[MLIR] MemRefToEmitC: Lower memref.alloca to emitc.variable

mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp

@@ -82,6 +82,32 @@ struct ConvertStore final : public OpConversionPattern<memref::StoreOp> {
   }
 };
 
+struct ConvertAlloca final : public OpConversionPattern<memref::AllocaOp> {
+  using OpConversionPattern::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(memref::AllocaOp op, OpAdaptor operands,
+                  ConversionPatternRewriter &rewriter) const override {
+
+    if (!op.getType().hasStaticShape()) {
+      return rewriter.notifyMatchFailure(
+          op.getLoc(), "cannot transform alloca with dynamic shape");
+    }
+
+    if (op.getAlignment().value_or(1) > 1) {
+      // TODO: Allow alignment if it is not more than the natural alignment
+      // of the C array.
+      return rewriter.notifyMatchFailure(
+          op.getLoc(), "cannot transform alloca with alignment requirement");
+    }
+
+    auto resultTy = getTypeConverter()->convertType(op.getType());
+    auto noInit = emitc::OpaqueAttr::get(getContext(), "");
+    rewriter.replaceOpWithNewOp<emitc::VariableOp>(op, resultTy, noInit);
+    return success();
+  }
+};
+
 struct ConvertMemRefToEmitCPass
     : public impl::ConvertMemRefToEmitCBase<ConvertMemRefToEmitCPass> {
   void runOnOperation() override {
@@ -135,8 +161,8 @@ void mlir::populateMemRefToEmitCConversionPatterns(RewritePatternSet &patterns,
                                                                  converter);
   populateCallOpTypeConversionPattern(patterns, converter);
   populateReturnOpTypeConversionPattern(patterns, converter);
-  patterns.add<ConvertLoad>(converter, patterns.getContext());
-  patterns.add<ConvertStore>(converter, patterns.getContext());
+  patterns.add<ConvertLoad, ConvertStore, ConvertAlloca>(converter,
+                                                         patterns.getContext());
 }
 
 std::unique_ptr<OperationPass<>> mlir::createConvertMemRefToEmitCPass() {

mlir/test/Conversion/MemRefToEmitC/memref-to-emit-failed.mlir

@@ -22,3 +22,20 @@ func.func @memref_op(%arg0 : memref<2x4xf32>) {
   memref.copy %arg0, %arg0 : memref<2x4xf32> to memref<2x4xf32>
   return
 }
+
+// -----
+
+func.func @alloca_with_dynamic_shape() {
+  %0 = index.constant 1
+  // expected-error@+1 {{failed to legalize operation 'memref.alloca' that was explicitly marked illegal}}
+  %1 = memref.alloca(%0) : memref<4x?xf32>
+  return
+}
+
+// -----
+
+func.func @alloca_with_alignment() {
+  // expected-error@+1 {{failed to legalize operation 'memref.alloca' that was explicitly marked illegal}}
+  %1 = memref.alloca() {alignment = 64 : i64}: memref<4xf32>
+  return
+}

mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir

@@ -36,3 +36,12 @@ func.func @memref_load_store(%in: memref<4x8xf32>, %out: memref<3x5xf32>, %i: in
   memref.store %0, %out[%i, %j] : memref<3x5xf32>
   return
 }
+
+// -----
+
+// CHECK-LABEL: alloca
+func.func @alloca() {
+  // CHECK "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> !emitc.array<4x8xf32>
+  %0 = memref.alloca() : memref<4x8xf32>
+  return
+}