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coder.loop.interchange

Interchange loop indices in generated code

Since R2023a

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    Syntax

    coder.loop.interchange("loopA_ID","loopB_ID")
    loopObj = coder.loop.interchange(___)

    Description

    coder.loop.interchange("loopA_ID","loopB_ID") prompts the code generator to interchange the for loops with index names loopA_ID and loopB_ID in the generated code.

    Use this transform when accessing array elements stored in contiguous memory blocks. In such situations, the data is loaded into cache and can be reused without a cache refresh.

    For more information about loop optimizations, see Optimize Loops in Generated Code.

    example

    loopObj = coder.loop.interchange(___) creates a loop control object with transformSchedule property set to coder.loop.interchange. Use the apply method to apply the transform to the specified loop.

    Examples

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    Open Live Script

    You can use the coder.loop.interchange function to swap for-loops in the generated code. This optimization can improve cache performance when accessing array elements in your code.

    Define a MATLAB® function interchangeForLoops that operates on a matrix by using two for-loops. Call the coder.loop.interchange function immediately before the for-loop to optimize.

    type interchangeForLoops.m
    function out = interchangeForLoops()
out = zeros(100,70);

coder.loop.interchange('i','j');
for i = 1:100
    for j = 1:70
        out(i,j) = out(i,j) + i*j;
    end
end

    Generate code for this function at the command line.

    codegen interchangeForLoops -config:lib
    Warning: Code generation is using a coder.EmbeddedCodeConfig object. Because
Embedded Coder is not installed, this might cause some Embedded Coder features
to fail.

Code generation successful (with warnings): To view the report, open('codegen/lib/interchangeForLoops/html/report.mldatx')

    Inspect the generated code. The indices for-loops are swapped in the generated code. The data elements are loaded into cache in a contiguous block and a larger portion of the cache is reused within the inner loop.

    type(fullfile("codegen","lib","interchangeForLoops","interchangeForLoops.c"))
    /*
 * File: interchangeForLoops.c
 *
 * MATLAB Coder version            : 24.2
 * C/C++ source code generated on  : 05-Sep-2024 16:34:18
 */

/* Include Files */
#include "interchangeForLoops.h"
#include <string.h>

/* Function Definitions */
/*
 * Arguments    : double out[7000]
 * Return Type  : void
 */
void interchangeForLoops(double out[7000])
{
  int i;
  int j;
  memset(&out[0], 0, 7000U * sizeof(double));
  for (j = 0; j < 70; j++) {
    for (i = 0; i < 100; i++) {
      int out_tmp;
      out_tmp = i + 100 * j;
      out[out_tmp] += (double)((i + 1) * (j + 1));
    }
  }
}

/*
 * File trailer for interchangeForLoops.c
 *
 * [EOF]
 */

    Input Arguments

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    for loop identifier or index name to interchange, specified as a character vector a string scalar.

    Data Types: char | string

    for loop identifier or index name to interchange, specified as a character vector a string scalar.

    Data Types: char | string

    Output Arguments

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    Loop control object with transformSchedule property set to coder.loop.interchange.

    Version History

    Introduced in R2023a

    See Also

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