[MLIR][MHLO] Add pattern to inline broadcasted shapes

Simplify reasoning about `cstr_broadcastable` ops in the
`mhlo-move-up-dynamic-broadcasts-for-fusion` pass.

PiperOrigin-RevId: 365560893

lib/Dialect/mhlo/transforms/move_up_dynamic_broadcasts_for_fusion.cc

@@ -69,6 +69,33 @@ struct ShapeReificationPattern : public OpRewritePattern<shape::ShapeOfOp> {
   }
 };
 
+template <typename OpTy>
+struct InlineBroadcastedShapeOperandsPattern : public OpRewritePattern<OpTy> {
+  using OpRewritePattern<OpTy>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(OpTy op,
+                                PatternRewriter &rewriter) const override {
+    // Find all the shape operands, direct and indirect.
+    SmallVector<Value, 8> inlined_operands;
+    for (Value direct : op->getOperands()) {
+      if (auto bcast_op = direct.getDefiningOp<shape::BroadcastOp>()) {
+        for (Value indirect : bcast_op->getOperands())
+          inlined_operands.push_back(indirect);
+      } else {
+        inlined_operands.push_back(direct);
+      }
+    }
+
+    // Only rewrite if it makes a difference.
+    if (inlined_operands.size() == op.getNumOperands()) return failure();
+
+    // Inline shape operands.
+    rewriter.replaceOpWithNewOp<OpTy>(op, op->getResultTypes(),
+                                      inlined_operands, op->getAttrs());
+    return success();
+  }
+};
+
 // TODO(frgossen): Only move up broadcasting operations if there is a consumer.
 struct MoveUpBroadcastInDimOpPattern
     : public OpRewritePattern<DynamicBroadcastInDimOp> {
@@ -124,12 +151,9 @@ struct MoveUpDynamicBroadcastsForFusionPass
   }
 
   void runOnFunction() override {
-    // Populate rewrite patterns.
     MLIRContext *ctx = &getContext();
     RewritePatternSet patterns(ctx);
     mhlo::PopulateMoveUpDynamicBroadcastsForFusionPatterns(ctx, &patterns);
-
-    // Apply transformation.
     if (failed(
             applyPatternsAndFoldGreedily(getFunction(), std::move(patterns)))) {
       return signalPassFailure();
@@ -142,8 +166,10 @@ struct MoveUpDynamicBroadcastsForFusionPass
 void PopulateMoveUpDynamicBroadcastsForFusionPatterns(
     MLIRContext *context, OwningRewritePatternList *patterns) {
   // clang-format off
-  patterns->insert<ShapeReificationPattern,
-                   MoveUpBroadcastInDimOpPattern>(context);
+  patterns->insert<
+      InlineBroadcastedShapeOperandsPattern<shape::CstrBroadcastableOp>,
+      MoveUpBroadcastInDimOpPattern,
+      ShapeReificationPattern>(context);
   // clang-format on
 }
 

tests/move_up_dynamic_broadcasts_for_fusion.mlir

@@ -97,3 +97,18 @@ func @cast_sub(%arg0: tensor<?x32xi16>, %arg1: tensor<?x?x32xf16>)
   }
   return %4 : tensor<?x?x32xf16>
 }
+
+// -----
+
+// CHECK-LABEL: @inline_bcasted_shape_operands
+// CHECK-SAME: (%[[A:.*]]: tensor<?xindex>, %[[B:.*]]: tensor<?xindex>, %[[C:.*]]: tensor<?xindex>)
+func @inline_bcasted_shape_operands(%a : tensor<?xindex>, %b : tensor<?xindex>,
+    %c : tensor<?xindex>) -> !shape.witness {
+  // CHECK-NOT: shape.broadcast
+  // CHECK:     %[[WITNESS:.*]] = shape.cstr_broadcastable %[[A]], %[[B]], %[[C]]
+  // CHECK:     return %[[WITNESS]] : !shape.witness
+  %0 = shape.broadcast %a, %b : tensor<?xindex>, tensor<?xindex>
+      -> tensor<?xindex>
+  %1 = shape.cstr_broadcastable %0, %c : tensor<?xindex>, tensor<?xindex>
+  return %1 : !shape.witness
+}