private void tryPermute(LoopHeaderChord topLoop) {
Vector<LoopHeaderChord> loopNest = topLoop.getTightlyNestedLoops();
if (loopNest == null) return;
int loopDepth = loopNest.size();
LoopHeaderChord bottom = loopNest.get(loopDepth - 1);
if (!unsafe && !legalLoop(bottom)) return;
// Set the loop costs for the loops in a loop nest. The cost for a loop is
// the cost of executing the nest with that loop in the innermost nesting.
Table<Declaration, SubscriptExpr> arrayRefs = new Table<Declaration, SubscriptExpr>();
if (!topLoop.getSubscriptsRecursive(arrayRefs)) return;
graph = topLoop.getDDGraph(false);
if (graph == null) return;
if (trace) System.out.println(" " + graph);
int[] loopIndex = new int[loopDepth];
Cost[] loopCostList = new Cost[loopDepth];
Vector<RefGroup> refGroups = new Vector<RefGroup>(20);
for (int i = 0; i < loopDepth; i++) {
LoopHeaderChord loop = loopNest.elementAt(i);
if (trace) System.out.println(" " + i + " " + loop);
computeRefGroups(loop.getNestedLevel(), 2, 2, arrayRefs, refGroups);
Cost lc = computeRefCostSum(loop, refGroups);
if (trace) System.out.println(" " + i + " " + lc);
loopCostList[i] = lc;
loopIndex[i] = i; // the outtermost loop is at position 0
Cost tp = tripProduct(loopNest, loop);
if (trace) System.out.println(" " + i + " " + tp);
lc.multiply(tp);
if (trace) System.out.println(" " + i + " " + lc);
}
boolean permuted = sortByCost(loopCostList, loopIndex);
if (!permuted) return;
if (trace) {
System.out.print(" permute " + loopDepth);
System.out.print(":");
for (int i = 0; i < loopIndex.length; i++) System.out.print(" " + loopIndex[i]);
System.out.println("");
}
int[][] ddVec = getDDVec(arrayRefs, loopDepth);
if (trace) printDDInfo(ddVec, loopDepth);
if (!isLegal(loopIndex, ddVec)) return;
if (trace) System.out.println(" permute " + loopDepth);
int[] rank = new int[loopDepth];
// We will do sorting on the rank vector, which corresponds to the interchange we need.
for (int i = 0; i < loopDepth; i++) {
int loopNum = loopIndex[i];
rank[loopNum] = i;
}
if (trace) printOrder(rank);
boolean changed = true;
while (changed) {
changed = false;
for (int i = 0; i < loopDepth - 1; i++) {
int j = i + 1;
int outerRank = rank[i];
int innerRank = rank[j];
if (innerRank >= outerRank) continue;
LoopHeaderChord innerLoop = loopNest.elementAt(j);
LoopHeaderChord outerLoop = loopNest.elementAt(i);
if (!outerLoop.isDDComplete() || outerLoop.inhibitLoopPermute()) continue;
if (!innerLoop.isDDComplete() || innerLoop.inhibitLoopPermute()) continue;
changed = true;
rank[i] = innerRank;
rank[j] = outerRank;
loopNest.setElementAt(innerLoop, i);
loopNest.setElementAt(outerLoop, j);
performLoopInterchange(innerLoop, outerLoop);
}
}
}
