Agner`s CPU blog

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

Merging with first operand
Author: Sylvain Collange Date: 2016-08-18 10:20
Agner wrote:
Can you bypass a result to multiple in-flight instructions using the same bus? If so, you need only few bypass buses.
Yes, that is essentially how it is done (or at least how it is described in textbooks). But the load on the bus increases with the number of potential consumers, and so do area, delay and power.
There are still a lot of tricks hardware designers can use on a given technology, but the general trends hold anyway. And as far as instruction set design is concerned, general trends are what we care about.

Do you have any references on how the register read ports are designed and why they are so expensive?
Rixner et al., Register Organization for Media Processing, HPCA 2000.
www.ai.mit.edu/projects/aries/papers/imagine/register.pdf
evaluates the tradeoffs using analytical models and considers various distributed and SIMD RF organizations.

Do you have code examples showing how a compiler can perform if-conversion from some arbitrary code?
A branch in a vectorized loop is translated to a mask. All the good compilers can do this today.
I was asking specifically in the context of ForwardCom and the choice of the first operand as the masked source.
e.g. Which code is generated when you vectorize :
for all i {
  int x = a[i];
  int y = b[i];
  if(x > y) {
    y = x + 1;
  }
  c[i] = y;
  d[i] = x;
}
The translation in a classic predicated ISA is straighforward, but what about in ForwardCom?
I have the impression that the first operand of the masked instructions will end up being the same as the destination anyway, and that we need an extra register move.

That was not my plan, but of course such an instruction could be defined if there is a need for it. But why would you have a conditional inside a polynomial?
I do not know, but the question is what a compiler will emit when vectorizing such a program if the instruction does not exist? (And the compiler has to assume that arithmetic exceptions might be enabled.)
 
