[MLIR] Add missing check for unsupported affine dependence analysis

[bondhugula]

Summary

Add missing check in affine dependence analysis when dependence analysis
isn't possible due to the ops being in different affine scopes. The
lack of such a check could lead to a crash or incorrect behavior in
several dependent utilities.

mlir/lib/Dialect/Affine/Analysis/AffineAnalysis.cpp

if (srcAccess.memref != dstAccess.memref)
     return DependenceResult::NoDependence;
 
   // Return 'NoDependence' if one of these accesses is not an
   // AffineWriteOpInterface.
   if (!allowRAR && !isa<AffineWriteOpInterface>(srcAccess.opInst) &&
       !isa<AffineWriteOpInterface>(dstAccess.opInst))
     return DependenceResult::NoDependence;
 
+  // We can't analyze further if the ops lie in different affine scopes.
+  if (getAffineScope(srcAccess.opInst) != getAffineScope(dstAccess.opInst))
+    return DependenceResult::Failure;
+
   // Create access relation from each MemRefAccess.
   FlatAffineRelation srcRel, dstRel;
   if (failed(srcAccess.getAccessRelation(srcRel)))
     return DependenceResult::Failure;
   if (failed(dstAccess.getAccessRelation(dstRel)))
     return DependenceResult::Failure;
 
   FlatAffineValueConstraints srcDomain = srcRel.getDomainSet();

mlir/test/Dialect/Affine/scalrep.mlir

test.affine_scope {
       // The addf above will get the forwarded value from the store on
       // %memref_0 above which is being loaded into %30..
       // CHECK: arith.addf %[[A]],
       "terminate"() : () -> ()
     }
   }
   return
 }
+
+// No scalrep will be performed here but we ensure dependence correctly fails.
+
+// CHECK-LABEL: func @affine_load_store_in_different_scopes
+func.func @affine_load_store_in_different_scopes() -> memref<1xf32> {
+  %A = memref.alloc() : memref<1xf32>
+  %cf0 = arith.constant 0.0 : f32
+  %cf5 = arith.constant 5.0 : f32
+
+  affine.store %cf0, %A[0] : memref<1xf32>
+  test.affine_scope {
+    affine.store %cf5, %A[0] : memref<1xf32>
+    "test.terminate"() : () -> ()
+  }
+  %v = affine.load %A[0] : memref<1xf32>
+  // CHECK:      affine.store
+  // CHECK-NEXT: test.affine_scope
+  // CHECK:        affine.store
+  // CHECK:      affine.load
+  return %A : memref<1xf32>
+}