What are the things vbc.exe does when /optimize switch is used?

Question

vbc.exe has something called /optimize switch right. If I enable that what are the optimizations the compiler can do for me? The MSDN documentation just curtly says 'does various compiler optimizations'. Where can I find the complete quantified view of the different optimizations that actually goes into.

Here is the thing I am pursuing this route. One of the code blocks in a module I am leading has a lot of delimited array manipulations. I believe this is going to be a heck costly in terms of string memory handling. I am looking to see if I can retire them by way of simple properties or methods so that the compiler can internally do something like our c++ inline functions making a best win-win offer in terms of both memory and processing time. I admit when the compiler translates them as inline function, the JITed code might be big in size right?

Answer 1

Some general optimizations are...... Well, I don't elaborate on this because it's not specific to the JIT-compiler:

http://en.wikipedia.org/wiki/Compiler_optimization

For example, I made a performance test that contained the line
   i += j
   i += j
   i += j
   i += j
   ....

100 times. The compiler changed it to i += j * 100

A little story:

I once wrote simple Bitmap processing code in VB.Net. It wasn't made for speed, so I've used GetPixel/SetPixel, which is the slowest version you can write. I've optimized the code by using Bitmap.LockBits/UnlockBits. The next version was written in C# with unsafe code blocks. Another version was written in unmanaged C++, and one more I wrote in pure assembler code. Surprisingly the optimized C# version was the quickest one, even faster than the optimized C++ version.

---

Armin

Answer 2

@Armin,

That was really a brief but wonderful description about the proposed optimizations. Do these apply to vbc.exe as well?

Answer 3

@Armin,

That was really a brief but wonderful description about the proposed optimizations. Do these apply to vbc.exe as well?

I don't know. Personally I don't care because I can't change it anyway. For debugging, they are disabled, otherwise enabled.

Anyway they are done by the JIT-compiler, not by Vbc.exe.

Here are some articles about it (but I can also only google like you can): 

http://blogs.msdn.com/b/davidnotario/archive/2004/10/28/248953.aspx

http://blogs.msdn.com/b/davidnotario/archive/2004/11/01/250398.aspx

http://www.codeproject.com/Articles/25801/JIT-Optimizations

---

Armin

Answer 4

Hi Deepak,

Welcome to the MSDN Forum.

Add to the others, please take a look at this blog: http://blogs.msdn.com/b/ericlippert/archive/2009/06/11/what-does-the-optimize-switch-do.aspx 

Best regards,

---

Mike Feng
MSDN Community Support | Feedback to us
Please remember to mark the replies as answers if they help and unmark them if they provide no help.

Answer 5

Hi Deepak,

We don't hear from you a couple of days.

Do you have any update?

How about your issue now?

Best regards,

---

Mike Feng
MSDN Community Support | Feedback to us
Please remember to mark the replies as answers if they help and unmark them if they provide no help.

Answer 6

Dear Mike,

Both Wiki and other MSDN blog URLs were informative.

Thanks and Regards,

Deepak

Answer 7

I didn't see in those interesting articles linked to in the other replies any direct mention of optimising Select Case statements, but the compiler can also use branch tables.

--
Andrew