[VectorDistribution] Add distribution for trivial vector.extract (ire…

…e-org#19318)

This patch adds a distribution pattern for vector.extract when the list
of indices is zero. This arises in the case of a scalar extract for 0-d
vectors.

compiler/src/iree/compiler/Codegen/Common/GPU/GPUDistributionPatterns.cpp

@@ -303,10 +303,37 @@ struct DistributeGather final : OpDistributionPattern<vector::GatherOp> {
   }
 };
 
+/// Distribute a 0-rank vector to scalar vector.extract conversion.
+struct DistributeTrivialExtract final
+    : OpDistributionPattern<vector::ExtractOp> {
+  using OpDistributionPattern::OpDistributionPattern;
+
+  LogicalResult matchAndRewrite(vector::ExtractOp extractOp,
+                                DistributionSignature &signature,
+                                PatternRewriter &rewriter) const override {
+    if (extractOp.getSourceVectorType().getRank() != 0) {
+      return rewriter.notifyMatchFailure(
+          extractOp, "Only 0-rank vector extractions supported");
+    }
+
+    VectorValue source = extractOp.getVector();
+    VectorLayoutInterface sourceLayout = signature[source];
+
+    Value distributed = rewriter.create<vector::ExtractOp>(
+        extractOp.getLoc(), getDistributed(rewriter, source, sourceLayout),
+        ArrayRef<int64_t>{});
+
+    replaceOpWithDistributedValues(rewriter, extractOp, distributed);
+
+    return success();
+  }
+};
+
 } // namespace
 
 void populateGPUDistributionPatterns(RewritePatternSet &patterns) {
-  patterns.add<DistributeConstants, DistributeScfFor>(patterns.getContext());
+  patterns.add<DistributeConstants, DistributeScfFor, DistributeTrivialExtract>(
+      patterns.getContext());
   // Elementwise patterns.
   patterns.add<DistributeElementwise>(patterns.getContext());
   patterns.add<DistributeTrivialLayoutConversions>(patterns.getContext());

compiler/src/iree/compiler/Codegen/Common/GPU/test/gpu_vector_distribution.mlir

@@ -96,6 +96,23 @@ func.func @distribute_scf_for_0d(%a: vector<i32>, %b: vector<i32>) -> vector<i32
   return %out : vector<i32>
 }
 
+// CHECK-LABEL: @distribute_scalar_extract
+func.func @distribute_scalar_extract(%a: f16, %b: vector<f16>) -> f16 {
+  %c0 = arith.constant 0 : index
+  %cst_0 = arith.constant 0.0 : f16
+  // CHECK: %[[ROOT:.*]] = arith.constant dense<0.000000e+00> : vector<f16>
+  %root = arith.constant dense<0.0> : vector<f16>
+  %rootl = iree_vector_ext.to_layout %root to layout(#layout_0d) : vector<f16>
+  // CHECK-DAG: %[[B:.*]] = iree_vector_ext.to_simt %{{.*}} : vector<f16> -> vector<f16>
+  // CHECK-DAG: %[[C:.*]] = arith.mulf %[[B]], %[[ROOT]] : vector<f16>
+  // CHECK-DAG: %[[SCALAR:.*]] = vector.extract %[[C]][] : f16 from vector<f16>
+  %c = arith.mulf %rootl, %b : vector<f16>
+  %scalar = vector.extract %c[] : f16 from vector<f16>
+  // CHECK-DAG: %[[D:.*]] = arith.addf %[[SCALAR]], %{{.*}} : f16
+  %d = arith.addf %scalar, %a : f16
+  return %d : f16
+}
+
 builtin.module attributes { transform.with_named_sequence } {
   transform.named_sequence @__transform_main(%variant_op: !transform.any_op {transform.readonly}) {
     %top_level_func = transform.structured.match ops{["func.func"]} in %variant_op : (!transform.any_op) -> !transform.any_op