[mlir][linalg] Fix crash caused by nullptr dereference (llvm#163132)

This PR fixes a crash caused by nullptr dereference in
`isContractionBody` if reductionOp is nullptr. Fixes llvm#162772.

Author: CoTinker

mlir/lib/Dialect/Linalg/IR/LinalgInterfaces.cpp

@@ -315,7 +315,8 @@ bool mlir::linalg::detail::isContractionBody(
 
   Value yielded = getSourceSkipUnary(terminator->getOperand(0));
   Operation *reductionOp = yielded.getDefiningOp();
-  if (reductionOp->getNumResults() != 1 || reductionOp->getNumOperands() != 2) {
+  if (!reductionOp || reductionOp->getNumResults() != 1 ||
+      reductionOp->getNumOperands() != 2) {
     errs << "expected reduction op to be binary";
     return false;
   }

mlir/test/Dialect/Linalg/match-ops-interpreter.mlir

@@ -1011,6 +1011,20 @@ module attributes { transform.target_tag = "start_here" } {
     } -> tensor<1x1x4xf32>
     return
   }
+
+  func.func @generic_none(%arg0: tensor<128x128xi32>, %arg1: tensor<128x128xi32>, %arg2: tensor<128x128xi32>) {
+    %0 = linalg.generic {
+      indexing_maps = [affine_map<(d0, d1, d2) -> (d0, d2)>,
+                       affine_map<(d0, d1, d2) -> (d2, d1)>,
+                       affine_map<(d0, d1, d2) -> (d0, d1)>],
+      iterator_types = ["parallel", "parallel", "reduction"]}
+      ins(%arg0, %arg1 : tensor<128x128xi32>, tensor<128x128xi32>)
+      outs(%arg2 : tensor<128x128xi32>) {
+      ^bb0(%in: i32, %in_0: i32, %out: i32):
+        linalg.yield %out : i32
+      } -> tensor<128x128xi32>
+    return
+  }
 }
 
 // -----