[llvm] [LoopInterchange] Add metadata to control loop-interchange (PR #127474)

[Ryotaro Kasuga via llvm-commits]

================
@@ -530,19 +566,30 @@ struct LoopInterchange {
                    const DenseMap<const Loop *, unsigned> &CostMap) {
     Loop *OuterLoop = LoopList[OuterLoopId];
     Loop *InnerLoop = LoopList[InnerLoopId];
+    MDNode *LoopID = OuterLoop->getLoopID();
     LLVM_DEBUG(dbgs() << "Processing InnerLoopId = " << InnerLoopId
                       << " and OuterLoopId = " << OuterLoopId << "\n");
+    std::optional<bool> OuterLoopEnabled = findMetadata(OuterLoop);
+    std::optional<bool> InnerLoopEnabled = findMetadata(InnerLoop);
+    if (OuterLoopEnabled == false || InnerLoopEnabled == false) {
+      LLVM_DEBUG(dbgs() << "Not interchanging loops. It is disabled.\n");
+      return false;
+    }
     LoopInterchangeLegality LIL(OuterLoop, InnerLoop, SE, ORE);
     if (!LIL.canInterchangeLoops(InnerLoopId, OuterLoopId, DependencyMatrix)) {
       LLVM_DEBUG(dbgs() << "Not interchanging loops. Cannot prove legality.\n");
       return false;
     }
     LLVM_DEBUG(dbgs() << "Loops are legal to interchange\n");
-    LoopInterchangeProfitability LIP(OuterLoop, InnerLoop, SE, ORE);
-    if (!LIP.isProfitable(InnerLoop, OuterLoop, InnerLoopId, OuterLoopId,
-                          DependencyMatrix, CostMap, CC)) {
-      LLVM_DEBUG(dbgs() << "Interchanging loops not profitable.\n");
-      return false;
+
+    // If the interchange is explicitly enabled, skip the profitability check.
----------------
kasuga-fj wrote:

I believe it is reasonable and have changed to skip the profitability check when the loop has metadata that explicitly specifies exchange.

https://github.com/llvm/llvm-project/pull/127474