[PATCH GCC8][30/33]Fold more type conversion into binary arithmetic operations

[Richard Biener]

On Tue, Apr 18, 2017 at 12:53 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> Hi,
> Simplification of (T1)(X *+- CST) is already implemented in aff_combination_expand,
> this patch moves it to tree_to_aff_combination.  It also supports unsigned types
> if range information allows the transformation, as well as special case (T1)(X + X).
> Is it OK?

Can you first please simply move it?

+           /* In case X's type has wrapping overflow behavior, we can still
+              convert (T1)(X - CST) into (T1)X - (T1)CST if X - CST doesn't
+              overflow by range information.  Also Convert (T1)(X + CST) as
+              if it's (T1)(X - (-CST)).  */
+           if (TYPE_UNSIGNED (itype)
+               && TYPE_OVERFLOW_WRAPS (itype)
+               && TREE_CODE (op0) == SSA_NAME
+               && TREE_CODE (op1) == INTEGER_CST
+               && (icode == PLUS_EXPR || icode == MINUS_EXPR)
+               && get_range_info (op0, &minv, &maxv) == VR_RANGE)
+             {
+               if (icode == PLUS_EXPR)
+                 op1 = fold_build1 (NEGATE_EXPR, itype, op1);

Negating -INF will produce -INF(OVF) which we don't want to have in our IL,
I suggest to use

                  op1 = wide_int_to_tree (itype, wi::neg (op1));

instead.

+               if (wi::geu_p (minv, op1))
+                 {
+                   op0 = fold_convert (otype, op0);
+                   op1 = fold_convert (otype, op1);
+                   expr = fold_build2 (MINUS_EXPR, otype, op0, op1);
+                   tree_to_aff_combination (expr, type, comb);
+                   return;
+                 }
+             }

I think this is similar to a part of what Robin Dapp (sp?) is
proposing as fix for PR69526?

The same trick should work for (int)((unsigned)X - CST) with different
overflow checks
(you need to make sure the resulting expr does not overflow).

Richard.


> Thanks,
> bin
> 2017-04-11  Bin Cheng  <bin.cheng@arm.com>
>
>         * tree-affine.c: Include header file.
>         (aff_combination_expand): Move (T1)(X *+- CST) simplification to ...
>         (tree_to_aff_combination): ... here.  Support (T1)(X + X) case, and
>         unsigned type case if range information allows.