thread Proposal for instruction set - now on Github new - Agner - 2016-06-26
replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-07-04
last replythread Proposal for instruction set - now on Github new - Agner - 2016-07-04
replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-07-06
last replythread Proposal for instruction set - now on Github new - Agner - 2016-07-06
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-07-07
last reply Proposal for instruction set - now on Github new - Agner - 2016-07-07
replythread Whole-function vectorization and conditionals new - Sylvain Collange - 2016-08-15
last replythread Whole-function vectorization and conditionals new - Agner - 2016-08-15
last replythread Whole-function vectorization and conditionals new - Sylvain Collange - 2016-08-15
last replythread Whole-function vectorization and conditionals new - Agner - 2016-08-15
last replythread Whole-function vectorization and conditionals new - Sylvain Collange - 2016-08-15
last replythread Whole-function vectorization and conditionals new - Agner - 2016-08-15
reply Number of input dependencies new - Agner - 2016-08-16
last replythread Whole-function vectorization and conditionals new - Sylvain Collange - 2016-08-16
last replythread Whole-function vectorization and conditionals new - Agner - 2016-08-17
last replythread Merging with first operand - Sylvain Collange - 2016-08-18
last replythread Merging with first operand new - Agner - 2016-08-19
replythread SIMD exceptions are fine with masking new - Sylvain Collange - 2016-08-19
last replythread SIMD exceptions are fine with masking new - Agner - 2016-08-20
reply SIMD exceptions are fine with masking new - Hubert Lamontagne - 2016-08-20
last reply SIMD exceptions are fine with masking new - Sylvain Collange - 2016-08-25
last reply Merging with first operand new - Hubert Lamontagne - 2016-08-19
last replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-08-17
last replythread Proposal for instruction set - now on Github new - Agner - 2016-08-18
last replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-08-31
reply Proposal for instruction set - now on Github new - Agner - 2016-08-31
last reply Proposal for instruction set - now on Github new - Jorcy Neto - 2016-09-01
replythread Proposal for instruction set - now on Github new - Yuhong Bao - 2016-07-12
last reply Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-07-12
replythread Things from MIPS (and novel things) new - Anonymous - 2016-07-28
replythread Things from MIPS (and novel things) new - Agner - 2016-07-28
last reply Things from MIPS (and novel things) new - Hubert Lamontagne - 2016-07-28
last replythread Matrix multiplication new - Agner - 2016-07-29
reply Matrix multiplication new - Hubert Lamontagne - 2016-07-29
last replythread Matrix multiplication new - John D. McCalpin - 2016-07-29
last reply Matrix multiplication new - Agner - 2016-07-29
replythread Introduction website new - Agner - 2016-08-01
last replythread Introduction website new - EricTL - 2017-07-17
last replythread Introduction website new - Agner - 2017-07-18
last replythread Introduction website new - EricTL - 2017-07-20
last reply Introduction website new - Agner - 2017-07-20
replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-08-04
last replythread Proposal for instruction set - now on Github new - Agner - 2016-08-04
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-08-05
replythread Proposal for instruction set - now on Github new - Agner - 2016-08-06
last replythread Proposal for instruction set - now on Github new - fanoI - 2016-08-08
last replythread Proposal for instruction set - now on Github new - Agner - 2016-08-08
last reply Proposal for instruction set - now on Github new - fanoI - 2016-08-09
last replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-08-08
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-08-09
last replythread Proposal for instruction set - now on Github new - Joe Duarte - 2016-08-11
last replythread Proposal for instruction set - now on Github new - Agner - 2016-08-12
last reply Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-08-12
replythread Proposal for instruction set - now on Github new - grant galitz - 2016-08-22
reply Proposal for instruction set - now on Github new - Agner - 2016-08-22
last reply Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-08-24
replythread ARM with scalable vector extensions new - Agner - 2016-08-23
replythread ARM with scalable vector extensions new - Jorcy Neto - 2016-08-23
last reply ARM with scalable vector extensions new - Hubert Lamontagne - 2016-08-26
last reply ARM with scalable vector extensions new - Jorcy Neto - 2016-12-20
replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-09-05
replythread Proposal for instruction set - now on Github new - Agner - 2016-09-05
replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-09-05
last replythread Proposal for instruction set - now on Github new - Agner - 2016-09-06
reply Proposal for instruction set - now on Github new - Bigos - 2016-09-06
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-09-06
last replythread Proposal for instruction set - now on Github new - Agner - 2016-09-07
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-09-07
last replythread Proposal for instruction set - now on Github new - Agner - 2016-09-08
last reply Proposal for instruction set - now on Github new - Hubert Lamontagne - 2016-09-08
last replythread Proposal for instruction set - now on Github new - Commenter - 2016-09-07
last reply Proposal for instruction set - now on Github new - Bigos - 2016-09-08
last replythread Paging new - Kurt Baumgardner - 2016-09-09
replythread Paging new - Agner - 2016-09-10
reply Paging new - Hubert Lamontagne - 2016-09-11
last replythread Paging new - Kurt Baumgardner - 2016-09-13
replythread Paging new - Agner - 2016-09-13
last reply Paging new - Kurt Baumgardner - 2016-09-13
last replythread Paging new - Hubert Lamontagne - 2016-09-13
