[llvm] [LV] Add tests for excluded cases in epiloge tail-folding (PR #217364)

[David Sherwood via llvm-commits]

================
@@ -7223,23 +7225,64 @@ getEpilogueTailLowering(const LoopVectorizationCostModel &MainCM, const Loop *L,
   if (!EnableEpilogueVectorization) {
     reportVectorizationInfo(
         "Options conflict, epilogue vectorization is disallowed while "
-        "epilogue tail-folding allowed!\n",
+        "epilogue tail-folding allowed!",
         "UnsupportedEpilogueTailFoldingPolicy", ORE, L);
     return CM_EpilogueAllowed;
   }
 
+  if (!Hints.getWidth() || !hasForcedEpilogueVF()) {
+    reportVectorizationInfo("For now, Epilogue tail-folding can't be "
+                            "applied without forced main/epilogue loop VF",
+                            "UnsupportedEpilogueTailFoldingPolicy", ORE, L);
+    return CM_EpilogueAllowed;
+  }
+
+  if (!L->isInnermost()) {
+    reportVectorizationInfo(
+        "Epilogue tail-folding is not supported for outer loop",
+        "InvalidTailFoldedEpilogue", ORE, L);
+    return CM_EpilogueAllowed;
+  }
+
   // If scalar epilogue is explicitly required, we can't apply TF.
   if (MainCM.requiresScalarEpilogue(/*IsVectorizing*/ true)) {
-    LLVM_DEBUG(dbgs() << "LV: Epilogue tail-folding can't be applied because "
-                         "scalar epilogue is required\n"
-                         "LV: Fall back to a normal epilogue\n");
+    reportVectorizationInfo(
+        "Epilogue tail-folding can't be applied because scalar epilogue is "
+        "required. Fall back to a normal epilogue",
+        "InvalidTailFoldedEpilogue", ORE, L);
     return CM_EpilogueAllowed;
   }
 
   // If having epilogue is NOT allowed, then no epilogue to apply TF for.
   if (!MainCM.isEpilogueAllowed()) {
-    LLVM_DEBUG(dbgs() << "LV: No epilogue to apply tail-folding for.\n"
-                         "LV: Fall back to a normal epilogue\n");
+    reportVectorizationInfo("No epilogue to apply tail-folding for. Fall back "
+                            "to a normal epilogue",
+                            "InvalidTailFoldedEpilogue", ORE, L);
+    return CM_EpilogueAllowed;
+  }
+
+  // For now epilogue TF is not supported for some kinds of reductions that
+  // results in more overhead
----------------
david-arm wrote:

Are you saying that when forcing tail-folded epilogues the resulting code is functionally correct, but just not optimal? If so, then I'm a bit worried that with this change we'll have no way to actually test the feature even when forced.
Perhaps it's fine to permit forcing it for now, then when you start working on the cost model we can disable it unless forced explictly?

https://github.com/llvm/llvm-project/pull/217364