New optimizations for X86 in upcoming GCC 5.0 -- Evgeny Stupachenko

Fresh on the Intel Developer Zone blog:

New optimizations for X86 in upcoming GCC 5.0

by Evgeny Stupachenko

From the article:

Part 1. Vectorization of loads/stores group.

GCC 5.0 significantly improves vector code quality for load groups and store groups. By loads/stores group I mean iterated consecutive sequence of loads/stores. For example:

x = a[i], y = a[i + 1], z = a[i + 2] iterated by “i” is loads group of size 3


The most frequent case where loads/stores groups are applicable is array of structures.
  1. Image conversion (RGB structure to some other) ...
  2. N-dimentional coordinates. (Normalize array of XYZ points) ...
  3. Multiplication of vectors by constant matrix: ...

... GCC 5.0:

  1. Introduces vectorization of load/store groups of size 3
  2. Improves load groups vectorization for all supported sizes
  3. Maximizes load/store groups performance by generating code that is more optimal for particular x86 CPU...


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