PING: Fwd: Re: [patch] new API for value_range

[Aldy Hernandez]

-------- Forwarded Message --------
Subject: Re: [patch] new API for value_range
Date: Thu, 11 Oct 2018 14:25:43 -0400
From: Aldy Hernandez <aldyh@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>
CC: GCC Patches <gcc-patches@gcc.gnu.org>, Andrew MacLeod 
<amacleod@redhat.com>



On 10/11/18 5:47 AM, Richard Biener wrote:
> On Thu, Oct 11, 2018 at 10:19 AM Aldy Hernandez <aldyh@redhat.com> wrote:
>>
>> Hi Richard.  Thanks for reviewing.
>>
>> On 10/10/18 6:27 AM, Richard Biener wrote:
>>> On Tue, Oct 9, 2018 at 6:23 PM Aldy Hernandez <aldyh@redhat.com> wrote:
>>>>
>>>> I'm assuming the silence on the RFC means nobody is viscerally opposed
>>>> to it, so here goes the actual implementation ;-).
>>>>
>>>>           FWI: https://gcc.gnu.org/ml/gcc-patches/2018-10/msg00157.html
>>>>
>>>> My aim is no change to the current functionality, but there are some
>>>> things that changed slightly (with no appreciable change in
>>>> bootstrapability or tests).
>>>>
>>>> 1.  Primarily, we were building value_ranges by modifying them in-flight
>>>> with no regards to the validity of the resulting range.  By enforcing
>>>> the API, I noticed we periodically built VR_VARYING / VR_UNDEFINED, but
>>>> left the equivalence bits uncleared.  This comment in the original
>>>> header file indicates that this is invalid behavior:
>>>>
>>>>      /* Set of SSA names whose value ranges are equivalent to this one.
>>>>         This set is only valid when TYPE is VR_RANGE or VR_ANTI_RANGE.  */
>>>>
>>>> The API now enforces this upon construction.
>>>>
>>>> 2. I also saw us setting min/max when VARYING or UNDEFINED was set.
>>>> This is invalid.  Although these values were being ignored, the API now
>>>> enforces this.
>>>>
>>>> 3. I saw one case in set_value_range_with_overflow() were we were
>>>> building an invalid range with swapped ranges, where we were silently
>>>> depending on somebody further up the call chain to swap them for us.
>>>> I've fixed this at creation.
>>>>
>>>> 4. There is one assert in ipcp_vr_lattice which I hope to remove, but
>>>> left as proof that the original VR_UNDEFINED set was not necessary, as
>>>> it is now done by default on an empty constructor:
>>>>
>>>> -  void init () { m_vr.type = VR_UNDEFINED; }
>>>> +  void init () { gcc_assert (m_vr.undefined_p ()); }
>>>>
>>>> One last note.  The file tree-vrp.c already has a cripple API of sorts
>>>> in the form of functions (set_value_range_to_varying, etc).  I have
>>>> tried to keep those functions available, by calling the API under the
>>>> covers, but would be okay in removing them altogether as a follow-up.
>>>>
>>>> Please refer to the RFC wrt the min/max/vrtype accessors, as well as the
>>>> new tree type field.
>>>>
>>>> I am quoting the class declaration below to make it easy to review at a
>>>> high level.
>>>>
>>>> Tested on x86-64 Linux.  All languages, including Ada and Go.
>>>>
>>>> OK for trunk?
>>>
>>> Reviewing in patch order.
>>>
>>>> Aldy
>>>>
>>>> class GTY((for_user)) value_range
>>>> {
>>>>     public:
>>>>      value_range ();
>>>>      value_range (tree type);
>>>>      value_range (value_range_type, tree type, tree, tree, bitmap = NULL);
>>>>      bool operator== (const value_range &) const;
>>>>      bool operator!= (const value_range &) const;
>>>>      void intersect (const value_range *);
>>>>      void union_ (const value_range *);
>>>
>>> with trailing underscore?  seriously?
>>
>> Hey!  You complained about Union() last year, at which point the
>> consensus was that trailing underscores would be ok for symbol names
>> that clashed with keywords.
> 
> ;)
> 
> I also thought about union_into / union_with.  As opposed to a hypothetical
> 
>    value_range union (const value_range& a, const value_range& b)
> 
> function.
> 
>> And yes, it was also discussed whether we should overload | and ^ for
>> union and intersection, but was denied for readability and what have yous.
>>
>>>
>>>>      /* Like operator== but ignore equivalence bitmap.  */
>>>>      bool ignore_equivs_equal_p (const value_range &) const;
