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Re: [gimple-classes, committed 4/6] tree-ssa-tail-merge.c: Use gassign


On Tue, Nov 18, 2014 at 2:59 AM, David Malcolm <dmalcolm@redhat.com> wrote:
> On Mon, 2014-11-17 at 11:06 +0100, Richard Biener wrote:
>> On Sat, Nov 15, 2014 at 12:00 PM, David Malcolm <dmalcolm@redhat.com> wrote:
>> > On Thu, 2014-11-13 at 11:45 +0100, Richard Biener wrote:
>> >> On Thu, Nov 13, 2014 at 2:41 AM, David Malcolm <dmalcolm@redhat.com> wrote:
>> >> > On Tue, 2014-11-11 at 11:43 +0100, Richard Biener wrote:
>> >> >> On Tue, Nov 11, 2014 at 8:26 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>> >> >> > On Mon, Nov 10, 2014 at 05:27:50PM -0500, David Malcolm wrote:
>> >> >> >> On Sat, 2014-11-08 at 14:56 +0100, Jakub Jelinek wrote:
>> >> >> >> > On Sat, Nov 08, 2014 at 01:07:28PM +0100, Richard Biener wrote:
>> >> >> >> > > To be constructive here - the above case is from within a
>> >> >> >> > > GIMPLE_ASSIGN case label
>> >> >> >> > > and thus I'd have expected
>> >> >> >> > >
>> >> >> >> > >     case GIMPLE_ASSIGN:
>> >> >> >> > >       {
>> >> >> >> > >         gassign *a1 = as_a <gassign *> (s1);
>> >> >> >> > >         gassign *a2 = as_a <gassign *> (s2);
>> >> >> >> > >       lhs1 = gimple_assign_lhs (a1);
>> >> >> >> > >       lhs2 = gimple_assign_lhs (a2);
>> >> >> >> > >       if (TREE_CODE (lhs1) != SSA_NAME
>> >> >> >> > >           && TREE_CODE (lhs2) != SSA_NAME)
>> >> >> >> > >         return (operand_equal_p (lhs1, lhs2, 0)
>> >> >> >> > >                 && gimple_operand_equal_value_p (gimple_assign_rhs1 (a1),
>> >> >> >> > >                                                  gimple_assign_rhs1 (a2)));
>> >> >> >> > >       else if (TREE_CODE (lhs1) == SSA_NAME
>> >> >> >> > >                && TREE_CODE (lhs2) == SSA_NAME)
>> >> >> >> > >         return vn_valueize (lhs1) == vn_valueize (lhs2);
>> >> >> >> > >       return false;
>> >> >> >> > >       }
>> >> >> >> > >
>> >> >> >> > > instead.  That's the kind of changes I have expected and have approved of.
>> >> >> >> >
>> >> >> >> > But even that looks like just adding extra work for all developers, with no
>> >> >> >> > gain.  You only have to add extra code and extra temporaries, in switches
>> >> >> >> > typically also have to add {} because of the temporaries and thus extra
>> >> >> >> > indentation level, and it doesn't simplify anything in the code.
>> >> >> >>
>> >> >> >> The branch attempts to use the C++ typesystem to capture information
>> >> >> >> about the kinds of gimple statement we expect, both:
>> >> >> >>   (A) so that the compiler can detect type errors, and
>> >> >> >>   (B) as a comprehension aid to the human reader of the code
>> >> >> >>
>> >> >> >> The ideal here is when function params and struct field can be
>> >> >> >> strengthened from "gimple" to a subclass ptr.  This captures the
>> >> >> >> knowledge that every use of a function or within a struct has a given
>> >> >> >> gimple code.
>> >> >> >
>> >> >> > I just don't like all the as_a/is_a stuff enforced everywhere,
>> >> >> > it means more typing, more temporaries, more indentation.
>> >> >> > So, as I view it, instead of the checks being done cheaply (yes, I think
>> >> >> > the gimple checking as we have right now is very cheap) under the
>> >> >> > hood by the accessors (gimple_assign_{lhs,rhs1} etc.), those changes
>> >> >> > put the burden on the developers, who has to check that manually through
>> >> >> > the as_a/is_a stuff everywhere, more typing and uglier syntax.
>> >> >> > I just don't see that as a step forward, instead a huge step backwards.
>> >> >> > But perhaps I'm alone with this.
>> >> >> > Can you e.g. compare the size of - lines in your patchset combined, and
>> >> >> > size of + lines in your patchset?  As in, if your changes lead to less
>> >> >> > typing or more.
>> >> >>
>> >> >> I see two ways out here.  One is to add overloads to all the functions
>> >> >> taking the special types like
>> >> >>
>> >> >> tree
>> >> >> gimple_assign_rhs1 (gimple *);
>> >> >>
>> >> >> or simply add
>> >> >>
>> >> >> gassign *operator ()(gimple *g) { return as_a <gassign *> (g); }
>> >> >>
>> >> >> into a gimple-compat.h header which you include in places that
>> >> >> are not converted "nicely".
>> >> >
>> >> > Thanks for the suggestions.
>> >> >
>> >> > Am I missing something, or is the gimple-compat.h idea above not valid C
>> >> > ++?
>> >> >
>> >> > Note that "gimple" is still a typedef to
>> >> >   gimple_statement_base *
>> >> > (as noted before, the gimple -> gimple * change would break everyone
>> >> > else's patches, so we talked about that as a followup patch for early
>> >> > stage3).
>> >> >
>> >> > Given that, if I try to create an "operator ()" outside of a class, I
>> >> > get this error:
>> >> >
>> >> > âgassign* operator()(gimple)â must be a nonstatic member function
>> >> >
>> >> > which is emitted from cp/decl.c's grok_op_properties:
>> >> >       /* An operator function must either be a non-static member function
>> >> >          or have at least one parameter of a class, a reference to a class,
