@verbatim
Data references and dependences detectors. Copyright (C) 2003-2013 Free Software Foundation, Inc. Contributed by Sebastian Pop pop@c.nosp@m.ri.e.nosp@m.nsmp..nosp@m.fr
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see http://www.gnu.org/licenses/.
This pass walks a given loop structure searching for array
references. The information about the array accesses is recorded
in DATA_REFERENCE structures.
The basic test for determining the dependences is:
given two access functions chrec1 and chrec2 to a same array, and
x and y two vectors from the iteration domain, the same element of
the array is accessed twice at iterations x and y if and only if:
| chrec1 (x) == chrec2 (y).
The goals of this analysis are:
- to determine the independence: the relation between two
independent accesses is qualified with the chrec_known (this
information allows a loop parallelization),
- when two data references access the same data, to qualify the
dependence relation with classic dependence representations:
- distance vectors
- direction vectors
- loop carried level dependence
- polyhedron dependence
or with the chains of recurrences based representation,
- to define a knowledge base for storing the data dependence
information,
- to define an interface to access this data.
Definitions:
- subscript: given two array accesses a subscript is the tuple
composed of the access functions for a given dimension. Example:
Given A[f1][f2][f3] and B[g1][g2][g3], there are three subscripts:
(f1, g1), (f2, g2), (f3, g3).
- Diophantine equation: an equation whose coefficients and
solutions are integer constants, for example the equation
| 3*x + 2*y = 1
has an integer solution x = 1 and y = -1.
References:
- "Advanced Compilation for High Performance Computing" by Randy
Allen and Ken Kennedy.
http://citeseer.ist.psu.edu/goff91practical.html
- "Loop Transformations for Restructuring Compilers - The Foundations"
by Utpal Banerjee.