Re: [patch] Fix PR middle-end/82569

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Oct 23, 2017 at 12:57 PM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
> this is the regression present on the mainline for Power6 and introduced by my
> patch fiddling with SUBREG_PROMOTED_VAR_P in expand_expr_real_1.  It turns out
> that the ouf-of-ssa pass implicitly assumes that promoted RTXes for partitions
> are fully initialized (because it can generate direct moves in promoted mode)
> and clearing SUBREG_PROMOTED_VAR_P for some of them goes against this.
>
> Therefore the attached patch goes in the opposite direction and initializes
> the RTXes for problematic partitions on function entry.  Surprisingly enough,
> this generates smaller code on average at -O2 for gcc.c-torture/compile:
>
>  49 files changed, 1243 insertions(+), 1694 deletions(-)
>
> probably because the compiler can now infer values on paths from entry where
> variables are uninitialized.  Tested on PowerPC64/Linux, OK for the mainline?

Ok.

Thanks,
Richard.


>
> 2017-10-23  Eric Botcazou  <ebotcazou@adacore.com>
>
>         PR middle-end/82569
>         * tree-outof-ssa.h (always_initialized_rtx_for_ssa_name_p): Delete.
>         * expr.c (expand_expr_real_1) <expand_decl_rtl>: Revert latest change.
>         * loop-iv.c (iv_get_reaching_def): Likewise.
>         * cfgexpand.c (expand_one_ssa_partition): Initialize the RTX if the
>         variable is promoted and the partition contains undefined values.
>
> --
> Eric Botcazou