loop interchanging

The loop interchanging transformation exchanges the indexes, the bounds and the steps of two nested do-loops statements ; the outer loop and an inner loop given by its internal level.

$\vartriangleright$ Example 64:  Interchange of the first and the third loops (indexes I and K). The level is 2.

    DO I=1,N
      DO J=2,M
        DO K=2,M
          CALL F(I,J,K)
        ENDDO
      ENDDO
    ENDDO

$\longrightarrow$

   DO K=2,M
     DO J=2,M
       DO I=1,N
         CALL F(I,J,K)
       ENDDO
     ENDDO
   ENDDO

  $\blacktriangleright$ Fits:LoopExchangeMulti:Check(OUTLOOP,DIAGMESG,LEVEL)

 
This function checks if the loop interchanging transformation can be applied to OUTLOOP.

• OUTLOOP (input AST) must be the outer do-loop statement
• DIAGMESG (output STRING) is the diagnostic string
• LEVEL (input INT) is the inner loop level (1 for the first inner loop).
• The function returns an error code (return INT):
  • 1 if all is correct
  • 0 if OUTLOOP is not a do-loop statement.
  • -1 if the inner loop is not found.
  • -2 if the bounds or the step of the inner loop depend of the index of OUTLOOP.
  • -3 if the inner loop contains statements that are not handled by the transformation.

  $\blacktriangleright$ Fits:LoopExchangeMulti:Advice(OUTLOOP,DIAGMESG,LEVEL)

 
This function emits a diagnostic about the interest of the loop interchanging transformation applied to OUTLOOP.

• OUTLOOP (input AST) must be the outer do-loop statement
• DIAGMESG (output STRING) is the diagnostic string
• LEVEL (input INT) is the inner loop level (1 for the first inner loop).
• The function returns a diagnostic code (return INT) :
  • 1 if the transformation is recommended
  • 0 if the transformation may be interesting
  • -1 if the transformation in not recommended

  $\blacktriangleright$ Fits:LoopExchangeMulti:Safe(OUTLOOP,DIAGMESG,LEVEL)

 
This function emits a diagnostic about the code produced by the loop interchanging transformation applied to OUTLOOP.

• OUTLOOP (input AST) must be the outer do-loop statement.
• DIAGMESG (output STRING) is the diagnostic string.
• LEVEL (input INT) is the inner loop level (1 for the first inner loop).
• The function returns a diagnostic code (return INT) :
  • 1 if the transformation is safe
  • 0 if the transformation may be safe. More information are given by the text in DIAGMESG.
  • -1 if the transformation is not safe

  $\blacktriangleright$ Fits:LoopExchangeMulti:Safe(DESC,VERBOSE,LEVEL)

 
This function applies the loop interchanging transformation to the loop OUTLOOP.

• DESC (input LOOPDESC) must be a the root node of a AST of loop descriptor with a depth greater of equal to LEVEL.
• VERBOSE (input INT) is the comment level
• The function returns the new do-loop statement created by the transformation (return AST).