Great, thanks! Results are good on this specific test case. Seems like
a nice thing to add in 4.8.
On Fri, 2012-01-27 at 18:40 +0100, Michael Matz wrote:
> Hi,
>
> On Fri, 27 Jan 2012, William J. Schmidt wrote:
>
> > ------------------------------------------------------------------------
> > int
> > test_switch_1 (unsigned int *index, int i)
> > {
> > switch (*index)
> ...
> > However, for the first case, temporary expression replacement has
> > effectively removed the assignment to D.2004_3 (single local immediate
> > use permits replacement), so instead we see:
> >
> > ------------------------------------------------------------------------
> > ;; switch (D.2004_3) <default: <L3>, case 0: <L5>, case 1: <L1>, case 2:
> > <L2>>
> >
> > (insn 7 6 8 (set (reg:SI 124)
> > (mem:SI (reg/v/f:SI 122 [ index ]) [2 *index_2(D)+0 S4 A32]))
> > t1.i:4 -1
>
> With TER there is no decl anymore to associate the pseudo with.
> Conceptually, what's expanded is "*index", not an assignment to a pseudo.
> The move into a pseudo (and the creation of that very pseudo) is done by
> copy_to_reg in expand_case.
>
> > It would be a nice enhancement if the REG_EXPR could be preserved in
> > such cases. Does anyone know if there's something that would prevent
> > this?
>
> The hack below works in this specific situation (TERed into a switch), and
> adds a REG_EXPR when an TERed SSA name ever expanded into a pseudo (i.e.
> also for some more generic situations).
>
>
> Ciao,
> Michael.
> Index: expr.c
> ===================================================================
> --- expr.c (revision 183559)
> +++ expr.c (working copy)
> @@ -8991,8 +8991,13 @@ expand_expr_real_1 (tree exp, rtx target
> && stmt_is_replaceable_p (SSA_NAME_DEF_STMT (exp)))
> g = SSA_NAME_DEF_STMT (exp);
> if (g)
> - return expand_expr_real (gimple_assign_rhs_to_tree (g), target, tmode,
> - modifier, NULL);
> + {
> + rtx r = expand_expr_real (gimple_assign_rhs_to_tree (g), target,
> + tmode, modifier, NULL);
> + if (REG_P (r) && !REG_EXPR (r))
> + set_reg_attrs_for_decl_rtl (SSA_NAME_VAR (exp), r);
> + return r;
> + }
>
> ssa_name = exp;
> decl_rtl = get_rtx_for_ssa_name (ssa_name);
> Index: stmt.c
> ===================================================================
> --- stmt.c (revision 183559)
> +++ stmt.c (working copy)
> @@ -2381,7 +2381,11 @@ expand_case (gimple stmt)
> do_pending_stack_adjust ();
>
> if (MEM_P (index))
> - index = copy_to_reg (index);
> + {
> + index = copy_to_reg (index);
> + if (TREE_CODE (index_expr) == SSA_NAME)
> + set_reg_attrs_for_decl_rtl (SSA_NAME_VAR (index_expr), index);
> + }
>
> /* We generate a binary decision tree to select the
> appropriate target code. This is done as follows:
>
