--- /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 "tm.h"
+#include "ggc.h"
+#include "tree.h"
+#include "rtl.h"
+#include "output.h"
+#include "basic-block.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "toplev.h"
+#include "tree-dump.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "tree-chrec.h"
+#include "tree-data-ref.h"
+#include "tree-scalar-evolution.h"
+#include "tree-pass.h"
+#include "domwalk.h"
+#include "value-prof.h"
+#include "pointer-set.h"
+#include "gimple.h"
+#include "params.h"
+
+#ifdef HAVE_cloog
+#include "ppl_c.h"
+#include "sese.h"
+#include "graphite-ppl.h"
+#include "graphite.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 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 nests 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 such that it
+
+ 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. */
+ 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);
+ 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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