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Quick Q: Is final used for optimization in C++?

By Adrien Hamelin | May 27, 2016 02:37 PM | Tags: performance intermediate

Quick A: Possibly.

Recently on SO:

Is final used for optimization in C++?

It can be.

An optimisation along these lines would relate to the "de-virtualization" of the virtual calls. This is not always immediately affected by the final of the class nor method. Albeit they offer help to determine this, the normal rules of the virtual functions and class hierarchy apply.

If the compiler can determine that at runtime a particular method will always be called (e.g. given the OP example, with an automatic object), it could apply such an optimisation anyway, irrespective of whether the method is final or not.

Optimisations fall under the as-if rule, that allow the compiler to apply any transformation so long as the observable behaviour is as-if the original code had been executed.

CppCon 2015 C++ Multi-dimensional Arrays...--Pramod Gupta

By Adrien Hamelin | May 25, 2016 01:43 PM | Tags: performance intermediate

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

C++ Multi-dimensional Arrays...

by Pramod Gupta

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

The language feature of passing a multi-dimensional array to a function without specifying all its dimensions at compile time is crucial for computational physics and applied mathematics. For example a matrix is a two dimensional array and a matrix inversion function which needs to know the size of the matrix at compile time would be of limited use. Major general purpose languages such as C, Java and C# support this feature. Of course, scientific programming languages like Fortran, Matlab and R also support this feature.

C++ is perhaps the only major programming language which does not allow passing a multi-dimensional array to a function unless the size of all the dimensions except the first one is known at compile time. Due to this limitation of C++, various libraries have been developed for using multi-dimensional arrays in C++. Some of these libraries are Blitz++, Armadillo, Eigen and boost.multi_array. These libraries are very large and complex. While they do provide a wide variety of features, they have a learning curve which may be difficult to justify for something as basic as passing multi-dimensional arrays to functions. Also the computational physics or applied mathematics code becomes dependent on a large non-standard library. Hence its usage will be limited to only those scientists who are willing to install these non-standard libraries.

The reference feature of C++ allows us to develop a multi-dimensional array class. The class has a small number of lines of code and hence the code can be included with the scientific application code. We use this class to write programs for various areas of computational physics and show that the class is easy to use and it leads to readable programs.

CppCon 2015 Faster Complex Numbers--André Bergner

By Adrien Hamelin | May 20, 2016 02:39 PM | Tags: performance c++11

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Faster Complex Numbers

by André Bergner

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Complex numbers are an important tool from mathematics enabling many problems to be written in a more generic form. The C++ standard library comes with an implementation to work with complex numbers in a natural way.

Motivated by useful real world examples from theoretical physics and audio dsp I will discuss benchmarks of std::complex and demonstrate how alternative implementations, naïve or advanced ones based on expression templates, outperform std::complex and can compete with hand-crafted C code (depending on compiler and std lib). A quick introduction to expression templates will be provided.

CppCon 2015 Memory and C++ debugging at Electronic Arts--Scott Wardle

By Adrien Hamelin | May 18, 2016 08:00 AM | Tags: performance efficiency

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Memory and C++ debugging at Electronic Arts

by Scott Wardle

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Scott Wardle a senior software engineer Electronic Arts will talk about the current memory and C++ debugging setup and tools used in games.

PS4 and Xbox One have virtual memory and 64 bit address spaces, GPU and CPU are getting closer in the ability to work virtual memory. So our tools are getting better and better and closer to PCs. Most of a games memory goes towards art and level data like bitmap textures and polygon meshes. So artist and designer need to understand how much their data takes up. Giving them call stacks of memory allocations does not help. They want to know how big is a group of building is. Why is this group of building bigger than this one? Maybe this one has some animation data or one of the textures is too big. But there are 10,000s of objects built by 100s of people all around the world.

CppCon 2015 Implementation of a component-based entity system in modern C++--Vittorio Romeo

By Adrien Hamelin | May 13, 2016 02:17 PM | Tags: performance efficiency c++14

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Implementation of a component-based entity system in modern C++

by Vittorio Romeo

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

An alternative to deep inheritance trees for game and application architecture design is "composition". Separating data (in independent components) from logic (in independent systems) allows the code to be more reusable and more efficient, alongside additional benefits. Using modern C++11 and C++14 features, it is possible to design an efficient and user-friendly component-based entity system library, with intuitive syntax and convenient cost-free abstractions.

CppCon 2015 Tuning C++: Benchmarks, and CPUs, and Compilers! Oh My!--Chandler Carruth

By Adrien Hamelin | May 9, 2016 01:24 PM | Tags: performance advanced

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Tuning C++: Benchmarks, and CPUs, and Compilers! Oh My!

by Chandler Carruth

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

A primary use case for C++ is low latency, low overhead, high performance code. But C++ does not give you these things for free, it gives you the tools to control these things and achieve them where needed. How do you realize this potential of the language? How do you tune your C++ code and achieve the necessary performance metrics?

This talk will walk through the process of tuning C++ code from benchmarking to performance analysis. It will focus on small scale performance problems ranging from loop kernels to data structures and algorithms. It will show you how to write benchmarks that effectively measure different aspects of performance even in the face of advanced compiler optimizations and bedeviling modern CPUs. It will also show how to analyze the performance of your benchmark, understand its behavior as well as the CPUs behavior, and use a wide array of tools available to isolate and pinpoint performance problems. The tools and some processor details will be Linux and x86 specific, but the techniques and concepts should be broadly applicable.

Introducing a new, advanced Visual C++ code optimizer--Gratian Lup

By Adrien Hamelin | May 5, 2016 11:35 PM | Tags: performance efficiency

Visual C++ compiler evolves again:

Introducing a new, advanced Visual C++ code optimizer

by Gratian Lup

From the article:

We are excited to announce the preview release of a new, advanced code optimizer for the Visual C++ compiler backend. It provides many improvements for both code size and performance, bringing the optimizer to a new standard of quality expected from a modern native compiler.

This is the first public release and we are encouraging people to try it and provide suggestions and feedback about potential bugs. The official release of the new optimizer is expected to be Visual Studio Update 3, while the release available today is unsupported and mostly for testing purposes...

Fast incremental sort -- Lars Hagen

By larshagencpp | Apr 24, 2016 05:34 AM | Tags: performance efficiency

Lars Hagen describes in his blog post a strategy to solve the problem of a fast incremental sort.

Fast incremental sort

by Lars Hagen

From the article

I recently came across the need for an incremental sorting algorithm, and started to wonder how to do it optimally.

The incremental sorting problem is described here, and is an “online” version of partial sort. That is, if you have already sorted kk elements, you should be able to quickly sort k+1k+1 elements, and so on.

Incremental sorts can be useful for a number of cases:

  • You want sorted items, but you don’t know how many elements you’ll need. This could often happen when you are filtering the resulting sequence, and you don’t know how many items will be filtered out.
  • You are streaming the sequence, so even though you want the whole sequence, you want the first elements as quickly as possible.

We’ll see how branch misprediction and other constant factors can make the naive asymptotically optimal version far slower than a practical implementation.