>> >> >          an enumeration, or a reference to an enumeration.  13.4.0.6 */
>> >> >
>> >> > I tried making it a member function of gimple_statement_base, but that
>> >> > doesn't work either: we want a conversion
>> >> >   from a gimple_statement_base * to a gassign *, not
>> >> >   from a gimple_statement_base   to a gassign *.
>> >> >
>> >> > Is there some syntactic trick here that I'm missing?  Sorry if I'm being
>> >> > dumb (I can imagine there's a way of doing it by making "gimple" become
>> >> > some kind of wrapped ptr class, but that way lies madness, surely).
>> >>
>> >> Hmm.
>> >>
>> >> struct assign;
>> >> struct base {
>> >>   operator assign *() const { return (assign *)this; }
>> >> };
>> >> struct assign : base {
>> >> };
>> >>
>> >> void foo (assign *);
>> >> void bar (base *b)
>> >> {
>> >>   foo (b);
>> >> }
>> >>
>> >> doesn't work, but
>> >>
>> >> void bar (base &b)
>> >> {
>> >>   foo (b);
>> >> }
>> >>
>> >> does.  Indeed C++ doesn't seem to provide what is necessary
>> >> for the compat trick :(
>> >>
>> >> So the gimple-compat.h header would need to provide
>> >> additional overloads for the affected functions like
>> >>
>> >> inline tree
>> >> gimple_assign_rhs1 (gimple *g)
>> >> {
>> >>   return gimple_assign_rhs1 (as_a <gassign *> (g));
>> >> }
>> >>
>> >> that would work for me as well.
>> >>
>> >> >> Both avoid manually making the compiler happy (which the
>> >> >> explicit as_a<> stuff is!  It doesn't add any "checking" - it's
>> >> >> just placing the as_a<> at the callers and thus make the
>> >> >> runtine ICE fire there).
>> >> >>
>> >> >> As much as I don't like "global" conversion operators I don't
>> >> >> like adding overloads to all of the accessor functions even more.
>> >> >
>> >> > (nods)
>> >> >
>> >> > Some other options:
>> >> >
>> >> > Option 3: only convert the "easy" accessors: the ones I already did in
>> >> > the /89 patch kit, as reviewed by Jeff, and rebased by me recently,
>> >> > which is this 92-patch kit:
>> >> >   "[gimple-classes, committed 00/92] Initial slew of commits":
>> >> >      https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02791.html
>> >> > Doing so converts about half of the gimple_foo_ accessors to taking a
>> >> > gfoo *, giving a mixture of GIMPLE_CHECK vs subclass use.   I believe
>> >> > the quality of those patches was higher than the later ones on the
>> >> > branch: I was doing the places that didn't require the invasive/verbose
>> >> > changes seen in the later patches.  Shelve the remaining ~80
>> >> > increasingly ugly patches, starting a new branch to contain just the
>> >> > good ones.
>> >
>> > I've created a branch "dmalcolm/gimple-classes-v2-option-3"
>> > https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/gimple-classes-v2-option-3
>> >
>> > which takes the work reviewed by Jeff and the most trivial of the merger
>> > followup work, throwing away the ~80 unloved followup patches on
>> > dmalcolm/gimple-classes.
>> >
>> > I've merged from yesterday's trunk r217593 into that new branch,
>> > resolving conflicts.
>> >
>> > I did this in two parts: the basic merger as
>> >   bd7fe714158f0c600caa05be7d744fd9139b8afb
>> > resolving conflicts, with a followup patch to fixup new code from trunk
>> > that used accessors that on the branch required a gimple subclass.
>> >
>> > Attached is that 2nd part of the merger.
>> >
>> > Successfully bootstrapped and regrtested on x86_64-unknown-linux-gnu;
>> > same regrtest results as a control bootstrap of trunk's r217593.
>> >
>> > I appreciate Jakub and others have concerns about the overall approach.
>> > I'm not sure which of option 2 (gimple-compat.h), option 3 (this one),
>> > option 4 (just convert fields and non-accessor params), or defer to gcc
>> > 6 is the best one, but I'm sleep-deprived and wanted to submit this
>> > before the stage1 deadline.
>> >
>> > The other commits on this pruned branch that haven't been reviewed yet
>> > are:
>> >
>> > [gimple-classes, committed 88/92] Preparatory work before subclass
>> > renaming
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02820.html
>>
>> Ok.
>>
>> > [gimple-classes, committed 89/92] Eliminate subclass typedefs from
>> > coretypes.h
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02838.html
>>
>> Ok.
>>
>> > [gimple-classes, committed 90/92] Automated renaming of gimple
>> > subclasses
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02828.html
>>
>> Ok.
>>
>> > [gimple-classes, committed 91/92] Remove out-of-date references to
>> > typedefs]
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02874.html
>>
>> Ok.
>>
>> > [gimple-classes, committed 92/92] Update gimple.texi class hierarchy
>> > diagram
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02818.html
>>
>> Ok.
>>
>> > [gimple-classes] Merge trunk r216157-r216746 into branch
>> >   https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02982.html
>>
>> Ok.
>
> Thanks.  You said "Ok" to the various patches I pinged, but I don't
> think you commented on the patch that was attached to the email.
>
> Is that one OK?  It's:
>  https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01935.html
> in the archives.

