On Tue, Aug 09, 2016 at 08:53:54AM +0200, Richard Biener wrote:
> 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.
So shall I just drop the if (!HONOR_SIGNED_ZEROS (val)) return 0; from the
patch? With that removed, it will not transform b[i] = -0.0; into
memset (b, 0, ...); even with -fno-signed-zeros.
> > 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;
> >
Jakub
