[mlir][affine] Vectorizer test notifies the case with the unparallel loop with reduction

Vectorizer test does not support unparallel loop since no parallel reduction is available. We can emit the informational message instead of crashing the cli in such a case.
Fixes llvm#61842

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D147765

Author: Lewuathe

mlir/test/Dialect/Affine/SuperVectorize/vectorize_unsupported.mlir

@@ -0,0 +1,11 @@
+// RUN: mlir-opt %s -affine-super-vectorizer-test  -vectorize-affine-loop-nest -split-input-file 2>&1 |  FileCheck %s
+
+func.func @unparallel_loop_reduction_unsupported(%in: memref<256x512xf32>, %out: memref<256xf32>) {
+ // CHECK: Outermost loop cannot be parallel
+ %cst = arith.constant 1.000000e+00 : f32
+ %final_red = affine.for %j = 0 to 512 iter_args(%red_iter = %cst) -> (f32) {
+   %add = arith.addf %red_iter, %red_iter : f32
+   affine.yield %add : f32
+ }
+ return
+}

mlir/test/lib/Dialect/Affine/TestVectorizationUtils.cpp

@@ -92,7 +92,7 @@ struct VectorizerTestPass
   void testComposeMaps(llvm::raw_ostream &outs);
 
   /// Test for 'vectorizeAffineLoopNest' utility.
-  void testVecAffineLoopNest();
+  void testVecAffineLoopNest(llvm::raw_ostream &outs);
 };
 
 } // namespace
@@ -226,7 +226,7 @@ void VectorizerTestPass::testComposeMaps(llvm::raw_ostream &outs) {
 }
 
 /// Test for 'vectorizeAffineLoopNest' utility.
-void VectorizerTestPass::testVecAffineLoopNest() {
+void VectorizerTestPass::testVecAffineLoopNest(llvm::raw_ostream &outs) {
   std::vector<SmallVector<AffineForOp, 2>> loops;
   gatherLoops(getOperation(), loops);
 
@@ -239,6 +239,13 @@ void VectorizerTestPass::testVecAffineLoopNest() {
   VectorizationStrategy strategy;
   strategy.vectorSizes.push_back(4 /*vectorization factor*/);
   strategy.loopToVectorDim[outermostLoop] = 0;
+
+  ReductionLoopMap reductionLoops;
+  SmallVector<LoopReduction, 2> reductions;
+  if (!isLoopParallel(outermostLoop, &reductions)) {
+    outs << "Outermost loop cannot be parallel\n";
+    return;
+  }
   std::vector<SmallVector<AffineForOp, 2>> loopsToVectorize;
   loopsToVectorize.push_back({outermostLoop});
   (void)vectorizeAffineLoopNest(loopsToVectorize, strategy);
@@ -273,7 +280,7 @@ void VectorizerTestPass::runOnOperation() {
   }
 
   if (clTestVecAffineLoopNest)
-    testVecAffineLoopNest();
+    testVecAffineLoopNest(outs);
 
   if (!outs.str().empty()) {
     emitRemark(UnknownLoc::get(&getContext()), outs.str());