+++ /dev/null
-/* Loop flattening for Graphite.
- Copyright (C) 2010 Free Software Foundation, Inc.
- Contributed by Sebastian Pop <sebastian.pop@amd.com>.
-
-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/>. */
-
-#include "config.h"
-#include "system.h"
-#include "coretypes.h"
-#include "tree-flow.h"
-#include "tree-dump.h"
-#include "cfgloop.h"
-#include "tree-chrec.h"
-#include "tree-data-ref.h"
-#include "tree-scalar-evolution.h"
-#include "sese.h"
-
-#ifdef HAVE_cloog
-#include "ppl_c.h"
-#include "graphite-ppl.h"
-#include "graphite-poly.h"
-
-/* The loop flattening pass transforms loop nests into a single loop,
- removing the loop nesting structure. The auto-vectorization can
- then apply on the full loop body, without needing the outer-loop
- vectorization.
-
- The loop flattening pass that has been described in a very Fortran
- specific way in the 1992 paper by Reinhard von Hanxleden and Ken
- Kennedy: "Relaxing SIMD Control Flow Constraints using Loop
- Transformations" available from
- http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.54.5033
-
- The canonical example is as follows: suppose that we have a loop
- nest with known iteration counts
-
- | for (i = 1; i <= 6; i++)
- | for (j = 1; j <= 6; j++)
- | S1(i,j);
-
- The loop flattening is performed by linearizing the iteration space
- using the function "f (x) = 6 * i + j". In this case, CLooG would
- produce this code:
-
- | for (c1=7;c1<=42;c1++) {
- | i = floord(c1-1,6);
- | S1(i,c1-6*i);
- | }
-
- There are several limitations for loop flattening that are linked
- to the expressivity of the polyhedral model. One has to take an
- upper bound approximation to deal with the parametric case of loop
- flattening. For example, in the loop nest:
-
- | for (i = 1; i <= N; i++)
- | for (j = 1; j <= M; j++)
- | S1(i,j);
-
- One would like to flatten this loop using a linearization function
- like this "f (x) = M * i + j". However CLooG's schedules are not
- expressive enough to deal with this case, and so the parameter M
- has to be replaced by an integer upper bound approximation. If we
- further know in the context of the scop that "M <= 6", then it is
- possible to linearize the loop with "f (x) = 6 * i + j". In this
- case, CLooG would produce this code:
-
- | for (c1=7;c1<=6*M+N;c1++) {
- | i = ceild(c1-N,6);
- | if (i <= floord(c1-1,6)) {
- | S1(i,c1-6*i);
- | }
- | }
-
- For an arbitrarily complex loop nest the algorithm proceeds in two
- steps. First, the LST is flattened by removing the loops structure
- and by inserting the statements in the order they appear in
- depth-first order. Then, the scattering of each statement is
- transformed accordingly.
-
- Supposing that the original program is represented by the following
- LST:
-
- | (loop_1
- | stmt_1
- | (loop_2 stmt_3
- | (loop_3 stmt_4)
- | (loop_4 stmt_5 stmt_6)
- | stmt_7
- | )
- | stmt_2
- | )
-
- Loop flattening traverses the LST in depth-first order, and
- flattens pairs of loops successively by projecting the inner loops
- in the iteration domain of the outer loops:
-
- lst_project_loop (loop_2, loop_3, stride)
-
- | (loop_1
- | stmt_1
- | (loop_2 stmt_3 stmt_4
- | (loop_4 stmt_5 stmt_6)
- | stmt_7
- | )
- | stmt_2
- | )
-
- lst_project_loop (loop_2, loop_4, stride)
-
- | (loop_1
- | stmt_1
- | (loop_2 stmt_3 stmt_4 stmt_5 stmt_6 stmt_7)
- | stmt_2
- | )
-
- lst_project_loop (loop_1, loop_2, stride)
-
- | (loop_1
- | stmt_1 stmt_3 stmt_4 stmt_5 stmt_6 stmt_7 stmt_2
- | )
-
- At each step, the iteration domain of the outer loop is enlarged to
- contain enough points to iterate over the inner loop domain. */
-
-/* Initializes RES to the number of iterations of the linearized loop
- LST. RES is the cardinal of the iteration domain of LST. */
-
-static void
-lst_linearized_niter (lst_p lst, mpz_t res)
-{
- int i;
- lst_p l;
- mpz_t n;
-
- mpz_init (n);
- mpz_set_si (res, 0);
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
- if (LST_LOOP_P (l))
- {
- lst_linearized_niter (l, n);
- mpz_add (res, res, n);
