[mlir][vector] Support for extracting 1-element vectors in VectorExtractOpConversion (#107549)

This patch adds support for converting `vector.extract` that extract
1-element vectors into LLVM, fixing a crash in such cases.
E.g., `vector.extract %1[0]: vector<1xf32> from vector<2xf32>`. Fix
#61372.

Author: CoTinker

mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp

@@ -1104,7 +1104,10 @@ class VectorExtractOpConversion
     }
 
     // One-shot extraction of vector from array (only requires extractvalue).
-    if (isa<VectorType>(resultType)) {
+    // Except for extracting 1-element vectors.
+    if (isa<VectorType>(resultType) &&
+        position.size() !=
+            static_cast<size_t>(extractOp.getSourceVectorType().getRank())) {
       if (extractOp.hasDynamicPosition())
         return failure();
 

mlir/test/Conversion/VectorToLLVM/vector-to-llvm.mlir

@@ -1130,6 +1130,30 @@ func.func @extract_scalar_from_vec_1d_f32_scalable(%arg0: vector<[16]xf32>) -> f
 
 // -----
 
+func.func @extract_vec_1e_from_vec_1d_f32(%arg0: vector<16xf32>) -> vector<1xf32> {
+  %0 = vector.extract %arg0[15]: vector<1xf32> from vector<16xf32>
+  return %0 : vector<1xf32>
+}
+// CHECK-LABEL: @extract_vec_1e_from_vec_1d_f32(
+//  CHECK-SAME:   %[[A:.*]]: vector<16xf32>)
+//       CHECK:   %[[T0:.*]] = llvm.mlir.constant(15 : i64) : i64
+//       CHECK:   %[[T1:.*]] = llvm.extractelement %[[A]][%[[T0]] : i64] : vector<16xf32>
+//       CHECK:   %[[T2:.*]] = builtin.unrealized_conversion_cast %[[T1]] : f32 to vector<1xf32>
+//       CHECK:   return %[[T2]] : vector<1xf32>
+
+func.func @extract_vec_1e_from_vec_1d_f32_scalable(%arg0: vector<[16]xf32>) -> vector<1xf32> {
+  %0 = vector.extract %arg0[15]: vector<1xf32> from vector<[16]xf32>
+  return %0 : vector<1xf32>
+}
+// CHECK-LABEL: @extract_vec_1e_from_vec_1d_f32_scalable(
+//  CHECK-SAME:   %[[A:.*]]: vector<[16]xf32>)
+//       CHECK:   %[[T0:.*]] = llvm.mlir.constant(15 : i64) : i64
+//       CHECK:   %[[T1:.*]] = llvm.extractelement %[[A]][%[[T0]] : i64] : vector<[16]xf32>
+//       CHECK:   %[[T2:.*]] = builtin.unrealized_conversion_cast %[[T1]] : f32 to vector<1xf32>
+//       CHECK:   return %[[T2]] : vector<1xf32>
+
+// -----
+
 func.func @extract_scalar_from_vec_1d_index(%arg0: vector<16xindex>) -> index {
   %0 = vector.extract %arg0[15]: index from vector<16xindex>
   return %0 : index