On Mon, Apr 9, 2012 at 8:37 AM, Alexandre Oliva <aol...@redhat.com> wrote:
> On Jun  3, 2011, Alexandre Oliva <aol...@redhat.com> wrote:
>> According to http://gcc.gnu.org/ml/gcc-patches/2009-11/msg01082.html
>> on Nov 20, 2009, Alexandre Oliva <aol...@redhat.com> wrote:
>>> On Nov 19, 2009, Richard Guenther <richard.guent...@gmail.com> wrote:
>>>> In fact this exchanging of the LHS (or rather invalidating of the
>>>> SSA name value) should be a helper function that knows
>>>> the implementation details and avoids going through releasing
>>>> and allocating the name.
>>> Okie dokie, here's a sequence of patches that implements helper
>>> functions for this sort of stuff.
>>> The first patch introduces machinery to propagate “dying” DEFs into
>>> debug stmts, while replacing them with other SSA_NAMEs.
>> This is already in.
>>> The second extends it so as to enable the old LHS to be redefined
>>> e.g. in terms of the new LHS.  IIRC this may be useful in some other
>>> transformations that, in the process of introducing VTA, I changed from
>>> modifying stmts in place to inserting new stmts and removing others.  I
>>> haven't looked for them yet.
>>> The third uses this new feature for the case at hand, while avoiding
>>> computing the reciprocal expression if we know it won't be used.
>> Updated versions of these follow.  Regstrapped on x86_64-linux-gnu and
>> i686-linux-gnu.  Ok to install?
> I was asked to submit these again in stage1, so...  Ping?
> (updated and re-tested)

+  /* If the conditions in which this function uses VALUE change,
+     adjust gimple_replace_lhs_wants_value().  */
+  gcc_assert (gimple_replace_lhs_wants_value ()
+             == MAY_HAVE_DEBUG_STMTS);

that looks ... odd.  But I see you want to conditionally compute value.

+static inline bool
+gimple_replace_lhs_wants_value (void)

but should this not depend on the old stmt / lhs?  For example do we really
want to do this for artificial variables?  I suppose not.


> --
> Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- http://FSFLA.org/   FSF Latin America board member
> Free Software Evangelist      Red Hat Brazil Compiler Engineer

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