last reply Paging new - Kurt Baumgardner - 2016-09-14
replythread Paging new - Hubert Lamontagne - 2016-09-11
last reply Paging new - Kurt Baumgardner - 2016-09-13
last replythread Paging new - Agner - 2016-09-14
last reply Paging new - Jorcy Neto - 2016-09-18
replythread A null register? new - csdt - 2016-09-23
last replythread A null register? new - Agner - 2016-09-24
last replythread A null register? new - Hubert Lamontagne - 2016-09-24
replythread A null register? new - csdt - 2016-09-26
last reply A null register? new - Agner - 2016-09-27
last replythread Indexed registers new - Kurt Baumgardner - 2016-09-26
last replythread Indexed registers new - Agner - 2016-09-27
replythread Indexed registers new - Kurt Baumgardner - 2016-09-27
last reply Indexed registers new - Agner - 2016-09-28
last replythread Indexed registers new - Hubert Lamontagne - 2016-09-28
last replythread Indexed registers new - Kurt Baumgardner - 2016-10-03
reply Indexed registers new - Agner - 2016-10-03
last replythread Indexed registers new - Hubert Lamontagne - 2016-10-04
last replythread Bilinear Interpolation new - Hubert Lamontagne - 2016-10-28
last replythread Bilinear Interpolation new - Agner - 2016-10-29
last replythread Bilinear Interpolation new - Hubert Lamontagne - 2016-10-29
last replythread Bilinear Interpolation new - Agner - 2016-10-30
last reply Bilinear Interpolation new - Hubert Lamontagne - 2016-10-30
replythread ForwardCom version 1.04 new - Agner - 2016-12-08
replythread ForwardCom version 1.04 new - Matthias Bentrup - 2016-12-12
last replythread ForwardCom version 1.04 new - Agner - 2016-12-12
last reply ForwardCom version 1.04 new - Matthias Bentrup - 2016-12-14
last replythread Async system calls; horizontal packing instruction new - Joe Duarte - 2016-12-14
reply Async system calls; horizontal packing instruction new - Agner - 2016-12-15
last replythread Comparison of instruction sets new - Agner - 2016-12-17
replythread Comparison of instruction sets new - Joe Duarte - 2016-12-28
reply Comparison of instruction sets new - Agner - 2016-12-29
last reply Comparison of instruction sets new - Hubert Lamontagne - 2016-12-30
last reply Comparison of instruction sets new - Hubert Lamontagne - 2017-01-05
replythread ForwardCom version 1.05 new - Agner - 2017-01-22
replythread Syscall/ISR acceleration new - Jonathan Brandmeyer - 2017-01-22
last replythread Syscall/ISR acceleration new - Agner - 2017-01-23
last replythread Syscall/ISR acceleration new - Jonathan Brandmeyer - 2017-01-25
last reply Syscall/ISR acceleration new - Agner - 2017-01-25
replythread ForwardCom version 1.05 new - Jiří Moravec - 2017-01-23
last reply ForwardCom version 1.05 new - Agner - 2017-01-24
last replythread Jump prefetch? new - csdt - 2017-01-27
last replythread Jump prefetch? new - Agner - 2017-01-27
last replythread Jump prefetch? new - csdt - 2017-01-30
last replythread Jump prefetch? new - Agner - 2017-01-30
last replythread Jump prefetch? new - csdt - 2017-01-30
replythread Jump prefetch? new - Agner - 2017-01-31
reply Jump prefetch? new - csdt - 2017-01-31
last replythread Jump prefetch? new - Hubert Lamontagne - 2017-02-01
last replythread Jump prefetch? new - Agner - 2017-02-01
last replythread Jump prefetch? new - Hubert Lamontagne - 2017-02-01
last replythread Jump prefetch? new - Agner - 2017-02-02
last reply Jump prefetch? new - Agner - 2017-02-14
last replythread Jump prefetch? new - Hubert Lamontagne - 2017-01-31
last replythread High precision arithmetic new - fanoI - 2017-03-21
last reply High precision arithmetic new - Agner - 2017-03-21
replythread Intel's Control-flow Enforcement Technology new - Joe Duarte - 2017-04-13
last reply Intel's Control-flow Enforcement Technology new - Agner - 2017-04-14
reply Proposal for instruction set - now on Github new - Agner - 2017-04-27
replythread Assembler with metaprogramming features new - Agner - 2017-07-27
last replythread Assembler with metaprogramming features new - Kai Rese - 2017-08-11
last replythread Assembler with metaprogramming features new - Agner - 2017-08-11
last replythread Assembler with metaprogramming features new - Kai Rese - 2017-08-14
last replythread Assembler with metaprogramming features new - Agner - 2017-08-14
last reply Assembler with metaprogramming features new - Kai Rese - 2017-08-15
replythread Number of register file ports in implementations new - Hubert Lamontagne - 2017-08-22
last replythread Number of register file ports in implementations new - Agner - 2017-08-23
last replythread Number of register file ports in implementations new - Hubert Lamontagne - 2017-08-27
last replythread Number of register file ports in implementations new - Agner - 2017-08-28
reply Number of register file ports in implementations new - Bigos - 2017-08-28
last reply Number of register file ports in implementations new - Hubert Lamontagne - 2017-08-28
last replythread Proposal for instruction set - now on Github new - yeengief - 2017-09-20
replythread Proposal for instruction set - now on Github new - Agner - 2017-09-20
last replythread Proposal for instruction set - now on Github new - yeengief - 2017-09-20
last replythread Proposal for instruction set - now on Github new - Agner - 2017-09-20
last replythread Proposal for instruction set - now on Github new - yeengief - 2017-09-21
last replythread Proposal for instruction set - now on Github new - Agner - 2017-09-21
last replythread Proposal for instruction set - now on Github new - yeengief - 2017-09-21
last reply Proposal for instruction set - now on Github new - Agner - 2017-09-23
replythread Proposal for instruction set - now on Github new - - - 2017-09-22
last reply Proposal for instruction set - now on Github new - Agner - 2017-09-23
last replythread Proposal for instruction set - now on Github new - Hubert Lamontagne - 2017-09-25
last replythread Proposal for instruction set - now on Github new - Agner - 2017-09-26
last reply Proposal for instruction set - now on Github new - Hubert Lamontagne - 2017-09-26