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Be slightly picky about which nodes to kill.

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Constant/label nodes should never be killed because they can (in theory)
never change. While constants /can/ change in the Quake VM, it's not worth
worrying about as there would be much more important things to worry about
(like 2+2 not giving 4).

Due to the hoops one would have to jump through, it is assumed that a
pointer or an offset from that pointer will never overwrite the pointer.
This commit is contained in:
Bill Currie 2012-11-20 15:28:57 +09:00
parent 22d72f33d2
commit 87121b4cf1
1 changed files with 18 additions and 2 deletions
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20
tools/qfcc/source/dags.c
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@ -388,9 +388,25 @@ static void
dag_kill_nodes (dag_t *dag, dagnode_t *n)
{
int i;
dagnode_t *node;
for (i = 0; i < dag->num_nodes; i++)
dag->nodes[i]->killed = 1;
for (i = 0; i < dag->num_nodes; i++) {
node = dag->nodes[i];
if (node == n->children[1]) {
// assume the pointer does not point to itself. This should be
// reasonable because without casting, only a void pointer can
// point to itself (the required type is recursive).
continue;
}
if (node->label->op && !op_is_identifier (node->label->op)) {
// While constants in the Quake VM can be changed via a pointer,
// doing so would cause much more fun than a simple
// mis-optimization would, so consider them safe from pointer
// operations.
continue;
}
node->killed = 1;
}
n->killed = 0;
}