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

Message ID 20180327091817.GY8577@tucnak
State New
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  • [C++] Improve cp_fold on vector CONSTRUCTORs (PR c++/85077)
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Commit Message

Jakub Jelinek March 27, 2018, 9:18 a.m.
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.


	Jakub

Comments

Jason Merrill March 27, 2018, 7:52 p.m. | #1
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

Patch

--- 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" } }