>>>>      /* Like a operator= but update equivalence bitmap efficiently.  */
>>>>      void copy_with_equiv_update (const value_range *);
>>>>
>>>>      /* Types of value ranges.  */
>>>>      bool undefined_p () const;
>>>>      bool varying_p () const;
>>>>      bool symbolic_p () const;
>>>>      bool numeric_p () const;
>>>>      void set_undefined (tree = NULL);
>>>>      void set_varying (tree = NULL);
>>>
>>> I'd appreciate comments on those predicates, esp. as you
>>> replace positive tests by negative ones like in
>>
>> Done.
>>
>>>
>>>      /* If we found any usable VR, set the VR to ssa_name and create a
>>>         PUSH old value in the stack with the old VR.  */
>>> -  if (vr.type == VR_RANGE || vr.type == VR_ANTI_RANGE)
>>> +  if (!vr.undefined_p () && !vr.varying_p ())
>>>        {
>>>
>>> I'd also spell numeric_p as constant_p or drop it alltogether
>>> since !symbolic_p should imply it given varying_p and undefined_p
>>> are just some special-cases of "numeric_p" (full and empty range).
>>
>> Done.
>>
>>>
>>> That said, for the time being I'd use non_symbolic_range_or_anti_range_p
>>> instead of numeric_p () (seeing that you maybe want to hide the fact
>>> that we have anti-ranges?)
>>
>> Errr... No.
>>
>>>
>>> -  value_range vr = VR_INITIALIZER;
>>> +  value_range vr (TREE_TYPE (name));
>>>
>>> so you basically forgo with the fact that empty ranges are universal?
>>> I don't like it too much that we have to invent a type here.  Why enforce this
>>> and not allow/force type == NULL_TREE for empty ranges?
>>>
>>> One could argue VARYING is also universal to some extent and useful
>>> only with context, so similar argument applies to your change forcing
>>> a type for set_value_range_to_varying.
>>>
>>> -      value_range vr = VR_INITIALIZER;
>>> +      value_range vr;
>>>
>>> oh, so you do have a default constructor.
>>>
>>>>
>>>>      /* Equivalence bitmap methods.  */
>>>>      bitmap equiv () const;
>>>>      void set_equiv (bitmap);
>>>
>>> Err, I think we've settled on _not_ wrapping all member accesses
>>> with get/set methods, didn't we?  I personally dislike that very much.
>>>
>>>>      void equiv_free ();
>>>>      void equiv_copy (const value_range *);
>>>>      void equiv_clear ();
>>>>      void equiv_and (const value_range *);
>>>>      void equiv_ior (const value_range *);
>>>
>>> Likewise I find this useless abstraction.  It's even questionable
>>> if _free/_clear/_copy are good APIs here.  This should be all
>>> hidden in intersect/union which I do not find in the API at all...
>>
>> I missed that discussion.  We did?  I dislike exposing the internals.
>> Abstracting things out makes it easier to change things in the future--
>> or insert instrumenting code, or whatever.
> 
> OK, I might misremember and it's eventually just my personal taste
> against slapping a setFoo/getFoo method in a class as the first
> thing to do after adding a m_Foo member...
> 
>> That said, I have removed copy/free/and/or.  As you said, it was much
>> easier to make the details internal to the intersect/union member functions.
>>
>> However, I have kept:
>>
>>     bitmap equiv () const;
>>     void set_equiv (bitmap);
>>     void equiv_clear ();
>>
>> I think we can get away with just having a clear, instead of a free, as
>> it's all in an obstack and there doesn't seem to be any consistent use
>> of free vs. clear throughout (except one or two, which I've kept).
> 
> Yeah.
> 
>> Also, we don't really need to expose set_equiv(), but for its one use in
>> vr_values::add_equivalence().  One option could be to make vr_values and
>> value_ranges friends and let add_equivalence touch m_equiv.  But that's
>> a bit heavy handed.
>>
>> Or we could add this to the API instead of set_equiv():
>>
>> void
>> value_range::add_equivalence (bitmap_obstack obstack, tree var)
>> {
>> }
>>
>> I don't know how I feel about passing the obtack, or including
>> "bitmap.h" from everywhere tree-vrp.h is used (that is, everywhere).
> 
> Equivalences are evil ;)  But I guess passing in the obstack works
> for me.  Maybe as trailing argument, defaulted to NULL in which
> case we use the default bitmap obstack?

Done.