- }
-
- if (LST_LOOP_P (lst))
- {
- lst_niter_for_loop (lst, n);
-
- if (mpz_cmp_si (res, 0) != 0)
- mpz_mul (res, res, n);
- else
- mpz_set (res, n);
- }
-
- mpz_clear (n);
-}
-
-/* Applies the translation "f (x) = x + OFFSET" to the loop containing
- STMT. */
-
-static void
-lst_offset (lst_p stmt, mpz_t offset)
-{
- lst_p inner = LST_LOOP_FATHER (stmt);
- poly_bb_p pbb = LST_PBB (stmt);
- ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
- int inner_depth = lst_depth (inner);
- ppl_dimension_type inner_dim = psct_dynamic_dim (pbb, inner_depth);
- ppl_Linear_Expression_t expr;
- ppl_dimension_type dim;
- ppl_Coefficient_t one;
- mpz_t x;
-
- mpz_init (x);
- mpz_set_si (x, 1);
- ppl_new_Coefficient (&one);
- ppl_assign_Coefficient_from_mpz_t (one, x);
-
- ppl_Polyhedron_space_dimension (poly, &dim);
- ppl_new_Linear_Expression_with_dimension (&expr, dim);
-
- ppl_set_coef (expr, inner_dim, 1);
- ppl_set_inhomogeneous_gmp (expr, offset);
- ppl_Polyhedron_affine_image (poly, inner_dim, expr, one);
- ppl_delete_Linear_Expression (expr);
- ppl_delete_Coefficient (one);
-}
-
-/* Scale by FACTOR the loop LST containing STMT. */
-
-static void
-lst_scale (lst_p lst, lst_p stmt, mpz_t factor)
-{
- mpz_t x;
- ppl_Coefficient_t one;
- int outer_depth = lst_depth (lst);
- poly_bb_p pbb = LST_PBB (stmt);
- ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
- ppl_dimension_type outer_dim = psct_dynamic_dim (pbb, outer_depth);
- ppl_Linear_Expression_t expr;
- ppl_dimension_type dim;
-
- mpz_init (x);
- mpz_set_si (x, 1);
- ppl_new_Coefficient (&one);
- ppl_assign_Coefficient_from_mpz_t (one, x);
-
- ppl_Polyhedron_space_dimension (poly, &dim);
- ppl_new_Linear_Expression_with_dimension (&expr, dim);
-
- /* outer_dim = factor * outer_dim. */
- ppl_set_coef_gmp (expr, outer_dim, factor);
- ppl_Polyhedron_affine_image (poly, outer_dim, expr, one);
- ppl_delete_Linear_Expression (expr);
-
- mpz_clear (x);
- ppl_delete_Coefficient (one);
-}
-
-/* Project the INNER loop into the iteration domain of the OUTER loop.
- STRIDE is the number of iterations between two iterations of the
- outer loop. */
-
-static void
-lst_project_loop (lst_p outer, lst_p inner, mpz_t stride)
-{
- int i;
- lst_p stmt;
- mpz_t x;
- ppl_Coefficient_t one;
- int outer_depth = lst_depth (outer);
- int inner_depth = lst_depth (inner);
-
- mpz_init (x);
- mpz_set_si (x, 1);
- ppl_new_Coefficient (&one);
- ppl_assign_Coefficient_from_mpz_t (one, x);
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (inner), i, stmt)
- {
- poly_bb_p pbb = LST_PBB (stmt);
- ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
- ppl_dimension_type outer_dim = psct_dynamic_dim (pbb, outer_depth);
- ppl_dimension_type inner_dim = psct_dynamic_dim (pbb, inner_depth);
- ppl_Linear_Expression_t expr;
- ppl_dimension_type dim;
- ppl_dimension_type *ds;
-
- /* There should be no loops under INNER. */
- gcc_assert (!LST_LOOP_P (stmt));
- ppl_Polyhedron_space_dimension (poly, &dim);
- ppl_new_Linear_Expression_with_dimension (&expr, dim);
-
- /* outer_dim = outer_dim * stride + inner_dim. */
- ppl_set_coef (expr, inner_dim, 1);
- ppl_set_coef_gmp (expr, outer_dim, stride);
- ppl_Polyhedron_affine_image (poly, outer_dim, expr, one);
- ppl_delete_Linear_Expression (expr);
-
- /* Project on inner_dim. */
- ppl_new_Linear_Expression_with_dimension (&expr, dim - 1);
- ppl_Polyhedron_affine_image (poly, inner_dim, expr, one);
- ppl_delete_Linear_Expression (expr);
-
- /* Remove inner loop and the static schedule of its body. */
- /* FIXME: As long as we use PPL we are not able to remove the old
- scattering dimensions. The reason is that these dimensions are not
- entirely unused. They are not necessary as part of the scheduling
- vector, as the earlier dimensions already unambiguously define the
- execution time, however they may still be needed to carry modulo
- constraints as introduced e.g. by strip mining. The correct solution
- would be to project these dimensions out of the scattering polyhedra.
