On Mon, Nov 29, 2021 at 1:57 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Sun, Nov 28, 2021 at 12:25 PM Jeff Law via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> >
> >
> > On 11/28/2021 10:56 AM, apinski--- via Gcc-patches wrote:
> > > From: Andrew Pinski <apin...@marvell.com>
> > >
> > > This just adds a simplification to simplify_vector_constructor for
> > > vector of 1 element to be VCE which should reduce memory usage in
> > > the compiler and maybe allow for some more optimizations.
> > >
> > > OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
> > >
> > > PR tree-optimization/101540
> > >
> > > gcc/ChangeLog:
> > >
> > > * tree-ssa-forwprop.c (simplify_vector_constructor):
> > > Simplify constructor of vector of 1 element to just
> > > be a VIEW_CONVERT_EXPR.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > * gcc.dg/tree-ssa/pr101540-1.c: New test.
> > So why generate a VCE here if the type conversion is useless? Why not
> > just a NOP_EXPR? Is there something special about converting between
> > the element type and the outer vector type that requires VCE rather than
> > NOP_EXR? Neither an ACK or NAK, just trying to understand it a bit better.
>
>
> Because right now tree-cfg.c has this check for vector types for NOP_EXPR:
> /* Allow conversions between vectors with the same number of elements,
> provided that the conversion is OK for the element types too. */
> if (VECTOR_TYPE_P (lhs_type)
> && VECTOR_TYPE_P (rhs1_type)
> && known_eq (TYPE_VECTOR_SUBPARTS (lhs_type),
> TYPE_VECTOR_SUBPARTS (rhs1_type)))
> {
> lhs_type = TREE_TYPE (lhs_type);
> rhs1_type = TREE_TYPE (rhs1_type);
> }
> else if (VECTOR_TYPE_P (lhs_type) || VECTOR_TYPE_P (rhs1_type))
> {
> error ("invalid vector types in nop conversion");
> debug_generic_expr (lhs_type);
> debug_generic_expr (rhs1_type);
> return true;
> }
>
> We can change this check here for NOP_EXPR and vector types but VCE is
> still a nop in most cases and handled as such really. But I wonder if
> the rest of the compiler is ready for it though.
It's definitely not a NOP, I think the original patch is OK.
Thanks,
Richard.
>
> Thanks,
> Andrew Pinski
>
> >
> > Jeff
> >
> >
