Changeset: 969563673a16 for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/969563673a16
Modified Files:
monetdb5/optimizer/opt_reorder.c
Branch: default
Log Message:
Add comments
diffs (51 lines):
diff --git a/monetdb5/optimizer/opt_reorder.c b/monetdb5/optimizer/opt_reorder.c
--- a/monetdb5/optimizer/opt_reorder.c
+++ b/monetdb5/optimizer/opt_reorder.c
@@ -52,6 +52,9 @@
* Also check for barrier blocks. We only allow reordering
* for a linear plan. Future extensions could consider
* re-ordering basic blocks only.
+ *
+ * For this purpose this optimizer should be run before
+ * the dataflow optimizer, because it adds barriers.
*/
typedef struct{
int cnt;
@@ -88,6 +91,11 @@ OPTdependencies(Client cntxt, MalBlkPtr
return NULL;
}
+/* Instead of malloced structures for each instruction,
+ * we can also consider a simple scan to determinee the max size
+ * and allocate a single block
+ */
+
for ( i=0; i< mb->stop; i++){
p= getInstrPtr(mb,i);
block |= p->barrier != 0;
@@ -98,11 +106,15 @@ OPTdependencies(Client cntxt, MalBlkPtr
return 0;
}
list[i]->cnt = p->argc;
+ /* Collect the dependencies of arguments on previous
instructions */
for( j=p->retc; j<p->argc; j++) {
list[i]->stmt[j] = var[getArg(p,j)];
list[var[getArg(p,j)]]->used++;
}
- /* keep the assignment order */
+ /* keep the assignment order
+ * Duplicate assignment of a variable is not wanted
+ * but can not be avoided when loops are involved
+ * In this case we bail out*/
for( j= 0; j < p->retc; j++) {
if ( var[ getArg(p,j)] ) {
//list[i]->stmt[j] = var [getArg(p,j)];
@@ -112,7 +124,7 @@ OPTdependencies(Client cntxt, MalBlkPtr
return 0;
}
}
- /* remember the last assignment */
+ /* remember the statement where a variable was last assignment
*/
for( j=0; j<p->retc; j++)
var[getArg(p,j)] = i;
}
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