[mlir][Linalg] Avoid generating illegal operations during elementwise fusion.

In some cases, fusion can produce illegal operations if after fusion
the range of some of the loops cannot be computed from shapes of its
operands. Check for this case and abort the fusion if this happens.

Differential Revision: https://reviews.llvm.org/D117602

Author: MaheshRavishankar

mlir/lib/Dialect/Linalg/Transforms/ElementwiseOpFusion.cpp

@@ -318,6 +318,13 @@ fuseElementwiseOpsImpl(GenericOp producer, OpOperand *consumerOpOperand,
       consumer.iterator_types(),
       /*doc=*/nullptr,
       /*library_call=*/nullptr);
+  if (!fusedOp.getShapesToLoopsMap()) {
+    // Fused op has invalid indexing maps. Typically this means something is off
+    // in the input, but going ahead here would result in verification errors.
+    // So cleanup and abort.
+    rewriter.eraseOp(fusedOp);
+    return llvm::None;
+  }
 
   // Construct an AffineMap from consumer loops to producer loops.
   // consumer loop -> tensor index

mlir/test/Dialect/Linalg/fusion-elementwise-ops.mlir

@@ -945,3 +945,33 @@ func @no_fusion_missing_reduction_shape(%arg0: tensor<f32>, %arg1: index) -> ten
   } -> tensor<?xf32>
   return %8 : tensor<?xf32>
 }
+
+// -----
+
+func @illegal_fusion(%arg0 : tensor<5000xi64>, %arg1 : tensor<5000xi32>) -> tensor<5000xi32> {
+  %c1_i32 = arith.constant 1 : i32
+  %0 = linalg.generic {
+        indexing_maps = [affine_map<(d0) -> (d0)>],
+        iterator_types = ["parallel"]}
+        outs(%arg0 : tensor<5000xi64>) {
+        ^bb0(%arg3: i64):  // no predecessors
+          %22 = linalg.index 0 : index
+          %23 = arith.index_cast %22 : index to i64
+          linalg.yield %23 : i64
+        } -> tensor<5000xi64>
+  %1 = linalg.init_tensor [5000] : tensor<5000xi32>
+  %2 = linalg.generic {
+        indexing_maps = [affine_map<(d0, d1) -> (d0)>, affine_map<(d0, d1) -> (d1)>],
+        iterator_types = ["parallel", "parallel"]}
+        ins(%0 : tensor<5000xi64>) outs(%1 : tensor<5000xi32>) {
+        ^bb0(%arg3: i64, %arg5: i32):  // no predecessors
+          %22 = arith.index_cast %arg3 : i64 to index
+          %23 = tensor.extract %arg1[%22] : tensor<5000xi32>
+          linalg.yield %23 : i32
+        } -> tensor<5000xi32>
+  return %2 : tensor<5000xi32>
+}
+// CHECK-LABEL: func @illegal_fusion(
+//       CHECK:   %[[PRODUCER:.+]] = linalg.generic
+//       CHECK:    linalg.generic
+//   CHECK-SAME:       ins(%[[PRODUCER]]