[PATCH] Improve overhead of tree-affine.c a bit

[Richard Biener]

When working on PR63184 I noticed that tree-affine.c is still one of
the gimple_assign_rhs_to_tree callers and does so quite aggressively
for no good reason.  The following restricts it to the cases we
handle in tree_to_aff_combination, axing one unreachable case.
It also makes sure to cache expanded combinations with SSA names
as keys rather than a GENERIC conversion tree which isn't shared
anyways.

Bootstrapped and tested on x86_64-unknown-linux-gnu, object files
in gcc/ are the same patched/unpatched with the exception of
tree-affine.o.

Applied to trunk.

Richard.

2018-12-10  Richard Biener  <rguent...@suse.de>

        * tree-affine.c (tree_to_aff_combination): Remove unreachable
        MEM_REF case.
        (aff_combination_expand): Cache on SSA names, not possibly
        on conversion trees.  Avoid expanding cases we do not handle.

diff --git a/gcc/tree-affine.c b/gcc/tree-affine.c
index 96b479dfc4c..41c52ab468d 100644
--- a/gcc/tree-affine.c
+++ b/gcc/tree-affine.c
@@ -351,6 +351,7 @@ tree_to_aff_combination (tree expr, tree type, aff_tree 
*comb)
       return;
 
     case MEM_REF:
+      gcc_unreachable ();
       if (TREE_CODE (TREE_OPERAND (expr, 0)) == ADDR_EXPR)
        tree_to_aff_combination (TREE_OPERAND (TREE_OPERAND (expr, 0), 0),
                                 type, comb);
@@ -721,21 +722,39 @@ aff_combination_expand (aff_tree *comb ATTRIBUTE_UNUSED,
       if (TREE_CODE_CLASS (code) == tcc_reference)
        continue;
 
-      if (!*cache)
-       *cache = new hash_map<tree, name_expansion *>;
-      name_expansion **slot = &(*cache)->get_or_insert (e);
-      exp = *slot;
-
+      name_expansion **slot = NULL;
+      if (*cache)
+       slot = (*cache)->get (name);
+      exp = slot ? *slot : NULL;
       if (!exp)
        {
+         /* Only bother to handle cases tree_to_aff_combination will.  */
+         switch (code)
+           {
+           case POINTER_PLUS_EXPR:
+           case PLUS_EXPR:
+           case MINUS_EXPR:
+           case MULT_EXPR:
+           case NEGATE_EXPR:
+           case BIT_NOT_EXPR:
+           CASE_CONVERT:
+             rhs = gimple_assign_rhs_to_tree (def);
+             break;
+           case ADDR_EXPR:
+           case INTEGER_CST:
+           case POLY_INT_CST:
+             rhs = gimple_assign_rhs1 (def);
+             break;
+           default:
+             continue;
+           }
+         tree_to_aff_combination (rhs, TREE_TYPE (name), &current);
          exp = XNEW (struct name_expansion);
          exp->in_progress = 1;
-         *slot = exp;
-         rhs = gimple_assign_rhs_to_tree (def);
-         if (e != name)
-           rhs = fold_convert (type, rhs);
-
-         tree_to_aff_combination_expand (rhs, comb->type, &current, cache);
+         if (!*cache)
+           *cache = new hash_map<tree, name_expansion *>;
+         (*cache)->put (name, exp);
+         aff_combination_expand (&current, cache);
          exp->expansion = current;
          exp->in_progress = 0;
        }
@@ -746,6 +765,8 @@ aff_combination_expand (aff_tree *comb ATTRIBUTE_UNUSED,
          gcc_assert (!exp->in_progress);
          current = exp->expansion;
        }
+      if (!useless_type_conversion_p (comb->type, current.type))
+       aff_combination_convert (&current, comb->type);
 
       /* Accumulate the new terms to TO_ADD, so that we do not modify
         COMB while traversing it; include the term -coef * E, to remove