On Mon, 26 Oct 2020, Jan Hubicka wrote:
> Hi,
> while looking for special cases of buitins I noticed that tree-ssa-ccp
> can use EAF_RETURNS_ARG. I wonder if same should be done by value
> numbering and other propagators....
The issue is that changing
q = memcpy (p, r);
.. use q ...
to
memcpy (p, r);
.. use p ..
is bad for RA so we generally do not want to copy-propagate
EAF_RETURNS_ARG. We eventually do want to optimize a following
if (q == p)
of course. And we eventually want to do the _reverse_ transform,
replacing
memcpy (p, r)
.. use p ..
with
tem = memcpy (p, r)
.. use tem ..
ISTR playing with patches doing all of the above, would need to dig
them out again. There's also a PR about this I think.
Bernd added some code to RTL call expansion, not sure exactly
what it does...
> Bootstrapped/regtested x86_64-linux, OK?
OK.
Thanks,
Richard.
> Honza
>
> * tree-ssa-ccp.c (evaluate_stmt): Use EAF_RETURNS_ARG; do not handle
> string buitings specially.
> diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
> index 0432fe5513d..ef44e66ce8b 100644
> --- a/gcc/tree-ssa-ccp.c
> +++ b/gcc/tree-ssa-ccp.c
> @@ -1796,6 +1796,7 @@ evaluate_stmt (gimple *stmt)
> ccp_lattice_t likelyvalue = likely_value (stmt);
> bool is_constant = false;
> unsigned int align;
> + bool ignore_return_flags = false;
>
> if (dump_file && (dump_flags & TDF_DETAILS))
> {
> @@ -1965,22 +1966,9 @@ evaluate_stmt (gimple *stmt)
> val.mask = ~((HOST_WIDE_INT) align / BITS_PER_UNIT - 1);
> break;
>
> - /* These builtins return their first argument, unmodified. */
> - case BUILT_IN_MEMCPY:
> - case BUILT_IN_MEMMOVE:
> - case BUILT_IN_MEMSET:
> - case BUILT_IN_STRCPY:
> - case BUILT_IN_STRNCPY:
> - case BUILT_IN_MEMCPY_CHK:
> - case BUILT_IN_MEMMOVE_CHK:
> - case BUILT_IN_MEMSET_CHK:
> - case BUILT_IN_STRCPY_CHK:
> - case BUILT_IN_STRNCPY_CHK:
> - val = get_value_for_expr (gimple_call_arg (stmt, 0), true);
> - break;
> -
> case BUILT_IN_ASSUME_ALIGNED:
> val = bit_value_assume_aligned (stmt, NULL_TREE, val, false);
> + ignore_return_flags = true;
> break;
>
> case BUILT_IN_ALIGNED_ALLOC:
> @@ -2049,6 +2037,15 @@ evaluate_stmt (gimple *stmt)
> if (attrs)
> val = bit_value_assume_aligned (stmt, attrs, val, true);
> }
> + int flags = ignore_return_flags
> + ? 0 : gimple_call_return_flags (as_a <gcall *> (stmt));
> + if (flags & ERF_RETURNS_ARG
> + && (flags & ERF_RETURN_ARG_MASK) < gimple_call_num_args (stmt))
> + {
> + val = get_value_for_expr
> + (gimple_call_arg (stmt,
> + flags & ERF_RETURN_ARG_MASK), true);
> + }
> }
> is_constant = (val.lattice_val == CONSTANT);
> }
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
