Parameterize epsilon for layernorm kernel (#1367)

This PR allows for other values of epsilon to be matched when finding layernorm. Similarly, the calculation now uses the variable for epsilon.

src/include/migraphx/match/layernorm.hpp

@@ -50,8 +50,8 @@ struct layernorm_matcher
     {
         return f("div")(arg(0)(x_minus_mean()),
 
-                        arg(1)(skip_broadcasts(f("sqrt")(
-                            arg(0)(f("add")(either_arg(0, 1)(variance(), has_value(1e-12f))))))));
+                        arg(1)(skip_broadcasts(f("sqrt")(arg(0)(
+                            f("add")(either_arg(0, 1)(variance(), is_constant().bind("eps"))))))));
     }
 
     auto matcher() const { return layernorm_onnx(); }

src/targets/gpu/jit/layernorm.cpp

@@ -52,7 +52,7 @@ __global__ void ${kernel}(${params})
 {
     auto idx = make_index();
     transform_args(make_tensors(), rotate_last(), ${transformers})(${args})([](auto... xs) {
-        ${layernorm}<${axis}>(${post}, xs...);
+        ${layernorm}<${axis}>(${post}, ${eps}, xs...);
     });
 }
     
@@ -90,6 +90,7 @@ struct layernorm_compiler : compiler<layernorm_compiler>
         options.output      = inputs.back();
         options.inputs      = inputs;
         options.kernel_name = v.get("kernel", "layernorm_kernel");
+        auto eps            = v.get("epsilon", 1e-12f);
 
         auto src = interpolate_string(layernorm_kernel,
                                       {{"kernel", options.kernel_name},
@@ -99,7 +100,8 @@ struct layernorm_compiler : compiler<layernorm_compiler>
                                        {"post", v.get("post", std::string{"op::id{}"})},
                                        {"preamble", v.get("preamble", std::string{})},
                                        {"layernorm", v.get("layernorm", std::string{"layernorm"})},
-                                       {"axis", to_string(axis)}});
+                                       {"axis", to_string(axis)},
+                                       {"eps", to_string(eps)}});
 
         return compile_hip_code_object(src, options);
     }

src/targets/gpu/kernels/include/migraphx/kernels/layernorm.hpp

@@ -43,7 +43,7 @@ template <index_int Axis,
           class Input2,
           class... Inputs>
 __device__ void generic_binary_layernorm(
-    F compute, BinOp op, Output output, Input1 input1, Input2 input2, Inputs... inputs)
+    F compute, BinOp op, float eps, Output output, Input1 input1, Input2 input2, Inputs... inputs)
 {
     using reduce_output = reduce::with_axis<Input1, Axis>;
     reduce::block::run<reduce_output>([&](auto, auto r) {
@@ -58,29 +58,31 @@ __device__ void generic_binary_layernorm(
         auto mean_x        = means[0];
         auto mean_x2       = means[1];
         auto variance      = mean_x2 - (mean_x * mean_x);
+        value_type eps_val = eps; // implicit conversion for eps
 
         r.inner([&](auto& y, auto x1, auto x2, auto... xs) {
             auto x = op(x1, x2);
             auto m = x - mean_x;
-            // m * rsqrt(mean(m ^ 2) + 1e-12)
-            y = compute(m * rsqrt(variance + value_type{1e-12}), xs...);
+
+            // m * rsqrt(mean(m ^ 2) + epsilon)
+            y = compute(m * rsqrt(variance + eps_val), xs...);
         })(output, input1, input2, inputs...);
     });
 }
 
 template <index_int Axis, class F, class Output, class Input, class... Inputs>
-__device__ void layernorm(F compute, Output output, Input input, Inputs... inputs)
+__device__ void layernorm(F compute, float eps, Output output, Input input, Inputs... inputs)
 {
     generic_binary_layernorm<Axis>(
-        compute, [](auto x, auto) { return x; }, output, input, input, inputs...);
+        compute, [](auto x, auto) { return x; }, eps, output, input, input, inputs...);
 }
 
