Re: [3/7] Optimize ZEXT_EXPR with tree-vrp

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Sep 7, 2015 at 4:58 AM, Kugan <kugan.vivekanandarajah@linaro.org> wrote:
> This patch tree-vrp handling and optimization for ZEXT_EXPR.

+  else if (code == SEXT_EXPR)
+    {
+      gcc_assert (range_int_cst_p (&vr1));
+      unsigned int prec = tree_to_uhwi (vr1.min);
+      type = vr0.type;
+      wide_int tmin, tmax;
+      wide_int type_min, type_max;
+      wide_int may_be_nonzero, must_be_nonzero;
+
+      gcc_assert (!TYPE_UNSIGNED (expr_type));

hmm, I don't think we should restrict SEXT_EXPR this way.  SEXT_EXPR
should operate on both signed and unsigned types and the result type
should be the same as the type of operand 0.

+      type_min = wi::shwi (1 << (prec - 1),
+                          TYPE_PRECISION (TREE_TYPE (vr0.min)));
+      type_max = wi::shwi (((1 << (prec - 1)) - 1),
+                          TYPE_PRECISION (TREE_TYPE (vr0.max)));

there is wi::min_value and max_value for this.

+         HOST_WIDE_INT int_may_be_nonzero = may_be_nonzero.to_uhwi ();
+         HOST_WIDE_INT int_must_be_nonzero = must_be_nonzero.to_uhwi ();

this doesn't need to fit a HOST_WIDE_INT, please use wi::bit_and (can't
find a test_bit with a quick search).

+      tmin = wi::sext (tmin, prec - 1);
+      tmax = wi::sext (tmax, prec - 1);
+      min = wide_int_to_tree (expr_type, tmin);
+      max = wide_int_to_tree (expr_type, tmax);

not sure why you need the extra sign-extensions here.

+    case SEXT_EXPR:
+       {
+         gcc_assert (is_gimple_min_invariant (op1));
+         unsigned int prec = tree_to_uhwi (op1);

no need to assert, tree_to_uhwi will do that for you.

+         HOST_WIDE_INT may_be_nonzero = may_be_nonzero0.to_uhwi ();
+         HOST_WIDE_INT must_be_nonzero = must_be_nonzero0.to_uhwi ();

likewise with HOST_WIDE__INT issue.

Otherwise looks ok to me.  Btw, this and adding of SEXT_EXPR could be
accompanied with a match.pd pattern detecting sign-extension patterns,
that would give some extra test coverage.

Thanks,
Richard.

>
>
> gcc/ChangeLog:
>
> 2015-09-07  Kugan Vivekanandarajah  <kuganv@linaro.org>
>
>         * tree-vrp.c (extract_range_from_binary_expr_1): Handle SEXT_EXPR.
>         (simplify_bit_ops_using_ranges): Likewise.
>         (simplify_stmt_using_ranges): Likewise.