Yes, that one is ok as well.

> I believe that's the only unreviewed patch on the branch
> "dmalcolm/gimple-classes-v2-option-3":
> https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/gimple-classes-v2-option-3
>
> Assuming that's OK, I want to merge that branch to trunk in the next day
> or so.

Fine with me.

>> > Also, presumably if this were merged, it would require a followup with
>> > the gimple to gimple * fixup you wanted? (which we talked about doing as
>> > an early stage3 thing IIRC [1]).
>>
>> Yeah, that would be nice (to remind people - this is about getting rid
>> of const_gimple and thus avoids introducing tons of new const_
>> for all the subclasses).
>
> FWIW I got rid of all of those typedefs in the patches above (89/92 in
> particular); the subclasses on the branch are already using explicit
> ptrs, so it's more about consistency between base class ptrs and
> subclass ptrs, to avoid:
>
>   gimple  stmt;
>   gphi   *phi;
>   gcall  *call_stmt;
>
> in favor of:
>   gimple *stmt;  /* <-- note this one */
>   gphi   *phi;
>   gcall  *call_stmt;

right.

> I'd already done that for the subclasses on the branch, and the diff
> between the branch and trunk is relatively sane.
>
> By contrast, doing the gimple -> gimple * fixup will generate a huge
> diff, so that's something to do after merging the branch.
> I'll post the patch here later this week (or a link to it, it's likely
> to be too big even compressed for the ML).

Thanks,
Richard.

> Dave
>
>> Thanks,
>> Richard.
>>
>> > Thanks
>> > Dave
>> > [1] e.g. https://gcc.gnu.org/ml/gcc-patches/2014-10/msg01536.html
>> >
>> >
>> >> > Option 4: don't convert any accessors, but instead focus on fields of
>> >> > structs (e.g. "call_stmt" within a cgraph_edge), and on params of other
>> >> > functions (e.g. phi-manipulation code).  That way we'd avoid the
>> >> > inconsistency of some accessors using GIMPLE_CHECK and some using
>> >> > subclasses - all would continue to consistently use GIMPLE_CHECK, but
>> >> > there would be some extra type-checking and self-documentation of the
>> >> > expected statement kinds in the code.
>> >> >
>> >> >
>> >> >
>> >> > FWIW, option 3 is my preferred approach (I've already done the bulk of
>> >> > the work and it's already been reviewed; it would need an update merger
>> >> > from trunk, and there's the big gimple to gimple * fixup you wanted).
>> >>
>> >> Works for me as well.  The compat solution looks somewhat appealing
>> >> as we can then incrementally fix up things rather than requiring to
>> >> mass-convert everything.
>> >>
>> >> Thanks,
>> >> Richard.
>> >>
>> >> >> Whether you enable them generally or just for selected files
>> >> >> via a gimple-compat.h will be up to you (but I'd rather get
>> >> >> rid of them at some point).
>> >> >>
>> >> >> Note this allows seamless transform of "random" functions
>> >> >> taking a gimple now but really only expecting a single kind.
>> >> >>
>> >> >> Note that we don't absolutely have to rush this all in for GCC 5.
>> >> >> Being the very first for GCC 6 stage1 is another possibility.
>> >> >> We just should get it right.
>> >> >
>> >> > Thanks
>> >> > Dave
>> >> >
>> >
>
>


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