[Bug middle-end/28071] [4.1 regression] A file that can not be compiled in reasonable time/space

["mkuvyrkov at ispras dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #57 from mkuvyrkov at ispras dot ru  2007-01-15 07:52 -------
Subject: Re:  [4.1 regression] A file that can not be
 compiled in reasonable time/space

Thanks!  Very useful comments.  I'm continuing to work on cleaning the 
patch (especially on writing the comments) and making code more 
transparent.  Below are my comments on yours:

zaks at il dot ibm dot com wrote:
> ------- Comment #56 from zaks at il dot ibm dot com  2007-01-15 07:19 -------
> (In reply to comment #55)
>> Created an attachment (id=12879)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12879&action=view)
>  --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12879&action=view) [edit]
>> Patch for scheduler dependency lists.
> 
> Looks like a pretty good cleanup IMHO. Here are some comments.
> 
> o dep_def: representing a dependence edge including both producer and consumer
> is very handy, albeit somewhat redundant as we're usually traversing all cons
> connected to a pro or vice versa.
This allows us to keep all things in one place - one of the things 
current deps don't provide.  I.e., when changing some property of the 
dep we need to find a corresponding to that dep nodes in both backward 
and forward lists and apply the change to two places instead of one.

  (I.e., has its pros and cons, but mostly pros
> I agree - also done in ddg.h/ddg_edge.) Maybe comment why both 'kind' and 'ds'
> are needed, as one supersedes the other.
There will be.  Thanks.

> 
> o dep_node_def: this is a node in a (doubly-linked) chain, but it represents an
> *edge* in terms of the data-dependence graph. The prev_nextp field is a "/*
Right!  I struggled to figure out the correct name and didn't prevail. 
Thanks for the tip.  It'll be dep_edge.

> Pointer to the next field of the previous node in the list.  */" except for the
> first node on the list, whose prev_nextp points to itself, right?
No.  Prev_nextp field of the first node points to deps_list->first. 
This allows us not to distinguish first node from the others.  I'll fix 
the comment.

> 
> o dep_data_node_def: holding the two conjugate dependence edges together is
> very useful when switching directions. But perhaps most of the accesses go in
> one direction (e.g. iterating over cons of a pro), and having both conjugates
> structed together may reduce cache efficiency. So you may consider connecting
> each dep_node_def to its conjugate, not necessarily forcing them to be placed
> adjacent in memory.
Dep_def and both edges were placed in one structure so that they could 
be allocated and freed within a single alloc/free.  As I understand you 
propose putting two pointers inside dep_edge_def: one to the dep_def and 
one to the opposite edge.  Currently we have one pointer in dep_edge_def 
to the dep_data_node which have all that pointers.  And probably I'm 
missing something, but I don't see how your way can improve cache 
efficiency.

> 
> o To add to the checking routines, the following can be checked: every
> dep_node_def is pointed-to by either its data->back xor its data->forw, right?
> If so, this can be used to identify if a dep_node_def is forward or backward;
> that all nodes on a list are forward (and share the same pro) or backward (and
> share the same con); and to assert the following regarding L:
> +/* Add a dependency described by DEP to the list L.
> +   L should be either INSN_DEPS1 or RESOLVED_DEPS1.  */
Good idea.

> 
> o insn_cost (insn, dep): maybe it's better to break this into insn_cost (insn)
> of a producer regardless of consumers, and "dep_cost (dep)".
Agree.

> 
> o The comment explaining what 'resolve_dep' does can be inlined together with
> its code. 
Agree.

> 
> +/* Detach dep_node N from the list.  */
> +static void
> +dep_node_detach (dep_node_t n)
> +{
> +  dep_node_t *prev_nextp = DEP_NODE_PREV_NEXTP (n);
> +  dep_node_t next = DEP_NODE_NEXT (n);
> +
> +  *prev_nextp = next;
> +
> +  if (next != NULL)
> +    DEP_NODE_PREV_NEXTP (next) = prev_nextp;
> maybe complete the detachment by adding:
> DEP_NODE_PREV_NEXTP (n) = NULL;
> DEP_NODE_NEXT (n) = NULL;
Probably, you are right.

> Ayal.

Thanks,

Maxim


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28071