The assignment to the node's variable must come after any uses of that
node, which the node's parent set indicates. In the swap test, this was
not a problem as the node had no parents, and in the link order test, it
just happened(?) to work.
While using just the label node's reachable set was sufficient for a
simple swap (t = a; a = b; b = t;), it is not sufficient for
read-before-write dependencies such as found in linked-list building:
{ o = array[ind]; o.next = obj; obj = o; }
The assignment to o.next uses obj, but that use is hidden because obj's
reachable nodes does not include o thus assigning o to obj causes the
array dereference to be assigned directly to obj and thus o.next winds
up pointing to o instead of whatever obj was. The parent nodes of obj's
node are its users, so any new assigned to obj must come after those
parents as well as any node reachable by obj's node.
Fixes a runaway loop error when adding a frikbot to the server.
When moving an identifier label from one node to another, the first node
must be evaluated before the second node, which the edge guarantees.
However, code for swapping two variables
t = a; a = b; b = t;
creates a dependency cycle. The solution is to create a new leaf node
for the source operand of the assignment. This fixes the swap.r test
without pessimizing postop code.
This takes care of the core problem in #3, but there is still room for
improvement in that the load/store can be combined into a move.
This reverts commit 2fcda44ab0.
Killing the node is not the correcgt answer as it blocks many
optimization opportunities. The correct answer is adding edges to
describe the temporal dependencies. Of course, this breaks the swap.r
test.
In order to correctly handle swap-style code
{ t = a; a = b; b = t; }
edges need to be created for each of the assignments moving an
identifier lable, but the dag must remain acyclic (the above example
wants to create a cycle). Having the reachable nodes recorded makes
checking for potential loops a quick operation.
Identifiers can be constants. I don't remember quite what it fixed other
than some bogus kill relations in the dags (which might have caused
issues later).
There's still some cleanup to do, but everything seems to be working
nicely: `make -j` works, `make distcheck` passes. There is probably
plenty of bitrot in the package directories (RPM, debian), though.
The vc project files have been removed since those versions are way out
of date and quakeforge is pretty much dependent on gcc now anyway.
Most of the old Makefile.am files are now Makemodule.am. This should
allow for new Makefile.am files that allow local building (to be added
on an as-needed bases). The current remaining Makefile.am files are for
standalone sub-projects.a
The installable bins are currently built in the top-level build
directory. This may change if the clutter gets to be too much.
While this does make a noticeable difference in build times, the main
reason for the switch was to take care of the growing dependency issues:
now it's possible to build tools for code generation (eg, using qfcc and
ruamoko programs for code-gen).
Killed nodes can leave stray (dangling) edges that cause some confusion
in the dot graphs and may cause problems later on down the track, so
ensure there are no dangling edges.
The reason double-alias fails is when the double assignment occurs, the
int operands don't yet have leaf nodes and thus the nodes cannot be
killed. This doesn't fix the bug.
Rather than prefixing free_ to the supplied name, suffix _freelist to the
supplied name. The biggest advantage of this is it allows the free-list to
be a structure member. It also cleans up the name-space a little.
Dead nodes are those that generate unused values (unassigned leaf nodes,
expressions or destinationless move(p) nodes). The revoval is done by the
flow analysis code (via the dags code) so that any pre and post removal
flow analysis and manipulation may be done (eg, available expressions).
This fixes the segfault/null pointer access in sendv.r. While I wanted to
use the edge setting code to set the live bit, I didn't expect it to be
this easy. def_visit_all is proving to be worth every bit it consumes :)
