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Assertions also let you choose subroutines that you think are good candidates for inlining. However, subject to its thresholds, the compiler may reject your choices. Inlining could expand the code so much that increased memory activity would claim back gains made by eliminating the procedure call. At higher optimization levels, the compiler is often capable of making its own choices for inlining candidates, provided it can find the source code for the routine under consideration.

Some compilers support a feature called interprocedural analysis . When this is done, the compiler looks across routine boundaries for its data flow analysis. It can perform significant optimizations across routine boundaries, including automatic inlining, constant propagation, and others.

No side effects

Without interprocedural analysis, when looking at a loop, if there is a subroutine call in the middle of the loop, the compiler has to treat the subroutine as if it will have the worst possible side effects. Also, it has to assume that there are dependencies that prevent the routine from executing simultaneously in two different threads.

Many routines (especially functions) don’t have any side effects and can execute quite nicely in separate threads because each thread has its own private call stack and local variables. If the routine is meaty, there will be a great deal of benefit in executing it in parallel.

Your computer may allow you to add a directive that tells you if successive sub-routine calls are independent:


C$ASSERT NO_SIDE_EFFECTS DO I=1,NCALL BIGSTUFF (A,B,C,I,J,K) END DO

Even if the compiler has all the source code, use of common variables or equivalences may mask call independence.

Manual parallelism

At some point, you get tired of giving the compiler advice and hoping that it will reach the conclusion to parallelize your loop. At that point you move into the realm of manual parallelism. Luckily the programming model provided in FORTRAN insulates you from much of the details of exactly how multiple threads are managed at runtime. You generally control explicit parallelism by adding specially formatted comment lines to your source code. There are a wide variety of formats of these directives. In this section, we use the syntax that is part of the OpenMP (see [link] ) standard. You generally find similar capabilities in each of the vendor compilers. The precise syntax varies slightly from vendor to vendor. (That alone is a good reason to have a standard.)

The basic programming model is that you are executing a section of code with either a single thread or multiple threads. The programmer adds a directive to summon additional threads at various points in the code. The most basic construct is called the parallel region .

Parallel regions

In a parallel region, the threads simply appear between two statements of straight-line code. A very trivial example might be the following using the OpenMP directive syntax:


PROGRAM ONE EXTERNAL OMP_GET_THREAD_NUM, OMP_GET_MAX_THREADSINTEGER OMP_GET_THREAD_NUM, OMP_GET_MAX_THREADS IGLOB = OMP_GET_MAX_THREADS()PRINT *,’Hello There’ C$OMP PARALLEL PRIVATE(IAM), SHARED(IGLOB)IAM = OMP_GET_THREAD_NUM() PRINT *, ’I am ’, IAM, ’ of ’, IGLOBC$OMP END PARALLEL PRINT *,’All Done’END

Questions & Answers

what is math number
Tric Reply
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
I'm 13 and I understand it great
AJ
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Atone
hi
Adu
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
Vedant
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
Augustine
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
AJ
how
Sheref
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
hi
salma
hi
Ayuba
Hello
opoku
hi
Ali
greetings from Iran
Ali
salut. from Algeria
Bach
hi
Nharnhar
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
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