[mlir][xegpu] Add support for distributing gpu.barrier (llvm#145434)

Author: charithaintc

mlir/lib/Dialect/XeGPU/Transforms/XeGPUSubgroupDistribute.cpp

@@ -455,6 +455,14 @@ struct LoadNdDistribution final : public gpu::WarpDistributionPattern {
     if (!operand)
       return rewriter.notifyMatchFailure(
           subgroupOp, "warp result is not a xegpu::LoadNd op");
+    // Make sure the load op is the last operation in the warp op body. This
+    // ensure that load op is not sinked earlier violating any barrier
+    // synchronizations.
+    auto yield = cast<gpu::YieldOp>(
+        subgroupOp.getBodyRegion().getBlocks().begin()->getTerminator());
+    Operation *lastNode = yield->getPrevNode();
+    if (!dyn_cast_or_null<xegpu::LoadNdOp>(lastNode))
+      return failure();
 
     auto loadOp = operand->get().getDefiningOp<xegpu::LoadNdOp>();
     xegpu::TensorDescType tensorDescTy = loadOp.getTensorDescType();
@@ -782,6 +790,29 @@ struct PrefetchNdDistribution final : public gpu::WarpDistributionPattern {
   }
 };
 
+/// Sink a gpu::BarrierOp at the end of enclosing `gpu.warp_execute_on_lane_0`
+/// region. This will simply move the barrier op outside of the warp op.
+struct GpuBarrierDistribution final : public gpu::WarpDistributionPattern {
+  using gpu::WarpDistributionPattern::WarpDistributionPattern;
+  LogicalResult matchAndRewrite(gpu::WarpExecuteOnLane0Op subgroupOp,
+                                PatternRewriter &rewriter) const override {
+    auto yield = cast<gpu::YieldOp>(
+        subgroupOp.getBodyRegion().getBlocks().begin()->getTerminator());
+    Operation *lastNode = yield->getPrevNode();
+    // The last node must be a gpu::BarrierOp.
+    auto barrierOp = dyn_cast_or_null<gpu::BarrierOp>(lastNode);
+    if (!barrierOp)
+      return failure();
+    // Move the barrier op outside of the warp op.
+    rewriter.setInsertionPointAfter(subgroupOp);
+    rewriter.create<gpu::BarrierOp>(
+        barrierOp.getLoc(), barrierOp->getResultTypes(),
+        barrierOp->getOperands(), barrierOp->getAttrs());
+    rewriter.eraseOp(barrierOp);
+    return success();
+  }
+};
+
 } // namespace
 
 namespace {
@@ -796,7 +827,8 @@ void xegpu::populateXeGPUSubgroupDistributePatterns(
     RewritePatternSet &patterns) {
   patterns.add<CreateNdDescDistribution, StoreNdDistribution,
                LoadNdDistribution, DpasDistribution, PrefetchNdDistribution,
-               UpdateNdOffsetDistribution>(patterns.getContext());
+               UpdateNdOffsetDistribution, GpuBarrierDistribution>(
+      patterns.getContext());
 }
 
 void XeGPUSubgroupDistributePass::runOnOperation() {

mlir/test/Dialect/XeGPU/subgroup-distribute.mlir

@@ -278,3 +278,22 @@ gpu.module @test {
     gpu.return
   }
 }
+
+// -----
+// CHECK-LABEL: gpu.func @gpu_barrier({{.*}}) {
+// CHECK: %[[T0:.*]] = xegpu.create_nd_tdesc %{{.*}} : memref<256xf16> -> !xegpu.tensor_desc<16xf16>
+// CHECK-NEXT: %[[T1:.*]] = xegpu.load_nd %[[T0]]  : !xegpu.tensor_desc<16xf16> -> vector<1xf16>
+// CHECK-NEXT: gpu.barrier
+// CHECK-NEXT: %[[T2:.*]] = xegpu.create_nd_tdesc %{{.*}} : memref<256xf16> -> !xegpu.tensor_desc<16xf16>
+// CHECK-NEXT: xegpu.store_nd %[[T1]], %[[T2]] : vector<1xf16>, !xegpu.tensor_desc<16xf16>
+gpu.module @test {
+  gpu.func @gpu_barrier(%arg0: memref<256xf16>, %arg1: memref<256xf16>) {
+    %c0 = arith.constant 0 : index
+    %0 = xegpu.create_nd_tdesc %arg0[%c0] : memref<256xf16> -> !xegpu.tensor_desc<16xf16, #xegpu.layout<lane_layout = [16], lane_data = [1]>>
+    %1 = xegpu.load_nd %0  {layout_result_0 = #xegpu.layout<lane_layout = [16], lane_data = [1]>} : !xegpu.tensor_desc<16xf16, #xegpu.layout<lane_layout = [16], lane_data = [1]>> -> vector<16xf16>
+    gpu.barrier
+    %2 = xegpu.create_nd_tdesc %arg1[%c0] : memref<256xf16> -> !xegpu.tensor_desc<16xf16, #xegpu.layout<lane_layout = [16], lane_data = [1]>>
+    xegpu.store_nd %1, %2 : vector<16xf16>, !xegpu.tensor_desc<16xf16, #xegpu.layout<lane_layout = [16], lane_data = [1]>>
+    gpu.return
+  }
+}