Agner`s CPU blog

Software optimization resources | E-mail subscription to this blog | www.agner.org

Proposal for an ideal extensible instruction set
Author: Agner Date: 2016-03-10 04:51
Joe Duarte wrote:
why 32 registers?
Thanks for the references. The article by Alipour seems to be about the physical register file used for renaming, not the number of logical registers.

If the compiler can do global register allocation then it can avoid spilling registers to memory when function1 calls function2 by using different registers in the two functions. The more registers we have, the deeper levels of nested function calls can we have without spilling registers to memory. But we should not forget that a typical program uses more than 99% of its execution time in the innermost loop. The innermost loop should not have more than at most 2 - 3 levels of function nesting in a well designed program. Register spilling outside the innermost loop is pretty irrelevant for performance. If we assume that each function uses a handful of registers and that some of these are used for short-lived variables that do not need to be saved across a function call, then the optimal number of registers might be something like 16.

If a typical instruction code has three register fields then we will need to use three more bits of instruction code for each time the number of registers is doubled. With 32 registers and three register fields, we will use 15 bits of the 32-bit code word only for specifying register operands.

The proposed register set includes vector registers of variable size, and the size may grow indefinitely in future implementations. Saving and restoring a vector register with variable size is quite complicated. First, you have to detect the maximum vector size, and then you have to allocate a corresponding space on the stack. It is good to have many vector registers in order to minimize the need for this procedure. Therefore, I think that 32 vector registers is reasonable. It will be difficult to extend the number of register in the future if the need should arise, so it is better to settle for too many than too few.

The number of scalar registers may be the same because scalar and vector instructions should be coded in the same way, according to my proposal.

 
thread Proposal for an ideal extensible instruction set new - Agner - 2015-12-27
replythread Itanium new - Ethan - 2015-12-28
last reply Itanium new - Agner - 2015-12-28
replythread Proposal for an ideal extensible instruction set new - hagbardCeline - 2015-12-28
last replythread Proposal for an ideal extensible instruction set new - Agner - 2015-12-28
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
replythread Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-05
replythread Proposal for an ideal extensible instruction set new - John D. McCalpin - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-06
last reply Proposal for an ideal extensible instruction set new - Ook - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - acppcoder - 2016-03-27
reply Proposal for an ideal extensible instruction set new - Jake Stine - 2016-01-11
replythread Proposal for an ideal extensible instruction set new - Agner - 2016-01-12
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-02
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-03
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-12
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-18
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-21
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-22
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-23
replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-23
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last replythread Proposal for an ideal extensible instruction set new - asdf - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-25
replythread limit instruction length to power of 2 new - A-11 - 2016-02-24
last replythread limit instruction length to power of 2 new - Agner - 2016-02-24
replythread Any techniques for more than 2 loads per cycle? new - Hubert Lamontagne - 2016-02-24
last reply Any techniques for more than 2 loads per cycle? new - Agner - 2016-02-25
last replythread limit instruction length to power of 2 new - A-11 - 2016-02-25
last reply limit instruction length to power of 2 new - Hubert Lamontagne - 2016-02-25
replythread More ideas new - Agner - 2016-03-04
replythread More ideas new - Hubert Lamontagne - 2016-03-07
last reply More ideas new - Agner - 2016-03-08
last reply More ideas new - Agner - 2016-03-09
replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-07
reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-09
last replythread Proposal for an ideal extensible instruction set - Agner - 2016-03-10
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - anon2718 - 2016-03-13
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-14
replythread A design without a TLB new - Agner - 2016-03-11
replythread A design without a TLB new - Hubert Lamontagne - 2016-03-11
reply A design without a TLB new - Agner - 2016-03-11
last reply A design without a TLB new - Agner - 2016-03-12
reply A design without a TLB new - Bigos - 2016-03-13
last reply A design without a TLB new - Agner - 2016-03-28
replythread Proposal now published new - Agner - 2016-03-22
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-23
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-25
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-28
last replythread Proposal now published new - Agner - 2016-03-29
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-30
last replythread Proposal now published new - Agner - 2016-03-30
last replythread Do we need instructions with two outputs? new - Agner - 2016-03-31
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-01
reply Do we need instructions with two outputs? new - Agner - 2016-04-01
replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-03
reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-03
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-03
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-04
reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-04
last replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-06
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-07
last replythread Do we need instructions with two outputs? new - HarryDev - 2016-04-08
last reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-09
replythread How about stack machine ISA? new - A-11 - 2016-04-10
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-14
last replythread treating stack ISA as CISC architecure new - Agner - 2016-04-14
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-17
replythread treating stack ISA as CISC architecure new - Hubert Lamontagne - 2016-04-17
last replythread stack ISA versus long vectors new - Agner - 2016-04-18
last replythread stack ISA versus long vectors new - Hubert Lamontagne - 2016-04-19
last reply stack ISA versus long vectors new - Agner - 2016-04-20
last reply treating stack ISA as CISC architecure new - A-11 - 2016-04-18
replythread Proposal for an ideal extensible instruction set new - zboson - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-12
last reply Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-12
replythread Version 1.01 new - Agner - 2016-05-10
last replythread Version 1.01 new - Hubert Lamontagne - 2016-05-13
last replythread Version 1.01 new - Agner - 2016-05-14
last replythread Version 1.01 new - Harry - 2016-06-02
replythread Public repository new - Agner - 2016-06-02
reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Agner - 2016-06-09
replythread Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects new - cv - 2016-05-20
last reply Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects new - Peter Cordes - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Agner - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Joe Duarte - 2016-06-17
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-18
last reply Rethinking DLLs and shared objects new - Bigos - 2016-06-18
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-02
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-04
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-04
last reply Rethinking DLLs and shared objects new - Agner - 2016-06-06
replythread Is it better to have two stacks? new - Agner - 2016-06-05
reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-07
replythread Is it better to have two stacks? new - Eden Segal - 2016-06-13
last replythread Is it better to have two stacks? new - Agner - 2016-06-13
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-14
last replythread Is it better to have two stacks? new - Agner - 2016-06-14
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-15
last replythread Is it better to have two stacks? new - Agner - 2016-06-15
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-16
last replythread Is it better to have two stacks? new - Agner - 2016-06-16
last reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-17
last reply Is it better to have two stacks? new - Freddie Witherden - 2016-06-22
last reply Now on Github new - Agner - 2016-06-26