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[GSoC] generation of GCC expression trees from isl ast expressions

Hi Tobias,

I'm currently working on generation of GCC expression trees from isl
ast expressions . Could you please answer a few questions about it?

1. How is it better to generate tree from isl_ast_expr_int? In the
temporary variant I call isl_ast_expr_get_int to get isl_int from
isl_ast_expr. After this, gmp_cst_to_tree (it was used in
graphite-clast-to-gimple.c) is called to generate tree frome isl_int.
It is possible now, because isl_int is mpz_t. However, it can be
changed in the future, according to comments from its source code.

+/* Converts a GMP constant VAL to a tree and returns it.  */
+static tree
+gmp_cst_to_tree (tree type, mpz_t val)
+  tree t = type ? type : integer_type_node;
+  mpz_t tmp;
+  mpz_init (tmp);
+  mpz_set (tmp, val);
+  wide_int wi = wi::from_mpz (t, tmp, true);
+  mpz_clear (tmp);
+  return wide_int_to_tree (t, wi);

+/* Converts a isl_ast_expr_int expression E to a GCC expression tree of
+   type TYPE.  */
+static tree
+gcc_expression_from_isl_expr_int (tree type, __isl_keep isl_ast_expr *expr)
+  gcc_assert (isl_ast_expr_get_type (expr) == isl_ast_expr_int);
+  isl_int val;
+  isl_int_init (val);
+  if (isl_ast_expr_get_int (expr, &val) == -1)
+    {
+      isl_int_clear (val);
+      return NULL_TREE;
+    }
+  else
+    return gmp_cst_to_tree (type, val);

2. As you said in previous messages, we can always use signed 64/128,
until isl is able to give information about types. I haven't found
them in types of Generic
( Could they
be declared using build_nonstandard_integer_type (128, 1)?

3. If I am not mistaken, the structure ivs_params from
graphite-clast-to-gimple.c is used to store induction variables and
parameters, rename them according to SSA form. Could it be used in
graphite-isl-ast-to-gimple.c, too?

4. Should we transform all isl_ast_expr_op types of isl ast
expressions to GCC expression tree? For example, the following types
are not transformed at all in Polly project: isl_ast_op_cond,
isl_ast_op_and_then, isl_ast_op_or_else, isl_ast_op_call,
isl_ast_op_member, isl_ast_op_access, isl_ast_op_pdiv_q,
isl_ast_op_pdiv_r, isl_ast_op_div, isl_ast_op_fdiv_q.

The first draft of generation of GCC expression trees from isl ast
expressions can be found below:

                                   Cheers, Roman Gareev

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