Template Arguments for Generators?

[FabianSchuetze]

Can I use template parameters for a generator?

For example, consider the following code:

template <size_t W, size_t H>
class ConvolutionLayer : public Generator<ConvolutionLayer<CW, H>>

The template parameters W and H are then used to set the bounds of the input and output buffers and to inform the auto-schedulers. For example, this specifying height and width is done in the conv_layer and and can be specified like so constexpr int W{10}, H{10}.

I call the HALIDE_REGISTER_GENERATOR macro with:

HALIDE_REGISTER_GENERATOR(ConvolutionLayer<10, 10>, conv_layer)

The generation then fails with several compile errors. I looked in the tutorials and apps to find template argument usage but couldn't find it.

I have tried using the GeneratorParams but they also failed with some compiler error and I am not sure GeneratorParams are meant to be used for this.

[abadams]

Normally you'd use GeneratorParams instead of template parameters for things like that, but sometimes it is more convenient to use template parameters. I think the problem is that the preprocessor doesn't know about angle brackets, so it sees that as a three-argument macro call, where the arguments are ConvolutionLayer<10, 10>, and conv_layer. Try this:

HALIDE_REGISTER_GENERATOR((ConvolutionLayer<10, 10>), conv_layer)

and if that doesn't work try this:

using ConvolutionLayer_10_10 = ConvolutionLayer<10, 10>;
HALIDE_REGISTER_GENERATOR(ConvolutionLayer_10_10, conv_layer)

[FabianSchuetze]

Thanks a lot for the kind and detailed reply!

I couldn't make it work unfortunately. Here's the patch I applied to the resize_generator.cpp in the resize app:

diff --git a/apps/resize/resize_generator.cpp b/apps/resize/resize_generator.cpp
index 5b17b3dcc..dbd0ed9f4 100644
--- a/apps/resize/resize_generator.cpp
+++ b/apps/resize/resize_generator.cpp
@@ -54,7 +54,8 @@ static KernelInfo kernel_info[] = {
     {"cubic", 4, kernel_cubic},
     {"lanczos", 6, kernel_lanczos}};
 
-class Resize : public Halide::Generator<Resize> {
+template <size_t channels>
+class ResizeTemplate : public Halide::Generator<ResizeTemplate<channels>> {
 public:
     GeneratorParam<InterpolationType> interpolation_type{"interpolation_type", Cubic, {{"box", Box}, {"linear", Linear}, {"cubic", Cubic}, {"lanczos", Lanczos}}};
 
@@ -63,9 +64,9 @@ public:
     // resample in x and in y).
     GeneratorParam<bool> upsample{"upsample", false};
 
-    Input<Buffer<void, 3>> input{"input"};
+    Input<Buffer<void, channels>> input{"input"};
     Input<float> scale_factor{"scale_factor"};
-    Output<Buffer<void, 3>> output{"output"};
+    Output<Buffer<void, channels>> output{"output"};
 
     // Common Vars
     Var x{"x"}, y{"y"}, c{"c"}, k{"k"};
@@ -237,4 +238,5 @@ public:
     }
 };
 
+using Resize = ResizeTemplate<3>;
 HALIDE_REGISTER_GENERATOR(Resize, resize);

and the errors I get are:

