cuda: fix windowing test with cuda

Fixes #422.

This commit ensures that the allocation clearing logic is applied to
the CUDA backend as well. The windowing test caught this because TACO
was automatically parallelizing the loop onto the GPU.

Author: Rohan Yadav

src/codegen/codegen_cuda.cpp

@@ -1096,6 +1096,20 @@ void CodeGen_CUDA::visit(const Allocate* op) {
   op->num_elements.accept(this);
   parentPrecedence = TOP;
   stream << "));" << endl;
+  // If the operation wants the input cleared, then memset it to zero.
+  if (op->clear) {
+    doIndent();
+    stream << "gpuErrchk(cudaMemset(";
+    op->var.accept(this);
+    stream << variable_name;
+    stream << ", 0, ";
+    stream << "sizeof(" << elementType << ")";
+    stream << " * ";
+    parentPrecedence = MUL;
+    op->num_elements.accept(this);
+    parentPrecedence = TOP;
+    stream << "));" << endl;
+  }
 
   if(op->is_realloc) {
     doIndent();