[mlir][Vector] Add support for 0-d shapes in extract-shape_cast folder (llvm#116650)

The extract <-> shape cast folder was conservatively asserting and
failing on 0-d vectors. This pr fixes this.

This pr also adds more tests for 0d cases and updates related tests to
better reflect what they test.

Author: Groverkss

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

@@ -1756,11 +1756,6 @@ static Value foldExtractFromShapeCast(ExtractOp extractOp) {
   if (!shapeCastOp)
     return Value();
 
-  // 0-D vectors not supported.
-  assert(!hasZeroDimVectors(extractOp) && "0-D vectors not supported");
-  if (hasZeroDimVectors(shapeCastOp))
-    return Value();
-
   // Get the nth dimension size starting from lowest dimension.
   auto getDimReverse = [](VectorType type, int64_t n) {
     return type.getShape().take_back(n + 1).front();

mlir/test/Dialect/Vector/canonicalize.mlir

@@ -782,30 +782,42 @@ func.func @fold_extract_shapecast(%arg0 : vector<5x1x3x2xf32>,
 
 // -----
 
-// CHECK-LABEL: fold_extract_shapecast_negative
-//       CHECK:   %[[V:.*]] = vector.shape_cast %{{.*}} : vector<16xf32> to vector<2x4x2xf32>
-//       CHECK:   %[[R:.*]] = vector.extract %[[V]][1] : vector<4x2xf32> from vector<2x4x2xf32>
-//       CHECK:   return %[[R]] : vector<4x2xf32>
-func.func @fold_extract_shapecast_negative(%arg0 : vector<16xf32>) -> vector<4x2xf32> {
-  %0 = vector.shape_cast %arg0 : vector<16xf32> to vector<2x4x2xf32>
-  %r = vector.extract %0[1] : vector<4x2xf32> from vector<2x4x2xf32>
-  return %r : vector<4x2xf32>
+// CHECK-LABEL: fold_extract_shapecast_0d_result
+//  CHECK-SAME: %[[IN:.*]]: vector<1x1x1xf32>
+//       CHECK:   %[[R:.*]] = vector.extract %[[IN]][0, 0, 0] : f32 from vector<1x1x1xf32>
+//       CHECK:   return %[[R]] : f32
+func.func @fold_extract_shapecast_0d_result(%arg0 : vector<1x1x1xf32>) -> f32 {
+  %0 = vector.shape_cast %arg0 : vector<1x1x1xf32> to vector<f32>
+  %r = vector.extract %0[] : f32 from vector<f32>
+  return %r : f32
 }
 
 // -----
 
-// CHECK-LABEL: dont_fold_0d_extract_shapecast
-//       CHECK:   %[[V:.*]] = vector.shape_cast %{{.*}} : vector<f32> to vector<1xf32>
-//       CHECK:   %[[R:.*]] = vector.extract %[[V]][0] : f32 from vector<1xf32>
+// CHECK-LABEL: fold_extract_shapecast_0d_source
+//  CHECK-SAME: %[[IN:.*]]: vector<f32>
+//       CHECK:   %[[R:.*]] = vector.extract %[[IN]][] : f32 from vector<f32>
 //       CHECK:   return %[[R]] : f32
-func.func @dont_fold_0d_extract_shapecast(%arg0 : vector<f32>) -> f32 {
+func.func @fold_extract_shapecast_0d_source(%arg0 : vector<f32>) -> f32 {
   %0 = vector.shape_cast %arg0 : vector<f32> to vector<1xf32>
   %r = vector.extract %0[0] : f32 from vector<1xf32>
   return %r : f32
 }
 
 // -----
 
+// CHECK-LABEL: fold_extract_shapecast_negative
+//       CHECK:   %[[V:.*]] = vector.shape_cast %{{.*}} : vector<16xf32> to vector<2x4x2xf32>
+//       CHECK:   %[[R:.*]] = vector.extract %[[V]][1] : vector<4x2xf32> from vector<2x4x2xf32>
+//       CHECK:   return %[[R]] : vector<4x2xf32>
+func.func @fold_extract_shapecast_negative(%arg0 : vector<16xf32>) -> vector<4x2xf32> {
+  %0 = vector.shape_cast %arg0 : vector<16xf32> to vector<2x4x2xf32>
+  %r = vector.extract %0[1] : vector<4x2xf32> from vector<2x4x2xf32>
+  return %r : vector<4x2xf32>
+}
+
+// -----
+
 // CHECK-LABEL: fold_extract_shapecast_to_shapecast
 //  CHECK-SAME: (%[[ARG:.+]]: vector<3x4xf32>)
 //       CHECK:   %[[R:.+]] = vector.shape_cast %[[ARG]] : vector<3x4xf32> to vector<12xf32>