 template <index_int Axis, class F, class Output, class Input1, class Input2, class... Inputs>
 __device__ void
-add_layernorm(F compute, Output output, Input1 input1, Input2 input2, Inputs... inputs)
+add_layernorm(F compute, float eps, Output output, Input1 input1, Input2 input2, Inputs... inputs)
 {
     generic_binary_layernorm<Axis>(
-        compute, [](auto x1, auto x2) { return x1 + x2; }, output, input1, input2, inputs...);
+        compute, [](auto x1, auto x2) { return x1 + x2; }, eps, output, input1, input2, inputs...);
 }
 
 } // namespace migraphx

src/targets/gpu/prefuse_ops.cpp

@@ -35,6 +35,12 @@ namespace {
 template <class Derived, std::size_t N>
 struct layernorm_base
 {
+    float epsilon = 1e-12f;
+    template <class Self, class F>
+    static auto reflect(Self& self, F f)
+    {
+        return pack(f(self.epsilon, "epsilon"));
+    }
     shape compute_shape(std::vector<shape> inputs, std::vector<module_ref> mods) const
     {
         std::size_t nargs = 1;
@@ -62,6 +68,7 @@ struct layernorm_base
 
 struct layernorm : layernorm_base<layernorm, 0>
 {
+
     std::string name() const { return "gpu::prelayernorm"; }
 };
 MIGRAPHX_REGISTER_OP(layernorm);
@@ -80,8 +87,9 @@ struct find_layernorm
     {
         auto ins   = r.result;
         auto x_ins = r.instructions["x"];
+        auto eps   = r.instructions["eps"]->eval().at<float>();
 
-        m.replace_instruction(ins, layernorm{}, x_ins);
+        m.replace_instruction(ins, layernorm{eps}, x_ins);
     }
 };
 
@@ -96,8 +104,9 @@ struct find_add_layernorm
     {
         auto ins     = r.result;
         auto add_ins = r.instructions["add"];
+        auto eps     = r.instructions["eps"]->eval().at<float>();
 
-        m.replace_instruction(ins, add_layernorm{}, add_ins->inputs());
+        m.replace_instruction(ins, add_layernorm{eps}, add_ins->inputs());
     }
 };
 } // namespace

test/verify/test_layernorm.cpp

@@ -29,14 +29,16 @@
 
 #include <migraphx/op/reduce_mean.hpp>
 
-migraphx::instruction_ref
-add_layernorm(migraphx::module& m, migraphx::instruction_ref x, std::vector<size_t> dims)
+migraphx::instruction_ref add_layernorm(migraphx::module& m,
+                                        migraphx::instruction_ref x,
+                                        std::vector<size_t> dims,
+                                        float eps = 1e-12f)
 {
     auto scale =
         m.add_parameter("scale", migraphx::shape{migraphx::shape::float_type, {dims.back()}});
     auto bias =
         m.add_parameter("bias", migraphx::shape{migraphx::shape::float_type, {dims.back()}});
-    auto epsilon  = m.add_literal(1e-12f);
+    auto epsilon  = m.add_literal(eps);
     auto exponent = m.add_literal(2.0f);
 
     auto mean = m.add_instruction(migraphx::op::reduce_mean({2}), x);
@@ -88,6 +90,19 @@ struct test_layernorm2 : verify_program<test_layernorm2>
     }
 };
 
+struct test_layernorm_eps : verify_program<test_layernorm_eps>
+{
+    migraphx::program create_program() const
+    {
+        migraphx::program p;
+        auto* mm                 = p.get_main_module();
+        std::vector<size_t> dims = {1, 2, 5};
+        auto x = mm->add_parameter("x", migraphx::shape{migraphx::shape::float_type, dims});
+        add_layernorm(*mm, x, dims, 1e-5f);
+        return p;
+    }
+};
+
 struct test_layernorm_triadd : verify_program<test_layernorm_triadd>
 {
     migraphx::program create_program() const