Different General Purpose Registers take more cycles ?

Question

0.00/5 (No votes)

See more:

I have a loop in my Intel Vector assembly code. In the loop, the loop counter is used to read from and write to 4 consecutive memory locations. For example,

vmovdqu [r9 + rdx + 64], y0<br />
 vmovdqu [r9 + rdx + 96], y1

where is my loop counter. During profiling, I notice that using "r10d" instead of "rdx" register increases cycles. The initialisation to "r10d" takes 1 byte more than that to "rdx". What could be the reason for the cycle increase ?

Posted 3-Mar-14 4:30am

Member 9964804

Add a Solution

Comments

Krunal Rohit 3-Mar-14 10:35am

rdx is your loop counter ?

-KR

Member 9964804 3-Mar-14 10:55am

Yes ... Type .. sorry !

Sergey Alexandrovich Kryukov 3-Mar-14 10:44am

This is the internal business of the CPU. Its documentation contains all cycle counts for all cases.
—SA

Member 9964804 3-Mar-14 10:57am

Nope .. it doesn't differentiate between GPRs.

Sergey Alexandrovich Kryukov 3-Mar-14 11:01am

Hm...
—SA

2 solutions

Solution 2

Hi KR , I have the instruction manual, but it does not give me any pointers.
The closest I came to a solution is here: http://stackoverflow.com/questions/17896714/why-would-introducing-useless-mov-instructions-speed-up-a-tight-loop-in-x86-64-a[^]

Posted 3-Mar-14 4:56am

Member 9964804

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Krunal Rohit · Accepted Answer · 2014-03-03T04:50:00

Solution 1

Well, You may find that info in the documentation called Instruction Manual provided by manufacturer of the processor. Every processor manufacturer provides this documentation, but yeah it is not free. You have to pay for that. :)

-KR

Posted 3-Mar-14 4:50am

Krunal Rohit

v2