardware or the alignment interrupt handler of the underlying operating system. An alignment interrupt will result in the EA not being in the base GPR.