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) [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