- In case they are still required to carry modulo constraints they should be kept
- internally as existentially quantified dimensions. PPL does only support
- projection of rational polyhedra, however in this case we need an integer
- projection. With isl this will be trivial to implement. For now we just
- leave the dimensions. This is a little ugly, but should be correct. */
- if (0) {
- ds = XNEWVEC (ppl_dimension_type, 2);
- ds[0] = inner_dim;
- ds[1] = inner_dim + 1;
- ppl_Polyhedron_remove_space_dimensions (poly, ds, 2);
- PBB_NB_SCATTERING_TRANSFORM (pbb) -= 2;
- free (ds);
- }
- }
-
- mpz_clear (x);
- ppl_delete_Coefficient (one);
-}
-
-/* Flattens the loop nest LST. Return true when something changed.
- OFFSET is used to compute the number of iterations of the outermost
- loop before the current LST is executed. */
-
-static bool
-lst_flatten_loop (lst_p lst, mpz_t init_offset)
-{
- int i;
- lst_p l;
- bool res = false;
- mpz_t n, one, offset, stride;
-
- mpz_init (n);
- mpz_init (one);
- mpz_init (offset);
- mpz_init (stride);
- mpz_set (offset, init_offset);
- mpz_set_si (one, 1);
-
- lst_linearized_niter (lst, stride);
- lst_niter_for_loop (lst, n);
- mpz_tdiv_q (stride, stride, n);
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
- if (LST_LOOP_P (l))
- {
- res = true;
-
- lst_flatten_loop (l, offset);
- lst_niter_for_loop (l, n);
-
- lst_project_loop (lst, l, stride);
-
- /* The offset is the number of iterations minus 1, as we want
- to execute the next statements at the same iteration as the
- last iteration of the loop. */
- mpz_sub (n, n, one);
- mpz_add (offset, offset, n);
- }
- else
- {
- lst_scale (lst, l, stride);
- if (mpz_cmp_si (offset, 0) != 0)
- lst_offset (l, offset);
- }
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
- if (LST_LOOP_P (l))
- lst_remove_loop_and_inline_stmts_in_loop_father (l);
-
- mpz_clear (n);
- mpz_clear (one);
- mpz_clear (offset);
- mpz_clear (stride);
- return res;
-}
-
-/* Remove all but the first 3 dimensions of the scattering:
- - dim0: the static schedule for the loop
- - dim1: the dynamic schedule of the loop
- - dim2: the static schedule for the loop body. */
-
-static void
-remove_unused_scattering_dimensions (lst_p lst)
-{
- int i;
- lst_p stmt;
- mpz_t x;
- ppl_Coefficient_t one;
-
- mpz_init (x);
- mpz_set_si (x, 1);
- ppl_new_Coefficient (&one);
- ppl_assign_Coefficient_from_mpz_t (one, x);
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, stmt)
- {
- poly_bb_p pbb = LST_PBB (stmt);
- ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
- int j, nb_dims_to_remove = PBB_NB_SCATTERING_TRANSFORM (pbb) - 3;
- ppl_dimension_type *ds;
-
- /* There should be no loops inside LST after flattening. */
- gcc_assert (!LST_LOOP_P (stmt));
-
- if (!nb_dims_to_remove)
- continue;
-
- ds = XNEWVEC (ppl_dimension_type, nb_dims_to_remove);
- for (j = 0; j < nb_dims_to_remove; j++)
- ds[j] = j + 3;
-
- ppl_Polyhedron_remove_space_dimensions (poly, ds, nb_dims_to_remove);
- PBB_NB_SCATTERING_TRANSFORM (pbb) -= nb_dims_to_remove;
- free (ds);
- }
-
- mpz_clear (x);
- ppl_delete_Coefficient (one);
-}
-
-/* Flattens all the loop nests of LST. Return true when something
- changed. */
-
-static bool
-lst_do_flatten (lst_p lst)
-{
- int i;
- lst_p l;
- bool res = false;
- mpz_t zero;
-
- if (!lst
- || !LST_LOOP_P (lst))
- return false;
-
- mpz_init (zero);
- mpz_set_si (zero, 0);
-
- FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
- if (LST_LOOP_P (l))
- {
- res |= lst_flatten_loop (l, zero);
-
- /* FIXME: As long as we use PPL we are not able to remove the old
- scattering dimensions. The reason is that these dimensions are not
- entirely unused. They are not necessary as part of the scheduling
- vector, as the earlier dimensions already unambiguously define the
- execution time, however they may still be needed to carry modulo
- constraints as introduced e.g. by strip mining. The correct solution
- would be to project these dimensions out of the scattering polyhedra.
- In case they are still required to carry modulo constraints they should be kept
- internally as existentially quantified dimensions. PPL does only support
- projection of rational polyhedra, however in this case we need an integer
- projection. With isl this will be trivial to implement. For now we just
- leave the dimensions. This is a little ugly, but should be correct. */
- if (0)
- remove_unused_scattering_dimensions (l);
- }
-
- lst_update_scattering (lst);
- mpz_clear (zero);
- return res;
-}
-
-/* Flatten all the loop nests in SCOP. Returns true when something
- changed. */
-
-bool
-flatten_all_loops (scop_p scop)
-{
- return lst_do_flatten (SCOP_TRANSFORMED_SCHEDULE (scop));
-}
-
-#endif
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