> 
>> For equiv(), we could remove virtually all of its uses, since 99% of
>> them are in the form:
>>
>>          set_value_range (vr, VR_SOMETHING, min, max, vr->equiv ())
>>
>> Instead we could We could provide:
>>
>>          vr->update (VR_SOMETHING, min, max);
>>
>> ...which is just like set_value_range, but keeping the equivalences intact.
> 
> Yep, sounds good.

Done.

> 
>>   > hidden in intersect/union which I do not find in the API at all...
>>
>> How could you, it was front and center ;-):
>>
>>     void intersect (const value_range *);
>>     void union_ (const value_range *);
> 
> Missed that in the first review and then failed to delete that comment ;)
> 
>>>
>>>>
>>>>      /* Misc methods.  */
>>>>      tree type () const;
>>>
>>> type() and vrtype() is confusing - value_type() and range_kind() maybe?
>>
>> How about we keep type(), since 99% of all uses of "type" in the
>> compiler are "tree type", so it's easy to figure out.  And instead of
>> range_kind() we use kind().  It's already obvious it's a range, so
>> vr->kind() reads fine IMO.
> 
> Works for me.

Done.

> 
>>>
>>>>      bool null_p () const;
>>>>      bool may_contain_p (tree) const;
>>>>      tree singleton () const;
>>>
>>> No documentation? :/   Why null_p but singleton (instead of singleton_p)?
>>
>> Documented.
>>
>> Singleton returns the singleton if found, otherwise returns NULL.
>> NULL_P returns true/or false.  I thought the preferred way was for _p to
>> always return booleans.
> 
> Ah, missed that "detail"...
> 
>> I don't feel strongly, so I've renamed it to singleton_p() since a
>> NULL_TREE is as good as false.  Another option is:
>>
>>          bool singleton_p (tree *result = NULL)
>>
>> Hmmm...I like this last one.  What do you think?
> 
> Like it as well.

Done.

> 
>>>
>>>>      void set_and_canonicalize (enum value_range_type, tree, tree, tree,
>>>> bitmap);
>>>
>>> Why's that necessary if you enforce sanity?
>>
>> Canonicalize also does some optimizations like converting anti-ranges
>> into ranges if possible.  Although I would be OK with putting that
>> functionality in value_range::set() to be done on creation, I don't know
>> how I feel about polluting the creation code with fixing swapped min/max:
>>
>>     /* Wrong order for min and max, to swap them and the VR type we need
>>        to adjust them.  */
>>
>> It feels wrong to construct a range with swapped end-points, and hope
>> things turn out ok.  ISTM that canonicalize() clearly specifies intent:
>> I'm giving you a shitty range, fix it.
>>
>> Thoughts?
> 
> OK, let's keep it the way you had it.  I never liked this part very much
> (even though I added it!).

Sounds like you need to have a long talk with yourself ;-).

> 
>>>
>>>>      void dump () const;
>>>>
>>>>      /* Temporary accessors that should eventually be removed.  */
>>>>      enum value_range_type vrtype () const;
>>>>      tree min () const;
>>>>      tree max () const;
>>>>
>>>>     private:
>>>>      void set (value_range_type, tree type, tree, tree, bitmap);
>>>>      void check ();
>>>>      bool equal_p (const value_range &, bool ignore_equivs) const;
>>>>
>>>>      enum value_range_type m_vrtype;
>>>>     public:
>>>>      /* These should be private, but GTY is a piece of crap.  */
>>>>      tree m_min;
>>>>      tree m_max;
>>>>      tree m_type;
>>>
>>> m_type is redundant (see above).
>>
>> Removed.
>>
>> Tested on x86-64 Linux.
>>
>> Aldy
>>
>> p.s. Oh yeah, it wouldn't be an Aldy patch without an irrelevant bit
>> added for good measure:
>>
>> +void
>> +bitmap_head::dump ()
>> +{
>> +  debug (this);
>> +}
>>
>> I find having ->dump() available for each and every structure in GCC
>> helpful in debugging.  At some point we should standardize on dump(FILE
>> *) and debug() to dump to stderr.  But alas, there are too many dump()'s
>> that already dump to stderr :-/.
> 
> FWIW I like
> 
> void dump (const bitmap_head&);
> 
> more since it doesn't clutter the APIs and can theoretically be very
> easily not built into a release compiler.  And IIRC we already have
> global overloads of debug () for exactly the reason you cite.  Having
> both styles is IMHO not good.  (and I've stated my preference - feel
> free to provide statistics for in-tree uses ;))

Ughh, maybe in the future I'll sit down and convert everything to 
something regular.

Tested with all languages on x86-64 Linux.

OK for trunk?

Aldy

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