[mlir][vector] Fix extract op canonicalization for 0d vector

[ThomasRaoux]

Summary

Fix ExtractOpFromBroadcast when the broadcast source is a 0d vector.

[nicolasvasilache]

Thanks!

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

LogicalResult matchAndRewrite(ExtractOp extractOp,
     };
     unsigned broadcastSrcRank = getRank(source.getType());
     unsigned extractResultRank = getRank(extractOp.getType());
     // We only consider the case where the rank of the source is less than or
     // equal to the rank of the extract dst. The other cases are handled in the
     // folding patterns.
     if (extractResultRank < broadcastSrcRank)
       return failure();
+
+    // Special case if broadcast src is a 0D vector.
+    if (extractResultRank == 0) {
+      assert(broadcastSrcRank == 0 && source.getType().isa<VectorType>());
+      rewriter.replaceOpWithNewOp<vector::ExtractElementOp>(extractOp, source);
+      return success();
+    }
     rewriter.replaceOpWithNewOp<vector::BroadcastOp>(
         extractOp, extractOp.getType(), source);
     return success();
   }
 };
 
 // Pattern to rewrite a ExtractOp(splat ConstantOp) -> ConstantOp.
 class ExtractOpSplatConstantFolder final : public OpRewritePattern<ExtractOp> {

mlir/test/Dialect/Vector/canonicalize.mlir

 func.func @fold_extract_broadcast(%a : f32) -> f32 {
   %b = vector.broadcast %a : f32 to vector<1x2x4xf32>
   %r = vector.extract %b[0, 1, 2] : vector<1x2x4xf32>
   return %r : f32
 }
 
 // -----
 
+// CHECK-LABEL: fold_extract_broadcast_0dvec
+//  CHECK-SAME:   %[[A:.*]]: vector<f32>
+//       CHECK:   %[[B:.+]] = vector.extractelement %[[A]][] : vector<f32>
+//       CHECK:   return %[[B]] : f32
+func.func @fold_extract_broadcast_0dvec(%a : vector<f32>) -> f32 {
+  %b = vector.broadcast %a : vector<f32> to vector<1x2x4xf32>
+  %r = vector.extract %b[0, 1, 2] : vector<1x2x4xf32>
+  return %r : f32
+}
+
+// -----
+
 // CHECK-LABEL: fold_extract_broadcast_negative
 //       CHECK:   vector.broadcast %{{.*}} : vector<1x1xf32> to vector<1x1x4xf32>
 //       CHECK:   vector.extract %{{.*}}[0, 0] : vector<1x1x4xf32>
 func.func @fold_extract_broadcast_negative(%a : vector<1x1xf32>) -> vector<4xf32> {
   %b = vector.broadcast %a : vector<1x1xf32> to vector<1x1x4xf32>
   %r = vector.extract %b[0, 0] : vector<1x1x4xf32>
   return %r : vector<4xf32>
 }