LabVIEW Compiler Optimizations

[SercoSteveB]

What do the hash marks on wires shown in the VI below indicate?

a) LabVIEW has created a reference to this section of code

b) LabVIEW has constant folded this section of code.

c) LabVIEW has identified this section of code for buffer reuse

d) LabVIEW has performed compile-time inlining on this section of code

[crossrulz]

B

Just so people know, there's a setting in the options menu to turn that on or off.

[Kumarhatti]

hey crossrulz

                    can you give brief explaination for this question.

[crossrulz]

Constant folding is an optimization method.  In simple terms, when compiling LabVIEW is turning that whole code into a constant and indicator (a constant 15 wired into the x+y indicator in this case).  It makes things run faster.  The hash marks on the wires shows where LabVIEW is performing this optimization.  You need to be careful about these.  I've had constant folding into an array and the file becomes to large.

[MrStevenUND]

I haven't seen this before.  What version of LabVIEW was this first released in?

[crossrulz]

At least as far as 8.2.1 (that's the oldest version I have here).

[MrStevenUND]

Interesting.    I'm using 8.2, 8.6.1, and 2009 SP1.  I've never seen it. (granted, this is poor coding and should be avoided)

[crossrulz]

The showing of the constant folding is OFF by default.  If you go into the Options dialog and then to the Block Diagram tab, you will find the Show Constant Folding for wires and another one for structures.

[SercoSteveB]

I see it all the time, my BDs are just one big blur

I can't get the structure constant folding to work (LV 2009).  Any thoughts?

[taper]

Should add that LabVIEW performs the constant folding whether or not you show it.  The option is strictly UI.

[mini09]

Learned a new stuff but need more on documents on this question. Nice explanation Crossrulz.

[SercoSteveB]

Answer: B.  Nice one crossrulz

I recommend checking out LabVIEW compiler optimizations and what is happening in the DFIR and LLVM, awesome page on ni.com. here.

[adiveppa]

Ans is B