[LLVMdev] [RFC] [X86] Mov to push transformation in x86-32 call sequences

[Herbie Robinson]

But the r,m move has a reciprocal throughput of 0.5 while the pop is 1.

It sounds like this should be optional as you have already proposed.

On 12/22/14 2:21 AM, Kuperstein, Michael M wrote:
> The official Intel guide has less resolution here than we need.
> Consider that the MOV instruction described in C-21 only uses the ALU execution unit, not memory.
>
> If we look at Agner's table for Haswell, the relevant form of the MOV instruction (m,r) has a latency of 3 cycles and a reciprocal throughput of 1, same as a register PUSH.
> The same applies for other recent x86 processors.
>
> -----Original Message-----
> From: Caldarale, Charles R [mailto:Chuck.Caldarale at unisys.com]
> Sent: Monday, December 22, 2014 04:56
> To: Herbie Robinson; Kuperstein, Michael M; LLVMdev at cs.uiuc.edu
> Subject: RE: [LLVMdev] [RFC] [X86] Mov to push transformation in x86-32 call sequences
>
>> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
>> On Behalf Of Herbie Robinson
>> Subject: Re: [LLVMdev] [RFC] [X86] Mov to push transformation in x86-32 call sequences
>>> On 12/21/14 4:27 AM, Kuperstein, Michael M wrote:
>>> Which performance guidelines are you referring to?
>> Table C-21 in "Intel(r) 64 and IA-32 Architectures Optimization Reference Manual", September 2014.
>> It hasn't changed.  It still lists push and pop instructions as 2-3 times more expensive as mov.
> And verified by Agner Fog's independent measurements:
> http://www.agner.org/optimize/instruction_tables.pdf
>
> The relevant Haswell numbers are on pages 186 - 187.
>
>   -Chuck
>
> ---------------------------------------------------------------------
> Intel Israel (74) Limited
>
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>