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[[Category:SPO600 Labs- Retired]]{{Chris Tyler Draft}}
{{Admon/lab|Purpose of this Lab|This lab is designed to explore single instruction/multiple data (SIMD) vectorization, and the auto-vectorization capabilities of the GCC compiler.}}
{{Admon/tip|Tiny Lab|This is intended to be a very short lab. Don't overcomplicate it!}}
{{Admon/important|This lab is not used in the current semester.|Please refer to the other labs in the [[:Category:SPO600 Labs|SPO600 Labs]] category.}}
== Optional Lab (Recommended!) == # Write the shortest C a short program that can be vectorized creates two 1000-element integer arrays and fills them with random numbers in the range -1000 to +1000, then sums those two arrays element-by GCC-element to a third array, and finally sums the third array and prints the result.# Compile this program on one of the AArch64/ARM64 [[SPO600 Servers#AArch64|aarchie]]in such a way that the code is auto-vectorized.
# Annotate the emitted code (i.e., obtain a dissassembly via <code>objdump -d</code> and add comments to the instructions in <code><main></code> explaining what the code does).
# '''Write a blog post discussing your findings'''. Include:
#* The source code
#* The compiler command line used to build the code
#* Your annotated dissassembly listing- '''Prove that the code is vectorized''', for example, by pointing out the use of vector registers and SIMD instructions.
#* Your reflections on the experience and the results
=== Resources ===
* [https://gcc.gnu.org/projects/tree-ssa/vectorization.html Auto-Vectorization in GCC] - Main project page for the GCC auto-vectorizer.
* [http://locklessinc.com/articles/vectorize/ Auto-vectorization with gcc 4.7] - An excellent discussion of the capabilities and limitations of the GCC auto-vectorizer, intrinsics for providing hints to GCC, and other code pattern changes that can improve results. Note that there has been some improvement in the auto-vectorizer since this article was written. '''This article is strongly recommended.'''
* [https://software.intel.com/sites/default/files/8c/a9/CompilerAutovectorizationGuide.pdf Intel (Auto)Vectorization Tutorial] - this deals with the Intel compiler (ICC) but the general technical discussion is valid for other compilers such as gcc and llvm