Wed, 23 Jun 2010 21:17:44 -0700 (PDT)

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Type demotion of induction variable for address calculation shreyas76@gmail.com (shrey) (2010-06-23) |

From: | shrey <shreyas76@gmail.com> |

Newsgroups: | comp.compilers |

Date: | Wed, 23 Jun 2010 21:17:44 -0700 (PDT) |

Organization: | Compilers Central |

Keywords: | analysis, optimize, question |

Posted-Date: | 25 Jun 2010 16:25:39 EDT |

Hi all

I wish to explore the scenarios when the type of an induction

variable used say to index A[i[ in a loop can be demoted to a short.

The motivation being it would aid in an efficient code using 16 bit

multiplies instead of needing 32 bit multiplies for the target.

So far I can see the following cases

1. Size of A is less than 2^32 and assuming the source does not do out

of array access. Does c99 provide such guarrantees ?

2. the maximum value of i is less that 2^16/ sizeof(A[i])

Size of A[i] is size of element.

Is my reasoning valid ? And are there other scenarios ?

Also can some one point to me any such existing work ?

thanks

shrey

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