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

[Ryotaro Kasuga via llvm-commits]

================
@@ -80,6 +80,17 @@ static void warnAboutLeftoverTransformations(Loop *L,
            "requested transformation; the transformation might be disabled or "
            "specified as part of an unsupported transformation ordering");
   }
+
+  if (hasInterchangeTransformation(L) == TM_ForcedByUser) {
+    LLVM_DEBUG(dbgs() << "Leftover interchange transformation\n");
+    ORE->emit(
+        DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
+                                          "FailedRequestedInterchange",
+                                          L->getStartLoc(), L->getHeader())
+        << "loop not interchanged: the optimizer was unable to perform the "
+           "requested transformation; the transformation might be disabled or "
+           "specified as part of an unsupported transformation ordering");
+  }
----------------
kasuga-fj wrote:

> Consider adding the loop interchange metadata to https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/Scalar/WarnMissedTransforms.cpp, such that for whatever reason there is still interchange instructions on some loops, the user gets a warning.

Is this what you intended?

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