➜  resize git:(resize_android) ✗ HL_TARGET=host make
g++ -O3 -std=c++17 -I /home/fabian/Documents/work/github/Halide/distrib/include/ -I /home/fabian/Documents/work/github/Halide/distrib/tools/  -Wall -Werror -Wno-unused-function -Wcast-qual -Wignored-qualifiers -Wno-comment -Wsign-compare -Wno-unknown-warning-option -Wno-psabi -fno-rtti resize_generator.cpp /home/fabian/Documents/work/github/Halide/distrib/tools/GenGen.cpp -o bin/host/resize.generator -Wl,-rpath,/home/fabian/Documents/work/github/Halide/distrib/lib/ -L /home/fabian/Documents/work/github/Halide/distrib/lib/ -lHalide -ldl -lpthread -lz -Wl,--no-as-needed -lautoschedule_adams2019 -Wl,--as-needed
resize_generator.cpp:67:5: error: ‘Input’ does not name a type
   67 |     Input<Buffer<void, channels>> input{"input"};
      |     ^~~~~
resize_generator.cpp:68:5: error: ‘Input’ does not name a type
   68 |     Input<float> scale_factor{"scale_factor"};
      |     ^~~~~
resize_generator.cpp:69:5: error: ‘Output’ does not name a type
   69 |     Output<Buffer<void, channels>> output{"output"};
      |     ^~~~~~
resize_generator.cpp: In member function ‘void ResizeTemplate<channels>::generate()’:
resize_generator.cpp:88:41: error: there are no arguments to ‘input’ that depend on a template parameter, so a declaration of ‘input’ must be available [-fpermissive]
   88 |         as_float(x, y, c) = cast<float>(input(x, y, c));
      |                                         ^~~~~
resize_generator.cpp:88:41: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
resize_generator.cpp:96:57: error: ‘scale_factor’ was not declared in this scope
   96 |         Expr inverse_scale_factor = strict_float(1.0f / scale_factor);
      |                                                         ^~~~~~~~~~~~
resize_generator.cpp:115:32: error: ‘input’ was not declared in this scope; did you mean ‘int’?
  115 |         beginx = clamp(beginx, input.dim(0).min(), input.dim(0).max() + 1 - kernel_taps);
      |                                ^~~~~
      |                                int
resize_generator.cpp:145:13: error: there are no arguments to ‘output’ that depend on a template parameter, so a declaration of ‘output’ must be available [-fpermissive]
  145 |             output(x, y, c) = clamp(resized(x, y, c), 0.0f, 1.0f);
      |             ^~~~~~
resize_generator.cpp:147:13: error: there are no arguments to ‘output’ that depend on a template parameter, so a declaration of ‘output’ must be available [-fpermissive]
  147 |             output(x, y, c) = saturating_cast(input.type(), resized(x, y, c));
      |             ^~~~~~
resize_generator.cpp: In member function ‘void ResizeTemplate<channels>::schedule()’:
resize_generator.cpp:152:25: error: ‘natural_vector_size’ was not declared in this scope
  152 |         const int vec = natural_vector_size<float>();
      |                         ^~~~~~~~~~~~~~~~~~~
resize_generator.cpp:152:45: error: expected primary-expression before ‘float’
  152 |         const int vec = natural_vector_size<float>();
      |                                             ^~~~~
resize_generator.cpp:174:25: error: ‘output’ was not declared in this scope
  174 |             .compute_at(output, y)
      |                         ^~~~~~
resize_generator.cpp:208:9: error: ‘input’ was not declared in this scope; did you mean ‘int’?
  208 |         input.dim(0).set_stride(Expr());
      |         ^~~~~
      |         int
resize_generator.cpp: In instantiation of ‘void ResizeTemplate<channels>::generate() [with long unsigned int channels = 3]’:
/home/fabian/Documents/work/github/Halide/distrib/include/Halide.h:29554:20:   required from ‘void Halide::Generator<T>::call_generate_impl() [with T = ResizeTemplate<3>]’
/home/fabian/Documents/work/github/Halide/distrib/include/Halide.h:29579:15:   required from ‘void Halide::Generator<T>::call_generate() [with T = ResizeTemplate<3>]’
/home/fabian/Documents/work/github/Halide/distrib/include/Halide.h:29578:10:   required from here
resize_generator.cpp:88:46: error: ‘input’ was not declared in this scope; did you mean ‘Input’?
   88 |         as_float(x, y, c) = cast<float>(input(x, y, c));
      |                                         ~~~~~^~~~~~~~~
      |                                         Input
resize_generator.cpp:145:19: error: ‘output’ was not declared in this scope; did you mean ‘Output’?
  145 |             output(x, y, c) = clamp(resized(x, y, c), 0.0f, 1.0f);
      |             ~~~~~~^~~~~~~~~
      |             Output
At global scope:
cc1plus: note: unrecognized command-line option ‘-Wno-unknown-warning-option’ may have been intended to silence earlier diagnostics

Do you know if there's anything I'm doing wrong?

[abadams]

You should really be using a GeneratorParam for something like a channel count. The only reason for it to be a template parameter is if you need the channel count to be constexpr for some other reason (e.g. you call a function written by someone else that's templated on the channel count).

However, pressing on, this is a c++ CRTP wart. When you use CRTP like this:

template<typename T>
class Foo : public Generator<Foo<T>> {

Then names from the base class don't get inherited by default. It's super annoying. For members you typically just add a this-> before them, but your problem is with types that belong to the Generator base class. I think this can be solved with some using statements in the class, but the simplest solution is to replace the types Input and Output with GeneratorInput and GeneratorOutput. It's the same thing.

[abadams]

Oh, and replace natural_vector_size with this->natural_vector_size, because that's a member of the base class.

[FabianSchuetze]

Thanks again for the answer!