execution frequency of header of a loop - optimization

In a LLVM pass, I'd like to record the loop trip count of a loop. One part I did was inserting a function call before the terminator of the header block of each loop. I found that this method did not work well, because if a loop has n iterations, the header block will be executed n+1 times. This fact holds for "for" and "while" loop, but it does not hold for "do while" loop. I insert the function call to the second block of "for" and "while" loops, and to the first block of "do while" loops. This works only if I know a priori the kind the targeted loop, which is impossible through purely bitcode. My question is: is there a universal way (handling all kinds of loops) to insert a function call, which will be called exactly the same times as the number of iterations.


Put the function call at the start of the body of the loop. Why are you trying to put it in the header?
for (...) {
increment_trip_count();
...
}


If you insert the function call in the beginning of the loop body, you will get the correct count.

Related

Is the `return` statement necessary at the end of an AHK script?

My one-line script:
Shift::Send ^{Space}
Is it necessary to add a return statement like the following?
Shift::Send ^{Space}
return

In the case of a subroutine with a label like you show above, the subroutine will be called and will continue until it gets to either return or exit.
So in this example, return isn't necessary
With functions, return is actually assumed in ahk so you don't necessarily need to include it unless your passing it with an expression.
In either case though, you might want to include it just to make things more readable.

Quote an example from the return documentation to demonstrate what it does:
The first Return separates the hotkey from the subroutine below. If it were not present, pressing the hotkey would cause Sleep 1000 to be executed twice.
#z::
MsgBox The Win-Z hotkey was pressed.
Gosub MySubroutine
return
MySubroutine:
Sleep 1000
return
Also, quote from Hotkeys Introduction and Simple Examples:
If a hotkey needs to execute only a single line, that line can be listed to the right of the double-colon. In other words, the return is implicit:
#n::Run Notepad
As a side note, if binding multiple hotkeys to the same action, we can write:
#a::
#b::MsgBox

Kotlin error "Index Out Of Bounds Exception"

I'm newbie to Kotlin, and new to programming also, so pls be gentle :)
Let's say I have a string (it was optimized to NOT have any duplicated character), i want to compare all characters in that string to the alphabet, which declared as a mutable List of character. I want to delete any character from the alphabet which show up in the string. My code is as below
var alphabet=mutableListOf('a','b','c','d','e','f','g','h','i','j','k','l','m',
'n','o','p','q','r','s','t','u','v','w','x','y','z')
var key="keyword"
println(key)
for (i in key.indices)
{for (j in alphabet.indices)
{if (key[i] == alphabet[j])
alphabet.removeAt(j) // 1. this line have error
//print(alphabet[j]) //2. but this line runs fine
}}}
In above code, I have error at the "alphabet.removeAt(j)" command, so I try another command to print out the characters instead of delete them, and it runs fine. I read some articles and I know this error related to the invalid index, but I used the "indices" key and I think it's pretty safe. Pls help

It is safe to iterate using alphabet.indices, but it is not safe to iterate over a collection while modifying it. Note that indices returned indices for a full alphabet, but then you removed some items from it, making it shorter, so indices are no longer valid.
You don't need to iterate over a collection to find an item to remove. You can just do:
alphabet.remove(key[i])
But honestly, you don't need to do anything of this. Your problem is really a subtracting of two sets and you can solve it much easier:
('a'..'z').toSet() - "keyword".toSet()

You could simplify that whole loop to just:
alphabet.retainAll{ it !in key })
or
alphabet.retainAll { !key.contains(it) }
or if you want the filtered list to be a new list rather than doing it in-place:
val filtered = alphabet.filter { it !in key }

but I used the "indices" key and I think it's pretty safe
Well, the indices collection is only evaluated once when a loop is entered, not at the start of each iteration. Even if you change the size of alphabet in the inner loop, the inner loop will still loop the same number of times, because it doesn't evaluate alphabet.indices again. It would only do that again on the next iteration of the outer loop, but your code would throw an exception before that point.
Other than decreasing j whenever you remove an item, you can also solve this by
key.forEach(alphabet::remove)

Why does nested LOOP AT SCREEN cause infinite loop/recursion?

Here is one for you. Although such a language construction does not make much sense I would like to know why the nested LOOP AT SCREEN cause infinite loop (recursion?).
Let us take the following simple program.
REPORT yyy.
PARAMETERS:
p_x1 TYPE abap_bool.
AT SELECTION-SCREEN OUTPUT.
LOOP AT SCREEN.
BREAK-POINT.
ENDLOOP.
The BREAK-POINT statement will be executed only 4 times. This leads to an assumption that such a nested loop would run 16 times. Instead the below mentioned program runs forever and ends with a timeout exception.
REPORT yyy.
PARAMETERS:
p_x1 TYPE abap_bool.
AT SELECTION-SCREEN OUTPUT.
LOOP AT SCREEN.
LOOP AT SCREEN.
ASSERT 1 = 1.
ENDLOOP.
ENDLOOP.
It looks like nesting LOOP AT SCREEN causes either an infinite loop or some kind of an infinite recursion.
Why is it so? Is it documented somewhere? The extended check does not report anything regarding the loop. The same applies to Code Inspector as well.
EDIT
I have also checked whether this is a general problem for internal tables with a header line. It seems not.
REPORT YYY.
DATA: gt_t000 TYPE t000 OCCURS 10 WITH HEADER LINE.
START-OF-SELECTION.
SELECT * FROM t000
INTO TABLE gt_t000[].
LOOP AT gt_t000.
LOOP AT gt_t000.
WRITE / gt_t000-mandt.
ENDLOOP.
ENDLOOP.

Getting KeyError when trying to create multiple variables in for loop ("post0", "post1", etc.)

Very new to python - just started actually using it yesterday. I'm running a for loop that scans a text file and copies specific parts of it into variables that will then be put into a class "post". I want to create a new post at the bottom of the loop, named "post0", "post1", and so on, corresponding with the number of times the for loop has been run. This is what I'm trying to use:
postname = globals()['post%s' % s]
And I currently am trying to have it print the name of the post every time it creates one with a simple print(postname). 's' is the variable the for loop runs off of, if that makes sense. It starts at 0 and runs up to the number of lines in the text file, currently 424.
When I run the code, it returns "KeyError: post0". What am I doing wrong?
Also, reading around here it seems that creating variables this way is bad practice. If there is a more efficient way to do it I'd be happy to try that instead, but I'd also like to know how to make this method work just so I understand the concept. Thanks.
Edit: Problem solved! See my answer below.

I created a list postlist = [] outside of the loop, then inside the loop I append the list with a "post_" where "_" is the 's' variable. Looks like this:
postlist.append('post%s' % s)
Python is cool!

Is there a break statement in Mule <foreach>

I have an array list values which I loop using <foreach> and <choice>. As soon as the first hit happens in choice I want to come out of the foreach loop. Is there a way to break the loop?

foreach may look like a procedural construct but behind the scene it uses a standard message splitter so it actually produces a bunch of messages out of the original collection.
So there is no mean to break anything: filtering with a choice or filter is the way to go.