Split can_vec_perm_p into can_vec_perm_{var,const}_p

This patch splits can_vec_perm_p into two functions: can_vec_perm_var_p
for testing permute operations with variable selection vectors, and
can_vec_perm_const_p for testing permute operations with specific
constant selection vectors.  This means that we can pass the constant
selection vector by reference.

Constant permutes can still use a variable permute as a fallback.
A later patch adds a check to makre sure that we don't truncate the
vector indices when doing this.

However, have_whole_vector_shift checked:

  if (direct_optab_handler (vec_perm_const_optab, mode) == CODE_FOR_nothing)
    return false;

which had the effect of disallowing the fallback to variable permutes.
I'm not sure whether that was the intention or whether it was just
supposed to short-cut the loop on targets that don't support permutes.
(But then why bother?  The first check in the loop would fail and
we'd bail out straightaway.)

The patch adds a parameter for disallowing the fallback.  I think it
makes sense to do this for the following code in the VEC_PERM_EXPR
folder:

	  /* Some targets are deficient and fail to expand a single
	     argument permutation while still allowing an equivalent
	     2-argument version.  */
	  if (need_mask_canon && arg2 == op2
	      && !can_vec_perm_p (TYPE_MODE (type), false, &sel)
	      && can_vec_perm_p (TYPE_MODE (type), false, &sel2))

since it's really testing whether the expand_vec_perm_const code expects
a particular form.

2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* optabs-query.h (can_vec_perm_p): Delete.
	(can_vec_perm_var_p, can_vec_perm_const_p): Declare.
	* optabs-query.c (can_vec_perm_p): Split into...
	(can_vec_perm_var_p, can_vec_perm_const_p): ...these two functions.
	(can_mult_highpart_p): Use can_vec_perm_const_p to test whether a
	particular selector is valid.
	* tree-ssa-forwprop.c (simplify_vector_constructor): Likewise.
	* tree-vect-data-refs.c (vect_grouped_store_supported): Likewise.
	(vect_grouped_load_supported): Likewise.
	(vect_shift_permute_load_chain): Likewise.
	* tree-vect-slp.c (vect_build_slp_tree_1): Likewise.
	(vect_transform_slp_perm_load): Likewise.
	* tree-vect-stmts.c (perm_mask_for_reverse): Likewise.
	(vectorizable_bswap): Likewise.
	(vect_gen_perm_mask_checked): Likewise.
	* fold-const.c (fold_ternary_loc): Likewise.  Don't take
	implementations of variable permutation vectors into account
	when deciding which selector to use.
	* tree-vect-loop.c (have_whole_vector_shift): Don't check whether
	vec_perm_const_optab is supported; instead use can_vec_perm_const_p
	with a false third argument.
	* tree-vect-generic.c (lower_vec_perm): Use can_vec_perm_const_p
	to test whether the constant selector is valid and can_vec_perm_var_p
	to test whether a variable selector is valid.

From-SVN: r256091

1 files changed, 2 insertions, 2 deletions

diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c
index c225814..7e78df8 100644
--- a/gcc/tree-vect-generic.c
+++ b/gcc/tree-vect-generic.c
@@ -1306,7 +1306,7 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
 	sel_int.quick_push (TREE_INT_CST_LOW (VECTOR_CST_ELT (mask, i))
 			    & (2 * elements - 1));
 
-      if (can_vec_perm_p (TYPE_MODE (vect_type), false, &sel_int))
+      if (can_vec_perm_const_p (TYPE_MODE (vect_type), sel_int))
 	{
 	  gimple_assign_set_rhs3 (stmt, mask);
 	  update_stmt (stmt);
@@ -1337,7 +1337,7 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
 	    }
 	}
     }
-  else if (can_vec_perm_p (TYPE_MODE (vect_type), true, NULL))
+  else if (can_vec_perm_var_p (TYPE_MODE (vect_type)))
     return;
   
   warning_at (loc, OPT_Wvector_operation_performance,