On Wed, 18 May 2016, Richard Biener wrote:
The following adjusts get_alias_set beahvior when applied to
union accesses to use the union alias-set rather than alias-set
zero. This is in line with behavior from the alias oracle
which (bogously) circumvents alias-set zero with looking at
the alias-sets of the base object. Thus for
union U { int i; float f; };
float
foo (union U *u, double *p)
{
u->f = 1.;
*p = 0;
return u->f;
}
the langhooks ensured u->f has alias-set zero and thus disambiguation
against *p was not allowed. Still the alias-oracle did the disambiguation
by using the alias set of the union here (I think optimizing the
return to return 1. is valid).
We have a good place in the middle-end to apply such rules which
is component_uses_parent_alias_set_from - this is where I move
the logic that is duplicated in various frontends.
The Java and Ada frontends do not allow union type punning (LTO does),
so this patch may eventually pessimize them. I don't care anything
about Java but Ada folks might want to chime in.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
Ok for trunk?
Ping.
Thanks,
Richard.
Thanks,
Richard.
2016-05-18 Richard Biener <rguenther@suse.de>
* alias.c (component_uses_parent_alias_set_from): Handle
type punning through union accesses by using the union alias set.
* gimple.c (gimple_get_alias_set): Remove union type punning case.
c-family/
* c-common.c (c_common_get_alias_set): Remove union type punning case.
fortran/
* f95-lang.c (LANG_HOOKS_GET_ALIAS_SET): Remove (un-)define.
(gfc_get_alias_set): Remove.