On Mon, 8 Aug 2016, Jakub Jelinek wrote:
> Hi!
>
> Only +0.0 stores can be optimized into memset, -0.0 can't, so if we are
> honoring signed zeros, we should make sure the constant is positive.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Hmm, I don't think we should see -0.0 as +0.0 with -fno-signed-zeros.
As far as I can see this is a memory load/store op and we may not
transform, say,
double x = a[i];
b[i] = x;
into a copy that changes -0.0 to +0.0. loop distribution looks for
a value with all-zero bytes.
Richard.
> 2016-08-08 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/72824
> * tree-loop-distribution.c (const_with_all_bytes_same): If honoring
> signed zeros, verify real_zerop is not negative.
>
> * gcc.c-torture/execute/ieee/pr72824.c: New test.
>
> --- gcc/tree-loop-distribution.c.jj 2016-07-16 10:41:04.000000000 +0200
> +++ gcc/tree-loop-distribution.c 2016-08-07 13:55:19.704681784 +0200
> @@ -750,12 +750,40 @@ const_with_all_bytes_same (tree val)
> int i, len;
>
> if (integer_zerop (val)
> - || real_zerop (val)
> || (TREE_CODE (val) == CONSTRUCTOR
> && !TREE_CLOBBER_P (val)
> && CONSTRUCTOR_NELTS (val) == 0))
> return 0;
>
> + if (real_zerop (val))
> + {
> + if (!HONOR_SIGNED_ZEROS (val))
> + return 0;
> + /* If honoring signed zeros, only return 0 for +0.0, not for -0.0. */
> + switch (TREE_CODE (val))
> + {
> + case REAL_CST:
> + if (!real_isneg (TREE_REAL_CST_PTR (val)))
> + return 0;
> + break;
> + case COMPLEX_CST:
> + if (!const_with_all_bytes_same (TREE_REALPART (val))
> + && !const_with_all_bytes_same (TREE_IMAGPART (val)))
> + return 0;
> + break;
> + case VECTOR_CST:
> + unsigned int j;
> + for (j = 0; j < VECTOR_CST_NELTS (val); ++j)
> + if (const_with_all_bytes_same (val))
> + break;
> + if (j == VECTOR_CST_NELTS (val))
> + return 0;
> + break;
> + default:
> + break;
> + }
> + }
> +
> if (CHAR_BIT != 8 || BITS_PER_UNIT != 8)
> return -1;
>
> --- gcc/testsuite/gcc.c-torture/execute/ieee/pr72824.c.jj 2016-08-07
> 13:19:42.443863775 +0200
> +++ gcc/testsuite/gcc.c-torture/execute/ieee/pr72824.c 2016-08-07
> 13:19:35.034958218 +0200
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/72824 */
> +
> +static inline void
> +foo (float *x, float value)
> +{
> + int i;
> + for (i = 0; i < 32; ++i)
> + x[i] = value;
> +}
> +
> +int
> +main ()
> +{
> + float x[32];
> + foo (x, -0.f);
> + if (__builtin_copysignf (1.0, x[3]) != -1.0f)
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
