[C++ PATCH] Improve cp_fold on vector CONSTRUCTORs (PR c++/85077)

[C++ PATCH] Improve cp_fold on vector CONSTRUCTORs (PR c++/85077)

[Jakub Jelinek]

Hi!

The following testcase regressed for 8+, because we delayed folding in
SAVE_EXPRs and end up passing a CONSTRUCTOR with V4SFmode and 4x 0.0
constants in it rather than a VECTOR_CST to the middle-end folder, which
uses real_zerop and thus doesn't recognize the CONSTRUCTOR in
VEC_COND_EXPR <x < { 0, 0, 0, 0 } ? -x : x> as zero and doesn't fold
it into ABS_EXPR.

We really should move that folding into match.pd, but that is a GCC 9 task.

Fixed by using fold on vector CONSTRUCTORs, the only thing fold does on
those is exactly the CONSTRUCTOR -> VECTOR_CST folding when possible.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2018-03-27  Jakub Jelinek  <jakub@redhat.com>

	PR c++/85077
	* cp-gimplify.c (cp_fold) <case CONSTRUCTOR>: For ctors with vector
	type call fold to generate VECTOR_CSTs when possible.

	* g++.dg/ext/vector35.C: New test.

--- gcc/cp/cp-gimplify.c.jj	2018-03-20 22:05:57.023431462 +0100
+++ gcc/cp/cp-gimplify.c	2018-03-26 16:08:47.728347579 +0200
@@ -2504,6 +2504,8 @@ cp_fold (tree x)
 	    CONSTRUCTOR_PLACEHOLDER_BOUNDARY (x)
 	      = CONSTRUCTOR_PLACEHOLDER_BOUNDARY (org_x);
 	  }
+	if (VECTOR_TYPE_P (TREE_TYPE (x)))
+	  x = fold (x);
 	break;
       }
     case TREE_VEC:
--- gcc/testsuite/g++.dg/ext/vector35.C.jj	2018-03-26 16:19:39.330809031 +0200
+++ gcc/testsuite/g++.dg/ext/vector35.C	2018-03-26 16:33:43.997330748 +0200
@@ -0,0 +1,22 @@
+// PR c++/85077
+// { dg-do compile }
+// { dg-options "-Ofast -fdump-tree-forwprop1" }
+
+typedef float V __attribute__((vector_size (4 * sizeof (float))));
+typedef double W __attribute__((vector_size (2 * sizeof (double))));
+
+void
+foo (V *y)
+{
+  V x = *y;
+  *y = x < 0 ? -x : x;
+}
+
+void
+bar (W *y)
+{
+  W x = *y;
+  *y = x < 0 ? -x : x;
+}
+
+// { dg-final { scan-tree-dump-times "ABS_EXPR <" 2 "forwprop1" } }

	Jakub

Re: [C++ PATCH] Improve cp_fold on vector CONSTRUCTORs (PR c++/85077)

[Jason Merrill]

OK.

On Tue, Mar 27, 2018 at 5:18 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> The following testcase regressed for 8+, because we delayed folding in
> SAVE_EXPRs and end up passing a CONSTRUCTOR with V4SFmode and 4x 0.0
> constants in it rather than a VECTOR_CST to the middle-end folder, which
> uses real_zerop and thus doesn't recognize the CONSTRUCTOR in
> VEC_COND_EXPR <x < { 0, 0, 0, 0 } ? -x : x> as zero and doesn't fold
> it into ABS_EXPR.
>
> We really should move that folding into match.pd, but that is a GCC 9 task.
>
> Fixed by using fold on vector CONSTRUCTORs, the only thing fold does on
> those is exactly the CONSTRUCTOR -> VECTOR_CST folding when possible.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2018-03-27  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/85077
>         * cp-gimplify.c (cp_fold) <case CONSTRUCTOR>: For ctors with vector
>         type call fold to generate VECTOR_CSTs when possible.
>
>         * g++.dg/ext/vector35.C: New test.
>
> --- gcc/cp/cp-gimplify.c.jj     2018-03-20 22:05:57.023431462 +0100
> +++ gcc/cp/cp-gimplify.c        2018-03-26 16:08:47.728347579 +0200
> @@ -2504,6 +2504,8 @@ cp_fold (tree x)
>             CONSTRUCTOR_PLACEHOLDER_BOUNDARY (x)
>               = CONSTRUCTOR_PLACEHOLDER_BOUNDARY (org_x);
>           }
> +       if (VECTOR_TYPE_P (TREE_TYPE (x)))
> +         x = fold (x);
>         break;
>        }
>      case TREE_VEC:
> --- gcc/testsuite/g++.dg/ext/vector35.C.jj      2018-03-26 16:19:39.330809031 +0200
> +++ gcc/testsuite/g++.dg/ext/vector35.C 2018-03-26 16:33:43.997330748 +0200
> @@ -0,0 +1,22 @@
> +// PR c++/85077
> +// { dg-do compile }
> +// { dg-options "-Ofast -fdump-tree-forwprop1" }
> +
> +typedef float V __attribute__((vector_size (4 * sizeof (float))));
> +typedef double W __attribute__((vector_size (2 * sizeof (double))));
> +
> +void
> +foo (V *y)
> +{
> +  V x = *y;
> +  *y = x < 0 ? -x : x;
> +}
> +
> +void
> +bar (W *y)
> +{
> +  W x = *y;
> +  *y = x < 0 ? -x : x;
> +}
> +
> +// { dg-final { scan-tree-dump-times "ABS_EXPR <" 2 "forwprop1" } }
>
>         Jakub